Adding upstream version 124.0.1.upstream/124.0.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

9 files changed, 11156 insertions, 0 deletions

diff --git a/servo/ports/geckolib/Cargo.toml b/servo/ports/geckolib/Cargo.toml
new file mode 100644
index 0000000000..ebf4178014
--- /dev/null
+++ b/servo/ports/geckolib/Cargo.toml
@@ -0,0 +1,33 @@
+[package]
+name = "geckoservo"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+
+[lib]
+name = "geckoservo"
+path = "lib.rs"
+
+[features]
+gecko_debug = ["style/gecko_debug", "nsstring/gecko_debug"]
+gecko_refcount_logging = ["style/gecko_refcount_logging", "servo_arc/gecko_refcount_logging"]
+
+[dependencies]
+atomic_refcell = "0.1"
+bincode = "1.0"
+cssparser = "0.33"
+cstr = "0.2"
+dom = { path = "../../../dom/base/rust" }
+gecko-profiler = { path = "../../../tools/profiler/rust-api" }
+libc = "0.2"
+log = {version = "0.4", features = ["release_max_level_info"]}
+malloc_size_of = {path = "../../components/malloc_size_of"}
+nsstring = {path = "../../../xpcom/rust/nsstring/"}
+num-traits = "0.2"
+selectors = {path = "../../components/selectors"}
+servo_arc = {path = "../../components/servo_arc"}
+smallvec = "1.0"
+style = {path = "../../components/style", features = ["gecko"]}
+style_traits = {path = "../../components/style_traits"}
+thin-vec = { version = "0.2.1", features = ["gecko-ffi"] }
+to_shmem = {path = "../../components/to_shmem"}
diff --git a/servo/ports/geckolib/cbindgen.toml b/servo/ports/geckolib/cbindgen.toml
new file mode 100644
index 0000000000..b703dc6c92
--- /dev/null
+++ b/servo/ports/geckolib/cbindgen.toml
@@ -0,0 +1,1076 @@
+header = """/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// See the comment in ServoBindings.h about the same.
+#pragma GCC diagnostic push
+#ifdef __clang__
+#  pragma GCC diagnostic ignored "-Wreturn-type-c-linkage"
+#endif
+// Work-around silly windows.h define.
+#pragma push_macro("STRICT")
+#undef STRICT
+#pragma push_macro("TRANSPARENT")
+#undef TRANSPARENT
+"""
+trailer = """
+#pragma pop_macro("STRICT")
+#pragma pop_macro("TRANSPARENT")
+#pragma GCC diagnostic pop
+#include "mozilla/ServoStyleConstsInlines.h"
+"""
+autogen_warning = """/* DO NOT MODIFY THIS MANUALLY! This file was generated using cbindgen.
+ * To generate this file:
+ *   1. Get the latest cbindgen using `cargo install --force cbindgen`
+ *      a. Alternatively, you can clone `https://github.com/eqrion/cbindgen` and use a tagged release
+ *   2. Run `rustup run nightly cbindgen toolkit/library/rust/ --lockfile Cargo.lock --crate style -o layout/style/ServoStyleConsts.h`
+ */
+"""
+include_guard = "mozilla_ServoStyleConsts_h"
+include_version = true
+braces = "SameLine"
+line_length = 80
+tab_width = 2
+language = "C++"
+namespaces = ["mozilla"]
+includes = ["mozilla/ServoStyleConstsForwards.h", "mozilla/ServoStyleSet.h"]
+
+[parse]
+parse_deps = true
+extra_bindings = ["style"]
+include = ["style", "app_units", "cssparser", "style_traits", "servo_arc"]
+
+[struct]
+associated_constants_in_body = true
+derive_eq = true
+derive_neq = true
+
+[defines]
+# These will actually never be defined, but is handy to avoid cbindgen
+# generating Servo-only types.
+"feature = servo" = "CBINDGEN_IS_SERVO"
+"feature = servo-layout-2013" = "CBINDGEN_IS_SERVO"
+"feature = servo-layout-2020" = "CBINDGEN_IS_SERVO"
+# These will always be defined.
+"feature = gecko" = "CBINDGEN_IS_GECKO"
+"feature = cbindgen" = "CBINDGEN_IS_GECKO"
+# These depend on the build.
+"target_pointer_width = 32" = "SERVO_32_BITS"
+"target_pointer_width = 64" = "HAVE_64BIT_BUILD"
+"unix" = "XP_UNIX"
+"windows" = "XP_WIN"
+
+[macro_expansion]
+bitflags = true
+
+[enum]
+derive_helper_methods = true
+derive_const_casts = true
+derive_tagged_enum_destructor = true
+derive_tagged_enum_copy_constructor = true
+derive_tagged_enum_copy_assignment = true
+private_default_tagged_enum_constructor = true
+cast_assert_name = "MOZ_DIAGNOSTIC_ASSERT"
+
+[export]
+prefix = "Style"
+exclude = [
+  "NS_LogCtor",
+  "NS_LogDtor",
+  "SelectorList",
+  "AuthorStyles",
+]
+include = [
+  "AnimationTimeline",
+  "AnimationIterationCount",
+  "AnimationDirection",
+  "AnimationFillMode",
+  "AnimationPlayState",
+  "AnimationComposition",
+  "Appearance",
+  "Au",
+  "BreakBetween",
+  "BreakWithin",
+  "BorderStyle",
+  "BoolInteger",
+  "OutlineStyle",
+  "CaptionSide",
+  "FontSizeAdjust",
+  "FontPalette",
+  "ComputedFontStretchRange",
+  "ComputedFontStyleDescriptor",
+  "ComputedFontWeightRange",
+  "ComputedTimingFunction",
+  "ComputedValueFlags",
+  "CursorKind",
+  "Display",
+  "DisplayOutside",
+  "DisplayInside",
+  "DisplayMode",
+  "Platform",
+  "GtkThemeFamily",
+  "PrefersColorScheme",
+  "PrefersContrast",
+  "DynamicRange",
+  "Scripting",
+  "FillRule",
+  "FontDisplay",
+  "FontFaceSourceListComponent",
+  "FontFaceSourceTechFlags",
+  "FontLanguageOverride",
+  "FontSynthesis",
+  "GenericFontFamily",
+  "FontFamily",
+  "FontFamilyNameSyntax",
+  "MozTheme",
+  "OverflowWrap",
+  "OffsetPath",
+  "OffsetPathFunction",
+  "OffsetPosition",
+  "OffsetRotate",
+  "RayFunction",
+  "UnicodeRange",
+  "UserSelect",
+  "Float",
+  "Clear",
+  "OverscrollBehavior",
+  "ScrollSnapAlign",
+  "ScrollSnapAxis",
+  "ScrollSnapStop",
+  "ScrollSnapStrictness",
+  "ScrollSnapType",
+  "ScrollTimelineName",
+  "ViewTimelineInset",
+  "OverflowAnchor",
+  "OverflowClipBox",
+  "Resize",
+  "Overflow",
+  "LengthPercentage",
+  "LetterSpacing",
+  "NonNegativeLengthPercentage",
+  "LengthPercentageOrAuto",
+  "LineHeight",
+  "NonNegativeLengthPercentageOrAuto",
+  "NonNegativeLengthPercentageOrNormal",
+  "LengthOrAuto",
+  "NonNegativeLengthOrAuto",
+  "TextDecorationSkipInk",
+  "TextDecorationLength",
+  "Time",
+  "Rect",
+  "IntersectionObserverRootMargin",
+  "Size",
+  "MaxSize",
+  "FlexBasis",
+  "Position",
+  "PositionOrAuto",
+  "BackgroundSize",
+  "BaselineSource",
+  "BorderImageSlice",
+  "BorderSpacing",
+  "BorderRadius",
+  "ColorScheme",
+  "NonNegativeLengthOrNumberRect",
+  "Perspective",
+  "ZIndex",
+  "TransformBox",
+  "TransformOrigin",
+  "LineBreak",
+  "LineClamp",
+  "WordBreak",
+  "Contain",
+  "ContainerType",
+  "ContainerName",
+  "ContentVisibility",
+  "ContainIntrinsicSize",
+  "Origin",
+  "RestyleHint",
+  "TouchAction",
+  "WillChange",
+  "TextDecorationLine",
+  "MasonryAutoFlow",
+  "MasonryPlacement",
+  "MasonryItemOrder",
+  "TextUnderlinePosition",
+  "TextTransform",
+  "TextJustify",
+  "TextOverflow",
+  "TextIndent",
+  "MozControlCharacterVisibility",
+  "RubyPosition",
+  "Owned",
+  "OwnedOrNull",
+  "Strong",
+  "ScrollbarColor",
+  "CaretColor",
+  "Color",
+  "ColorOrAuto",
+  "SystemColor",
+  "SystemColorScheme",
+  "SystemFont",
+  "GradientItem",
+  "VerticalAlign",
+  "BasicShape",
+  "InsetRect",
+  "ShapeRadius",
+  "ArcSlice",
+  "ForgottenArcSlicePtr",
+  "HeaderWithLength",
+  "MozContextProperties",
+  "Quotes",
+  "BoxShadow",
+  "SimpleShadow",
+  "Transform",
+  "Rotate",
+  "Scale",
+  "Translate",
+  "BorderImageWidth",
+  "ComputedUrl",
+  "ComputedImageUrl",
+  "UrlOrNone",
+  "Filter",
+  "Gradient",
+  "GridTemplateAreas",
+  "GridLine",
+  "TrackSize",
+  "TrackBreadth",
+  "ImplicitGridTracks",
+  "SVGPaint",
+  "SVGPaintKind",
+  "GridTemplateComponent",
+  "TextEmphasisStyle",
+  "TextEmphasisPosition",
+  "FontVariantAlternates",
+  "PaintOrder",
+  "SVGPaintOrder",
+  "ClipRectOrAuto",
+  "CounterReset",
+  "CounterSet",
+  "CounterIncrement",
+  "WritingMode",
+  "Content",
+  "ContentItem",
+  "AlignSelf",
+  "JustifySelf",
+  "AlignItems",
+  "ComputedJustifyItems",
+  "AlignContent",
+  "JustifyContent",
+  "AlignTracks",
+  "JustifyTracks",
+  "TransformStyle",
+  "Image",
+  "ClipPath",
+  "ShapeOutside",
+  "GridAutoFlow",
+  "Cursor",
+  "SVGStrokeDashArray",
+  "SVGLength",
+  "SVGOpacity",
+  "SVGWidth",
+  "TextAlign",
+  "TextAlignLast",
+  "FontSizeKeyword",
+  "AspectRatio",
+  "DefaultFontSizes",
+  "RuleChangeKind",
+  "PageName",
+  "PageOrientation",
+  "PageSize",
+  "DProperty",
+  "ImageRendering",
+  "PrintColorAdjust",
+  "ForcedColorAdjust",
+  "ScrollbarGutter",
+  "ScrollDirection",
+  "HyphenateCharacter",
+  "ComputedLinearStop",
+  "PiecewiseLinearFunction",
+  "BeforeFlag",
+  "XTextScale",
+  "Zoom",
+  "TransitionProperty",
+]
+item_types = ["enums", "structs", "unions", "typedefs", "functions", "constants"]
+renaming_overrides_prefixing = true
+
+# Prevent some renaming for Gecko types that cbindgen doesn't otherwise understand.
+[export.rename]
+"nscolor" = "nscolor"
+"nsAtom" = "nsAtom"
+"nsIURI" = "nsIURI"
+"imgRequestProxy" = "imgRequestProxy"
+"nsCompatibility" = "nsCompatibility"
+"nsSimpleContentList" = "nsSimpleContentList"
+"nsACString" = "nsACString"
+"nsAString" = "nsAString"
+"nsCString" = "nsCString"
+"nsString" = "nsString"
+"CopyableTArray" = "CopyableTArray"
+"nsTArray" = "nsTArray"
+"nsPresContext" = "nsPresContext"
+"ComputedTiming" = "ComputedTiming"
+"CountedUnknownProperty" = "CountedUnknownProperty"
+"RefPtr" = "RefPtr"
+"nsCSSPropertyID" = "nsCSSPropertyID"
+"nsCSSPropertyIDSet" = "nsCSSPropertyIDSet"
+"AnimatedPropertyID" = "AnimatedPropertyID"
+"nsCSSValueSharedList" = "nsCSSValueSharedList"
+"AnimationPropertySegment" = "AnimationPropertySegment"
+"RawServoAnimationValueTable" = "RawServoAnimationValueTable"
+"nsCSSUnit" = "nsCSSUnit"
+"InheritTarget" = "InheritTarget"
+"PseudoStyleType" = "PseudoStyleType"
+"DeclarationBlockMutationClosure" = "DeclarationBlockMutationClosure"
+"AtomArray" = "AtomArray"
+"UpdateAnimationsTasks" = "UpdateAnimationsTasks"
+"StyleRuleInclusion" = "StyleRuleInclusion"
+"nsFontFaceRuleContainer" = "nsFontFaceRuleContainer"
+"MediumFeaturesChangedResult" = "MediumFeaturesChangedResult"
+"FontSizePrefs" = "FontSizePrefs"
+"nsCSSFontDesc" = "nsCSSFontDesc"
+"nsresult" = "nsresult"
+"gfxFontFeature" = "gfxFontFeature"
+"gfxFontFeatureValueSet" = "gfxFontFeatureValueSet"
+"GeckoFontMetrics" = "GeckoFontMetrics"
+"SeenPtrs" = "SeenPtrs"
+"gfxFontVariation" = "gfxFontVariation"
+"URLExtraData" = "URLExtraData"
+"Keyframe" = "Keyframe"
+"nsChangeHint" = "nsChangeHint"
+"ServoElementSnapshotTable" = "ServoElementSnapshotTable"
+"Keyframe" = "Keyframe"
+"ComputedKeyframeValues" = "ComputedKeyframeValues"
+"OriginFlags" = "OriginFlags"
+"ServoTraversalFlags" = "ServoTraversalFlags"
+"ServoStyleSetSizes" = "ServoStyleSetSizes"
+"BeforeFlag" = "StyleEasingBeforeFlag"
+"FontPaletteValueSet" = "gfx::FontPaletteValueSet"
+"PaletteValues" = "gfx::FontPaletteValueSet::PaletteValues"
+"ThinVec" = "nsTArray"
+"RawPthread" = "pthread_t"
+"RawHandle" = "void*"
+
+[export.body]
+"CSSPixelLength" = """
+  static StyleCSSPixelLength FromPixels(CSSCoord aCoord) { return {aCoord}; }
+  static StyleCSSPixelLength Zero() { return FromPixels(0.0f); }
+
+  inline nscoord ToAppUnits() const;
+  inline bool IsZero() const;
+  CSSCoord ToCSSPixels() const { return _0; }
+  inline void ScaleBy(float);
+  inline StyleCSSPixelLength ScaledBy(float) const;
+"""
+
+"CalcLengthPercentage" = """
+  inline CSSCoord ResolveToCSSPixels(CSSCoord aBasis) const;
+
+  using CoordRounder = nscoord(*)(float);
+  nscoord Resolve(nscoord aBasis, CoordRounder) const;
+"""
+
+"GenericCalcNode" = """
+  void ScaleLengthsBy(float);
+"""
+
+"LengthPercentageUnion" = """
+  using Self = StyleLengthPercentageUnion;
+
+  // TODO(emilio): cbindgen should be able to generate these in the body of the
+  // union, but it seems it's only implemented for structs, not unions.
+  static const uint8_t TAG_CALC = StyleLengthPercentageUnion_TAG_CALC;
+  static const uint8_t TAG_LENGTH = StyleLengthPercentageUnion_TAG_LENGTH;
+  static const uint8_t TAG_PERCENTAGE = StyleLengthPercentageUnion_TAG_PERCENTAGE;
+  static const uint8_t TAG_MASK = StyleLengthPercentageUnion_TAG_MASK;
+
+ private:
+  uint8_t Tag() const {
+    return tag.tag & TAG_MASK;
+  }
+
+ public:
+  // We need to do all this manually because cbingen can't reason about unions.
+  inline StyleLengthPercentageUnion();
+  inline StyleLengthPercentageUnion(const Self&);
+  inline ~StyleLengthPercentageUnion();
+  inline Self& operator=(const Self&);
+
+  inline bool operator==(const Self& aOther) const;
+  inline bool operator!=(const Self& aOther) const;
+
+  inline bool IsLength() const;
+  inline bool IsPercentage() const;
+  inline bool IsCalc() const;
+
+  inline const StyleLength& AsLength() const;
+  inline StyleLength& AsLength();
+
+  inline const StylePercentage& AsPercentage() const;
+  inline StylePercentage& AsPercentage();
+
+  inline const StyleCalcLengthPercentage& AsCalc() const;
+  inline StyleCalcLengthPercentage& AsCalc();
+
+  static inline Self Zero();
+  static inline Self FromAppUnits(nscoord);
+  static inline Self FromPixels(CSSCoord);
+  static inline Self FromPercentage(float);
+
+  inline void ScaleLengthsBy(float);
+  inline bool HasPercent() const;
+  inline bool ConvertsToLength() const;
+  inline nscoord ToLength() const;
+  inline CSSCoord ToLengthInCSSPixels() const;
+  inline bool ConvertsToPercentage() const;
+  inline bool HasLengthAndPercentage() const;
+  inline float ToPercentage() const;
+  inline bool IsDefinitelyZero() const;
+  inline CSSCoord ResolveToCSSPixels(CSSCoord aPercentageBasisInCSSPixels) const;
+  template<typename T> inline CSSCoord ResolveToCSSPixelsWith(T aPercentageGetter) const;
+  template<typename T, typename U>
+  inline nscoord Resolve(T aPercentageGetter, U aRoundingFunction) const;
+  template<typename T>
+  inline nscoord Resolve(nscoord aPercentageBasis, T aRoundingFunction) const;
+  template<typename T> inline nscoord Resolve(T aPercentageGetter) const;
+  inline nscoord Resolve(nscoord aPercentageBasis) const;
+"""
+
+"GenericLengthPercentageOrAuto" = """
+  inline bool ConvertsToLength() const;
+  inline nscoord ToLength() const;
+  inline bool ConvertsToPercentage() const;
+  inline float ToPercentage() const;
+  inline bool HasPercent() const;
+  inline bool HasLengthAndPercentage() const;
+
+  // Just some convenient aliases for LengthOrAuto, to avoid confusing naming.
+  inline bool IsLength() const;
+  inline const StyleLength& AsLength() const;
+
+  static inline StyleGenericLengthPercentageOrAuto Zero();
+"""
+
+"GenericSize" = """
+  inline bool ConvertsToLength() const;
+  inline nscoord ToLength() const;
+  inline bool ConvertsToPercentage() const;
+  inline float ToPercentage() const;
+  inline bool HasPercent() const;
+  inline bool HasLengthAndPercentage() const;
+  inline bool BehavesLikeInitialValueOnBlockAxis() const;
+"""
+
+"GenericFlexBasis" = """
+  inline bool IsAuto() const;
+"""
+
+"GenericMaxSize" = """
+  inline bool ConvertsToLength() const;
+  inline nscoord ToLength() const;
+  inline bool ConvertsToPercentage() const;
+  inline float ToPercentage() const;
+  inline bool HasPercent() const;
+  inline bool HasLengthAndPercentage() const;
+  inline bool BehavesLikeInitialValueOnBlockAxis() const;
+"""
+
+"GenericPosition" = """
+  inline bool HasPercent() const;
+  inline bool DependsOnPositioningAreaSize() const;
+  static inline StyleGenericPosition FromPercentage(float);
+"""
+
+"GenericBackgroundSize" = """
+  bool IsInitialValue() const;
+"""
+
+"Rect" = """
+  template<typename Predicate> inline bool All(Predicate) const;
+  template<typename Predicate> inline bool Any(Predicate) const;
+
+  // Defined in WritingModes.h
+  inline const T& Get(mozilla::Side) const;
+  inline const T& Get(WritingMode, LogicalSide) const;
+  inline const T& GetIStart(WritingMode) const;
+  inline const T& GetBStart(WritingMode) const;
+  inline const T& Start(LogicalAxis, WritingMode) const;
+  inline const T& GetIEnd(WritingMode) const;
+  inline const T& GetBEnd(WritingMode) const;
+  inline const T& End(LogicalAxis, WritingMode) const;
+
+  inline T& Get(mozilla::Side);
+  inline T& Get(WritingMode, LogicalSide);
+  inline T& GetIStart(WritingMode);
+  inline T& GetBStart(WritingMode);
+  inline T& GetIEnd(WritingMode);
+  inline T& GetBEnd(WritingMode);
+
+  static StyleRect WithAllSides(const T& aSide) {
+    return {aSide, aSide, aSide, aSide};
+  }
+"""
+
+"GenericBorderRadius" = """
+  inline const StyleLengthPercentage& Get(HalfCorner) const;
+"""
+
+"RestyleHint" = """
+  static inline StyleRestyleHint RestyleSubtree();
+  static inline StyleRestyleHint RecascadeSubtree();
+  static inline StyleRestyleHint ForAnimations();
+  // Returns true if this change hint is guaranteed to at least recascade all
+  // elements in the subtree of the element it is applied to.
+  inline bool DefinitelyRecascadesAllSubtree() const;
+"""
+
+"TextTransform" = """
+  static inline StyleTextTransform None();
+  inline bool IsNone() const;
+"""
+
+"TextUnderlinePosition" = """
+  inline bool IsAuto() const;
+  inline bool IsFromFont() const;
+  inline bool IsUnder() const;
+  inline bool IsLeft() const;
+  inline bool IsRight() const;
+"""
+
+# TODO(emilio): Add hooks to cbindgen to be able to generate [[nodiscard]]
+# on the functions.
+"Owned" = """
+  UniquePtr<GeckoType> Consume() {
+    UniquePtr<GeckoType> ret(ptr);
+    ptr = nullptr;
+    return ret;
+  }
+"""
+
+"OwnedOrNull" = """
+  UniquePtr<GeckoType> Consume() {
+    UniquePtr<GeckoType> ret(ptr);
+    ptr = nullptr;
+    return ret;
+  }
+"""
+
+"Strong" = """
+  already_AddRefed<GeckoType> Consume() {
+    already_AddRefed<GeckoType> ret(const_cast<GeckoType*>(ptr));
+    ptr = nullptr;
+    return ret;
+  }
+"""
+
+"GenericColor" = """
+  static inline StyleGenericColor FromColor(nscolor);
+
+  static inline StyleGenericColor Transparent();
+  static inline StyleGenericColor Black();
+  static inline StyleGenericColor White();
+
+  bool MaybeTransparent() const;
+
+  /**
+   * Compute the final color, taking into account the foreground color.
+   **/
+  StyleAbsoluteColor ResolveColor(const StyleAbsoluteColor&) const;
+
+  /**
+   * Compute the final color, taking into account the foreground color from the
+   * frame's ComputedStyle.
+   */
+  nscolor CalcColor(const nsIFrame*) const;
+  /**
+   * Compute the final color, taking into account the foreground color from the
+   * style.
+   */
+  nscolor CalcColor(const ComputedStyle&) const;
+  /**
+   * Compute the final color, making the argument the foreground color.
+   */
+  nscolor CalcColor(nscolor) const;
+  nscolor CalcColor(const StyleAbsoluteColor&) const;
+"""
+
+"AbsoluteColor" = """
+  /**
+   * Create a new AbsoluteColor in the sRGB color space in legacy color syntax.
+   */
+  static inline StyleAbsoluteColor SrgbLegacy(float red, float green, float blue, float alpha);
+
+  static inline StyleAbsoluteColor FromColor(nscolor);
+
+  /**
+   * Convert this color into the given color space.
+   */
+  StyleAbsoluteColor ToColorSpace(StyleColorSpace aColorSpace) const;
+
+  /**
+   * Convert this color to an nscolor. The color will be converted to sRGB first
+   * if required.
+   */
+  nscolor ToColor() const;
+"""
+
+"OwnedSlice" = """
+  constexpr StyleOwnedSlice() :
+    ptr((T*)alignof(T)),
+    len(0) {}
+
+  inline void Clear();
+  inline void CopyFrom(const StyleOwnedSlice&);
+  inline void SwapElements(StyleOwnedSlice&);
+
+  StyleOwnedSlice& operator=(const StyleOwnedSlice&);
+  StyleOwnedSlice& operator=(StyleOwnedSlice&&);
+
+  inline StyleOwnedSlice(const StyleOwnedSlice&);
+  inline StyleOwnedSlice(StyleOwnedSlice&&);
+  inline explicit StyleOwnedSlice(Vector<T>&&);
+
+  inline ~StyleOwnedSlice();
+
+  Span<const T> AsSpan() const {
+    return {ptr, len};
+  }
+
+  size_t Length() const {
+    return len;
+  }
+
+  bool IsEmpty() const { return Length() == 0; }
+
+  bool operator==(const StyleOwnedSlice& other) const {
+    return AsSpan() == other.AsSpan();
+  }
+
+  bool operator!=(const StyleOwnedSlice& other) const {
+    return !(*this == other);
+  }
+"""
+
+"ArcInner" = """
+  // Increase the reference count.
+  inline void IncrementRef();
+  // Release the reference count, and return whether the result must be freed or not.
+  [[nodiscard]] inline bool DecrementRef();
+"""
+
+"HeaderSlice" = """
+  StyleHeaderSlice() = delete;
+  StyleHeaderSlice(const StyleHeaderSlice&) = delete;
+
+  inline ~StyleHeaderSlice();
+  inline bool operator==(const StyleHeaderSlice& other) const;
+  inline bool operator!=(const StyleHeaderSlice& other) const;
+
+  inline Span<const T> AsSpan() const;
+  inline size_t Length() const { return len; }
+  inline bool IsEmpty() const { return len == 0; }
+"""
+
+"ArcSlice" = """
+  inline StyleArcSlice();
+  inline explicit StyleArcSlice(const StyleForgottenArcSlicePtr<T>& aPtr);
+  inline Span<const T> AsSpan() const;
+  inline size_t Length() const;
+  inline bool IsEmpty() const;
+"""
+
+"Arc" = """
+  StyleArc() = delete;
+  inline StyleArc(const StyleArc& Other);
+ private:
+  inline void Release();
+ public:
+  explicit StyleArc(decltype(p) aP) : p(aP) {
+    MOZ_DIAGNOSTIC_ASSERT(p, "Arc shouldn't be null");
+  }
+  inline ~StyleArc();
+
+  inline StyleArc& operator=(const StyleArc&);
+  inline StyleArc& operator=(StyleArc&&);
+
+  const T* operator->() const {
+    MOZ_DIAGNOSTIC_ASSERT(p, "Arc shouldn't be null");
+    return &p->data;
+  }
+  const T& operator*() const {
+    MOZ_DIAGNOSTIC_ASSERT(p, "Arc shouldn't be null");
+    return p->data;
+  }
+  bool operator==(const StyleArc& other) const {
+    return p == other.p || *(*this) == *other;
+  }
+  bool operator!=(const StyleArc& other) const {
+    return !(*this == other);
+  }
+"""
+
+"CustomIdent" = """
+  inline nsAtom* AsAtom() const;
+"""
+
+"Atom" = """
+  StyleAtom(size_t) = delete;
+  StyleAtom() = delete;
+
+  inline bool IsStatic() const;
+  inline nsAtom* AsAtom() const;
+
+ private:
+  inline void AddRef();
+  inline void Release();
+
+ public:
+  inline explicit StyleAtom(already_AddRefed<nsAtom>);
+  inline explicit StyleAtom(nsStaticAtom*);
+  inline StyleAtom(const StyleAtom& aOther);
+  inline StyleAtom& operator=(const StyleAtom&);
+  inline ~StyleAtom();
+"""
+
+"OwnedStr" = """
+  inline nsDependentCSubstring AsString() const;
+"""
+
+"GenericTransformOrigin" = """
+  inline bool HasPercent() const;
+"""
+
+"GenericTransform" = """
+  inline Span<const T> Operations() const;
+  inline bool IsNone() const;
+  bool HasPercent() const;
+"""
+
+"Angle" = """
+  inline static StyleAngle Zero();
+  inline float ToDegrees() const;
+  inline double ToRadians() const;
+  StyleAngle operator+(const StyleAngle& aAngle) const {
+    return StyleAngle{_0 + aAngle._0};
+  }
+  StyleAngle operator-(const StyleAngle& aAngle) const {
+    return StyleAngle{_0 - aAngle._0};
+  }
+"""
+
+"CoordPair" = """
+  explicit StyleCoordPair(const gfx::Point& aPoint): x(aPoint.x), y(aPoint.y) {}
+  gfx::Point ConvertsToGfxPoint() const { return gfx::Point(x, y); }
+"""
+
+"TextOverflow" = """
+  StyleTextOverflow()
+    : first(StyleTextOverflowSide::Clip()),
+      second(StyleTextOverflowSide::Clip()),
+      sides_are_logical(true) {}
+"""
+
+"GenericTextIndent" = """
+  StyleGenericTextIndent()
+    : length(StyleLengthPercentage::Zero()),
+      hanging(false),
+      each_line(false) {}
+"""
+
+"UrlExtraData" = """
+  StyleUrlExtraData() = delete;
+
+  // Could be implemented if wanted.
+  StyleUrlExtraData(const StyleUrlExtraData&) = delete;
+  StyleUrlExtraData& operator=(const StyleUrlExtraData&) = delete;
+
+  inline bool IsShared() const;
+
+  inline ~StyleUrlExtraData();
+  inline const URLExtraData& get() const;
+"""
+
+"CssUrlData" = """
+  // Implemented in nsStyleStruct.cpp
+  bool operator==(const StyleCssUrlData& other) const;
+  bool operator!=(const StyleCssUrlData& other) const {
+    return !(*this == other);
+  }
+"""
+
+"LoadData" = """
+  ~StyleLoadData();
+"""
+
+"CssUrl" = """
+  inline nsDependentCSubstring SpecifiedSerialization() const;
+  inline const URLExtraData& ExtraData() const;
+  inline StyleLoadData& LoadData() const;
+  inline nsIURI* GetURI() const;
+"""
+
+"ComputedUrl" = """
+  // Forwarded from CssUrl.
+  inline nsDependentCSubstring SpecifiedSerialization() const;
+  inline const URLExtraData& ExtraData() const;
+  inline nsIURI* GetURI() const;
+  inline StyleLoadData& LoadData() const;
+
+  inline bool IsLocalRef() const;
+  inline bool HasRef() const;
+  inline StyleCorsMode CorsMode() const;
+  already_AddRefed<nsIURI> ResolveLocalRef(nsIURI* aBase) const;
+  already_AddRefed<nsIURI> ResolveLocalRef(const nsIContent* aContent) const;
+
+  // Only relevant for images.
+  inline bool IsImageResolved() const;
+  inline imgRequestProxy* GetImage() const;
+  void ResolveImage(dom::Document&, const StyleComputedUrl* aOldImage);
+"""
+
+"GenericGradient" = """
+  inline bool Repeating() const;
+  bool IsOpaque() const;
+
+  // Return the color interpolation method of the gradient.
+  inline const StyleColorInterpolationMethod& ColorInterpolationMethod() const;
+"""
+
+"GenericGridLine" = """
+  // Returns the `auto` value.
+  inline StyleGenericGridLine();
+  inline bool IsAuto() const;
+  // The line name, or nsGkAtoms::_empty if not present.
+  inline nsAtom* LineName() const;
+"""
+
+"GenericTrackBreadth" = """
+  inline bool HasPercent() const;
+"""
+
+"GenericTrackSize" = """
+  // Implemented in nsGridContainerFrame.cpp
+  inline const StyleGenericTrackBreadth<L>& GetMin() const;
+  inline const StyleGenericTrackBreadth<L>& GetMax() const;
+"""
+
+"GenericGridTemplateComponent" = """
+  inline Maybe<size_t> RepeatAutoIndex() const;
+  inline const StyleGenericTrackRepeat<L, I>* GetRepeatAutoValue() const;
+  inline bool HasRepeatAuto() const;
+  inline Span<const StyleOwnedSlice<StyleCustomIdent>> LineNameLists(bool aIsSubgrid) const;
+  inline Span<const StyleGenericTrackListValue<L, I>> TrackListValues() const;
+"""
+
+"GenericClipRect" = """
+  // Get the layout rect, replacing auto right / bottom values for aAutoSize.
+  inline nsRect ToLayoutRect(nscoord aAutoSize = NS_MAXSIZE) const;
+"""
+
+"TimingFunction" = """
+ public:
+  bool IsLinearKeyword() const { return IsKeyword() && AsKeyword() == StyleTimingKeyword::Linear; }
+  static StyleTimingFunction LinearKeyword() { return Keyword(StyleTimingKeyword::Linear); }
+
+  inline double At(double, bool aBeforeFlag) const;
+  inline void AppendToString(nsACString&) const;
+
+  inline static double GetPortion(const Maybe<StyleTimingFunction>&, double, bool aBeforeFlag);
+"""
+
+"GenericImage" = """
+ public:
+  // Returns the intrinsic resolution of the image.
+  //
+  // The resolution is in dppx, and should be used to impact the intrinsic
+  // size of the image.
+  ImageResolution GetResolution(const ComputedStyle&) const;
+
+  // If this is an image-set(), the final image we've selected, otherwise it
+  // returns *this.
+  const StyleGenericImage& FinalImage() const;
+
+  // Whether this image may have an image request associated with it.
+  bool IsImageRequestType() const;
+
+  // Gets the image request URL.
+  const StyleComputedImageUrl* GetImageRequestURLValue() const;
+
+  // Gets the image data of this image if it has any image request.
+  imgRequestProxy* GetImageRequest() const;
+
+  // Returns true if this image is fully loaded, and its size is calculated.
+  // Always returns true if there's no image request involved and this image
+  // is not `none`.
+  bool IsComplete() const;
+
+  // Returns true if this image has an available size and hasn't errored.
+  // Always returns true if there's no image request involved and this image
+  // is not `none`.
+  bool IsSizeAvailable() const;
+
+  // Returns true if the item is definitely opaque --- i.e., paints every
+  // pixel within its bounds opaquely, and the bounds contains at least a pixel.
+  bool IsOpaque() const;
+
+  // Resolves the underlying image request if any.
+  void ResolveImage(dom::Document&, const StyleGenericImage* aOld);
+
+  // Returns whether this image has been resolved.
+  bool IsResolved() const;
+"""
+
+"Ratio" = """
+  inline AspectRatio ToLayoutRatio(UseBoxSizing aUseBoxSizing) const;
+"""
+
+"GenericAspectRatio" = """
+  bool HasRatio() const { return ratio.IsRatio(); }
+  bool HasFiniteRatio() const { return static_cast<bool>(ToLayoutRatio()); }
+  bool BehavesAsAuto() const { return auto_ || !HasFiniteRatio(); }
+  inline AspectRatio ToLayoutRatio() const;
+
+  static StyleGenericAspectRatio Auto() {
+    return {true, StylePreferredRatio<N>::None()};
+  }
+"""
+
+"FontFamilyList" = """
+  static StyleFontFamilyList WithOneUnquotedFamily(const nsACString&);
+  // Constructs a font family list with a list of names.
+  static StyleFontFamilyList WithNames(nsTArray<StyleSingleFontFamily>&&);
+"""
+
+"SingleFontFamily" = """
+  static StyleSingleFontFamily Parse(const nsACString& aName);
+  void AppendToString(nsACString& aFamily, bool aIncludeQuotes = true) const;
+  bool IsNamedFamily(const nsAString&) const;
+"""
+
+"TimelineOrKeyframesName" = """
+ public:
+  inline nsAtom* AsAtom() const;
+"""
+
+"FontWeight" = """
+ SERVO_FIXED_POINT_HELPERS(StyleFontWeight, uint16_t, StyleFONT_WEIGHT_FRACTION_BITS);
+ bool IsNormal() const { return *this == NORMAL; }
+
+ inline bool IsBold() const;
+"""
+
+"FontStyle" = """
+ SERVO_FIXED_POINT_HELPERS(StyleFontStyle, int16_t, StyleFONT_STYLE_FRACTION_BITS);
+ bool IsNormal() const { return *this == NORMAL; }
+ inline bool IsItalic() const;
+ inline bool IsOblique() const;
+ inline float ObliqueAngle() const;  // Only for use when IsOblique() is true
+ inline float SlantAngle() const;  // Returns angle for any font-style, including
+                                   // normal/italic as well as explicit oblique
+"""
+
+"FontStretch" = """
+ SERVO_FIXED_POINT_HELPERS(StyleFontStretch, uint16_t, StyleFONT_STRETCH_FRACTION_BITS);
+ bool IsNormal() const { return *this == NORMAL; }
+"""
+
+"Zoom" = """
+ SERVO_FIXED_POINT_HELPERS(StyleZoom, uint16_t, StyleZOOM_FRACTION_BITS);
+ inline float Zoom(float) const;
+ inline float Unzoom(float) const;
+ inline nscoord ZoomCoord(nscoord) const;
+ inline nscoord UnzoomCoord(nscoord) const;
+ inline nsSize Zoom(const nsSize&) const;
+ inline nsSize Unzoom(const nsSize&) const;
+ inline nsPoint Zoom(const nsPoint&) const;
+ inline nsPoint Unzoom(const nsPoint&) const;
+ inline nsRect Zoom(const nsRect&) const;
+ inline nsRect Unzoom(const nsRect&) const;
+"""
+
+"AnimationName" = """
+ public:
+  StyleAnimationName() : _0(nsGkAtoms::_empty) {}
+"""
+
+"GenericViewTimelineInset" = """
+ public:
+  inline StyleGenericViewTimelineInset();
+"""
+
+"Time" = """
+ float ToSeconds() const { return seconds; }
+ float ToMilliseconds() const { return seconds * 1000.0f; }
+"""
+
+"FontFaceSourceTechFlags" = """
+  inline static StyleFontFaceSourceTechFlags Empty() {
+    return StyleFontFaceSourceTechFlags{0};
+  }
+"""
+
+"FontPalette" = """
+  inline static StyleFontPalette Normal() {
+    return StyleFontPalette{StyleAtom(nsGkAtoms::normal->ToAddRefed())};
+  }
+"""
+
+"GenericOffsetPath" = """
+  // Return true if the <offset-path> is ray().
+  bool IsRay() const {
+    return IsOffsetPath() && AsOffsetPath().path->IsRay();
+  }
+
+  const StyleRayFunction& AsRay() const {
+    return AsOffsetPath().path->AsRay();
+  }
+
+  // Return true if the <offset-path> is url().
+  bool IsUrl() const {
+    return IsOffsetPath() && AsOffsetPath().path->IsUrl();
+  }
+
+  const StyleComputedUrl& AsUrl() const {
+    return AsOffsetPath().path->AsUrl();
+  }
+
+  // Return true if the <basic-shape> is path().
+  bool IsPath() const {
+    return IsOffsetPath() && AsOffsetPath().path->IsShape() &&
+           AsOffsetPath().path->AsShape().IsPath();
+  }
+
+  const StyleSVGPathData& AsSVGPathData() const {
+    return AsOffsetPath().path->AsShape().AsPath().path;
+  }
+
+  // Return true if this is "<basic-shape> || <coord-box>".
+  bool IsBasicShapeOrCoordBox() const {
+    return IsCoordBox() || (IsOffsetPath() && AsOffsetPath().path->IsShape());
+  }
+"""
+
+"GenericContainIntrinsicSize" = """
+  bool HasAuto() const { return IsAutoLength() || IsAutoNone(); }
+"""
+
+"Display" = """
+  inline StyleDisplayOutside Outside() const;
+  inline StyleDisplayInside Inside() const;
+  inline bool IsListItem() const;
+  inline bool IsInlineFlow() const;
+  inline bool IsInlineInside() const;
+  inline bool IsInlineOutside() const;
+  inline bool IsBlockOutside() const;
+  inline bool IsRuby() const;
+  inline bool IsInternalRuby() const;
+  inline bool IsInternalTable() const;
+  inline bool IsInternalTableExceptCell() const;
+"""
+
+"TransitionProperty" = """
+  bool IsAll() const {
+    return IsNonCustom() &&
+           nsCSSPropertyID(AsNonCustom()._0) == eCSSProperty_all;
+  }
+"""
diff --git a/servo/ports/geckolib/error_reporter.rs b/servo/ports/geckolib/error_reporter.rs
new file mode 100644
index 0000000000..78facf3371
--- /dev/null
+++ b/servo/ports/geckolib/error_reporter.rs
@@ -0,0 +1,514 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+//! Wrapper around Gecko's CSS error reporting mechanism.
+
+#![allow(unsafe_code)]
+
+use cssparser::{serialize_identifier, CowRcStr, ToCss};
+use cssparser::{BasicParseErrorKind, ParseError, ParseErrorKind, SourceLocation, Token};
+use selectors::parser::SelectorParseErrorKind;
+use selectors::SelectorList;
+use std::ffi::CStr;
+use std::ptr;
+use style::error_reporting::{ContextualParseError, ParseErrorReporter};
+use style::gecko_bindings::bindings;
+use style::gecko_bindings::structs::URLExtraData as RawUrlExtraData;
+use style::gecko_bindings::structs::{nsIURI, Loader, StyleSheet as DomStyleSheet};
+use style::selector_parser::SelectorImpl;
+use style::stylesheets::UrlExtraData;
+use style_traits::{PropertySyntaxParseError, StyleParseErrorKind, ValueParseErrorKind};
+
+pub type ErrorKind<'i> = ParseErrorKind<'i, StyleParseErrorKind<'i>>;
+
+/// An error reporter with all the data we need to report errors.
+pub struct ErrorReporter {
+    window_id: u64,
+    uri: *mut nsIURI,
+}
+
+impl ErrorReporter {
+    /// Create a new instance of the Gecko error reporter, if error reporting is
+    /// enabled.
+    pub fn new(
+        sheet: *mut DomStyleSheet,
+        loader: *mut Loader,
+        extra_data: *mut RawUrlExtraData,
+    ) -> Option<Self> {
+        let mut window_id = 0;
+
+        let enabled =
+            unsafe { bindings::Gecko_ErrorReportingEnabled(sheet, loader, &mut window_id) };
+
+        if !enabled {
+            return None;
+        }
+
+        let uri = unsafe {
+            extra_data
+                .as_ref()
+                .map(|d| d.mBaseURI.raw())
+                .unwrap_or(ptr::null_mut())
+        };
+
+        Some(ErrorReporter { window_id, uri })
+    }
+}
+
+enum ErrorString<'a> {
+    Snippet(CowRcStr<'a>),
+    Ident(CowRcStr<'a>),
+    UnexpectedToken(Token<'a>),
+}
+
+impl<'a> ErrorString<'a> {
+    fn into_str(self) -> CowRcStr<'a> {
+        match self {
+            ErrorString::Snippet(s) => s,
+            ErrorString::UnexpectedToken(t) => t.to_css_string().into(),
+            ErrorString::Ident(i) => {
+                let mut s = String::new();
+                serialize_identifier(&i, &mut s).unwrap();
+                s.into()
+            },
+        }
+    }
+}
+
+#[derive(Debug)]
+enum Action {
+    Nothing,
+    Skip,
+    Drop,
+}
+
+trait ErrorHelpers<'a> {
+    fn error_data(self) -> (CowRcStr<'a>, ErrorKind<'a>);
+    fn error_params(self) -> ErrorParams<'a>;
+    fn selectors(&self) -> &'a [SelectorList<SelectorImpl>];
+    fn to_gecko_message(&self) -> (Option<&'static CStr>, &'static CStr, Action);
+}
+
+fn extract_error_param<'a>(err: ErrorKind<'a>) -> Option<ErrorString<'a>> {
+    Some(match err {
+        ParseErrorKind::Basic(BasicParseErrorKind::UnexpectedToken(t)) => {
+            ErrorString::UnexpectedToken(t)
+        },
+
+        ParseErrorKind::Basic(BasicParseErrorKind::AtRuleInvalid(i)) => {
+            let mut s = String::from("@");
+            serialize_identifier(&i, &mut s).unwrap();
+            ErrorString::Snippet(s.into())
+        },
+
+        ParseErrorKind::Custom(StyleParseErrorKind::OtherInvalidValue(property)) => {
+            ErrorString::Snippet(property)
+        },
+
+        ParseErrorKind::Custom(StyleParseErrorKind::SelectorError(
+            SelectorParseErrorKind::UnexpectedIdent(ident),
+        )) => ErrorString::Ident(ident),
+
+        ParseErrorKind::Custom(StyleParseErrorKind::UnknownProperty(property)) => {
+            ErrorString::Ident(property)
+        },
+
+        ParseErrorKind::Custom(StyleParseErrorKind::UnexpectedTokenWithinNamespace(token)) => {
+            ErrorString::UnexpectedToken(token)
+        },
+
+        _ => return None,
+    })
+}
+
+struct ErrorParams<'a> {
+    prefix_param: Option<ErrorString<'a>>,
+    main_param: Option<ErrorString<'a>>,
+}
+
+/// If an error parameter is present in the given error, return it. Additionally return
+/// a second parameter if it exists, for use in the prefix for the eventual error message.
+fn extract_error_params<'a>(err: ErrorKind<'a>) -> Option<ErrorParams<'a>> {
+    let (main, prefix) = match err {
+        ParseErrorKind::Custom(StyleParseErrorKind::InvalidColor(property, token)) |
+        ParseErrorKind::Custom(StyleParseErrorKind::InvalidFilter(property, token)) => (
+            Some(ErrorString::Snippet(property.into())),
+            Some(ErrorString::UnexpectedToken(token)),
+        ),
+
+        ParseErrorKind::Custom(StyleParseErrorKind::MediaQueryExpectedFeatureName(ident)) => {
+            (Some(ErrorString::Ident(ident)), None)
+        },
+
+        ParseErrorKind::Basic(BasicParseErrorKind::UnexpectedToken(token)) |
+        ParseErrorKind::Custom(StyleParseErrorKind::ValueError(
+            ValueParseErrorKind::InvalidColor(token),
+        )) => (Some(ErrorString::UnexpectedToken(token)), None),
+
+        ParseErrorKind::Custom(StyleParseErrorKind::SelectorError(err)) => match err {
+            SelectorParseErrorKind::UnexpectedTokenInAttributeSelector(t) |
+            SelectorParseErrorKind::BadValueInAttr(t) |
+            SelectorParseErrorKind::ExpectedBarInAttr(t) |
+            SelectorParseErrorKind::NoQualifiedNameInAttributeSelector(t) |
+            SelectorParseErrorKind::InvalidQualNameInAttr(t) |
+            SelectorParseErrorKind::ExplicitNamespaceUnexpectedToken(t) |
+            SelectorParseErrorKind::PseudoElementExpectedIdent(t) |
+            SelectorParseErrorKind::NoIdentForPseudo(t) |
+            SelectorParseErrorKind::ClassNeedsIdent(t) |
+            SelectorParseErrorKind::PseudoElementExpectedColon(t) => {
+                (None, Some(ErrorString::UnexpectedToken(t)))
+            },
+            SelectorParseErrorKind::ExpectedNamespace(namespace) => {
+                (None, Some(ErrorString::Ident(namespace)))
+            },
+            SelectorParseErrorKind::UnsupportedPseudoClassOrElement(p) => {
+                (None, Some(ErrorString::Ident(p)))
+            },
+            SelectorParseErrorKind::EmptySelector | SelectorParseErrorKind::DanglingCombinator => {
+                (None, None)
+            },
+            err => match extract_error_param(ParseErrorKind::Custom(
+                StyleParseErrorKind::SelectorError(err),
+            )) {
+                Some(e) => (Some(e), None),
+                None => return None,
+            },
+        },
+        err => match extract_error_param(err) {
+            Some(e) => (Some(e), None),
+            None => return None,
+        },
+    };
+    Some(ErrorParams {
+        main_param: main,
+        prefix_param: prefix,
+    })
+}
+
+impl<'a> ErrorHelpers<'a> for ContextualParseError<'a> {
+    fn error_data(self) -> (CowRcStr<'a>, ErrorKind<'a>) {
+        match self {
+            ContextualParseError::UnsupportedPropertyDeclaration(s, err, _) |
+            ContextualParseError::UnsupportedPropertyDescriptor(s, err) |
+            ContextualParseError::UnsupportedFontFaceDescriptor(s, err) |
+            ContextualParseError::UnsupportedFontFeatureValuesDescriptor(s, err) |
+            ContextualParseError::UnsupportedFontPaletteValuesDescriptor(s, err) |
+            ContextualParseError::InvalidKeyframeRule(s, err) |
+            ContextualParseError::InvalidFontFeatureValuesRule(s, err) |
+            ContextualParseError::UnsupportedKeyframePropertyDeclaration(s, err) |
+            ContextualParseError::InvalidRule(s, err) |
+            ContextualParseError::UnsupportedRule(s, err) |
+            ContextualParseError::UnsupportedViewportDescriptorDeclaration(s, err) |
+            ContextualParseError::UnsupportedCounterStyleDescriptorDeclaration(s, err) |
+            ContextualParseError::InvalidMediaRule(s, err) |
+            ContextualParseError::UnsupportedValue(s, err) => (s.into(), err.kind),
+            ContextualParseError::NeverMatchingHostSelector(s) |
+            ContextualParseError::InvalidCounterStyleWithoutSymbols(s) |
+            ContextualParseError::InvalidCounterStyleNotEnoughSymbols(s) => (
+                s.into(),
+                ParseErrorKind::Custom(StyleParseErrorKind::UnspecifiedError.into()),
+            ),
+            ContextualParseError::InvalidCounterStyleWithoutAdditiveSymbols |
+            ContextualParseError::InvalidCounterStyleExtendsWithSymbols |
+            ContextualParseError::InvalidCounterStyleExtendsWithAdditiveSymbols => (
+                "".into(),
+                ParseErrorKind::Custom(StyleParseErrorKind::UnspecifiedError.into()),
+            ),
+        }
+    }
+
+    fn error_params(self) -> ErrorParams<'a> {
+        let (s, error) = self.error_data();
+        extract_error_params(error).unwrap_or_else(|| ErrorParams {
+            main_param: Some(ErrorString::Snippet(s)),
+            prefix_param: None,
+        })
+    }
+
+    fn selectors(&self) -> &'a [SelectorList<SelectorImpl>] {
+        match *self {
+            ContextualParseError::UnsupportedPropertyDeclaration(_, _, selectors) => selectors,
+            _ => &[],
+        }
+    }
+
+    fn to_gecko_message(&self) -> (Option<&'static CStr>, &'static CStr, Action) {
+        let (msg, action): (&CStr, Action) = match *self {
+            ContextualParseError::UnsupportedPropertyDeclaration(
+                _,
+                ParseError {
+                    kind: ParseErrorKind::Basic(BasicParseErrorKind::UnexpectedToken(_)),
+                    ..
+                },
+                _,
+            ) |
+            ContextualParseError::UnsupportedPropertyDeclaration(
+                _,
+                ParseError {
+                    kind: ParseErrorKind::Basic(BasicParseErrorKind::AtRuleInvalid(_)),
+                    ..
+                },
+                _,
+            ) => (cstr!("PEParseDeclarationDeclExpected"), Action::Skip),
+            ContextualParseError::UnsupportedPropertyDeclaration(
+                _,
+                ParseError {
+                    kind: ParseErrorKind::Custom(ref err),
+                    ..
+                },
+                _,
+            ) => match *err {
+                StyleParseErrorKind::InvalidColor(_, _) => {
+                    return (
+                        Some(cstr!("PEColorNotColor")),
+                        cstr!("PEValueParsingError"),
+                        Action::Drop,
+                    );
+                },
+                StyleParseErrorKind::InvalidFilter(_, _) => {
+                    return (
+                        Some(cstr!("PEExpectedNoneOrURLOrFilterFunction")),
+                        cstr!("PEValueParsingError"),
+                        Action::Drop,
+                    );
+                },
+                StyleParseErrorKind::OtherInvalidValue(_) => {
+                    (cstr!("PEValueParsingError"), Action::Drop)
+                },
+                _ => (cstr!("PEUnknownProperty"), Action::Drop),
+            },
+            ContextualParseError::UnsupportedPropertyDeclaration(..) => {
+                (cstr!("PEUnknownProperty"), Action::Drop)
+            },
+            ContextualParseError::UnsupportedFontFaceDescriptor(..) => {
+                (cstr!("PEUnknownFontDesc"), Action::Skip)
+            },
+            ContextualParseError::InvalidKeyframeRule(..) => {
+                (cstr!("PEKeyframeBadName"), Action::Nothing)
+            },
+            ContextualParseError::UnsupportedKeyframePropertyDeclaration(..) => {
+                (cstr!("PEBadSelectorKeyframeRuleIgnored"), Action::Nothing)
+            },
+            ContextualParseError::InvalidRule(
+                _,
+                ParseError {
+                    kind:
+                        ParseErrorKind::Custom(StyleParseErrorKind::UnexpectedTokenWithinNamespace(_)),
+                    ..
+                },
+            ) => (cstr!("PEAtNSUnexpected"), Action::Nothing),
+            ContextualParseError::InvalidRule(
+                _,
+                ParseError {
+                    kind: ParseErrorKind::Custom(StyleParseErrorKind::DisallowedImportRule),
+                    ..
+                },
+            ) => (cstr!("PEDisallowedImportRule"), Action::Nothing),
+            ContextualParseError::InvalidRule(
+                _,
+                ParseError {
+                    kind: ParseErrorKind::Basic(BasicParseErrorKind::AtRuleInvalid(_)),
+                    ..
+                },
+            ) => (cstr!("PEUnknownAtRule"), Action::Nothing),
+            ContextualParseError::InvalidRule(_, ref err) => {
+                let prefix = match err.kind {
+                    ParseErrorKind::Custom(StyleParseErrorKind::SelectorError(ref err)) => {
+                        match *err {
+                            SelectorParseErrorKind::UnexpectedTokenInAttributeSelector(_) => {
+                                Some(cstr!("PEAttSelUnexpected"))
+                            },
+                            SelectorParseErrorKind::ExpectedBarInAttr(_) => {
+                                Some(cstr!("PEAttSelNoBar"))
+                            },
+                            SelectorParseErrorKind::BadValueInAttr(_) => {
+                                Some(cstr!("PEAttSelBadValue"))
+                            },
+                            SelectorParseErrorKind::NoQualifiedNameInAttributeSelector(_) => {
+                                Some(cstr!("PEAttributeNameOrNamespaceExpected"))
+                            },
+                            SelectorParseErrorKind::InvalidQualNameInAttr(_) => {
+                                Some(cstr!("PEAttributeNameExpected"))
+                            },
+                            SelectorParseErrorKind::ExplicitNamespaceUnexpectedToken(_) => {
+                                Some(cstr!("PETypeSelNotType"))
+                            },
+                            SelectorParseErrorKind::ExpectedNamespace(_) => {
+                                Some(cstr!("PEUnknownNamespacePrefix"))
+                            },
+                            SelectorParseErrorKind::EmptySelector => {
+                                Some(cstr!("PESelectorGroupNoSelector"))
+                            },
+                            SelectorParseErrorKind::DanglingCombinator => {
+                                Some(cstr!("PESelectorGroupExtraCombinator"))
+                            },
+                            SelectorParseErrorKind::UnsupportedPseudoClassOrElement(_) => {
+                                Some(cstr!("PEPseudoSelUnknown"))
+                            },
+                            SelectorParseErrorKind::PseudoElementExpectedColon(_) => {
+                                Some(cstr!("PEPseudoSelEndOrUserActionPC"))
+                            },
+                            SelectorParseErrorKind::NoIdentForPseudo(_) => {
+                                Some(cstr!("PEPseudoClassArgNotIdent"))
+                            },
+                            SelectorParseErrorKind::PseudoElementExpectedIdent(_) => {
+                                Some(cstr!("PEPseudoSelBadName"))
+                            },
+                            SelectorParseErrorKind::ClassNeedsIdent(_) => {
+                                Some(cstr!("PEClassSelNotIdent"))
+                            },
+                            _ => None,
+                        }
+                    },
+                    _ => None,
+                };
+                return (prefix, cstr!("PEBadSelectorRSIgnored"), Action::Nothing);
+            },
+            ContextualParseError::InvalidMediaRule(_, ref err) => {
+                let err: &CStr = match err.kind {
+                    ParseErrorKind::Custom(StyleParseErrorKind::MediaQueryExpectedFeatureName(
+                        ..,
+                    )) => cstr!("PEMQExpectedFeatureName"),
+                    ParseErrorKind::Custom(StyleParseErrorKind::MediaQueryExpectedFeatureValue) => {
+                        cstr!("PEMQExpectedFeatureValue")
+                    },
+                    ParseErrorKind::Custom(StyleParseErrorKind::MediaQueryUnexpectedOperator) => {
+                        cstr!("PEMQUnexpectedOperator")
+                    },
+                    ParseErrorKind::Custom(StyleParseErrorKind::RangedExpressionWithNoValue) => {
+                        cstr!("PEMQNoMinMaxWithoutValue")
+                    },
+                    _ => cstr!("PEMQUnexpectedToken"),
+                };
+                (err, Action::Nothing)
+            },
+            ContextualParseError::UnsupportedRule(..) => (cstr!("PEDeclDropped"), Action::Nothing),
+            ContextualParseError::NeverMatchingHostSelector(..) => {
+                (cstr!("PENeverMatchingHostSelector"), Action::Nothing)
+            },
+            ContextualParseError::UnsupportedViewportDescriptorDeclaration(..) |
+            ContextualParseError::UnsupportedCounterStyleDescriptorDeclaration(..) |
+            ContextualParseError::InvalidCounterStyleWithoutSymbols(..) |
+            ContextualParseError::InvalidCounterStyleNotEnoughSymbols(..) |
+            ContextualParseError::InvalidCounterStyleWithoutAdditiveSymbols |
+            ContextualParseError::InvalidCounterStyleExtendsWithSymbols |
+            ContextualParseError::InvalidCounterStyleExtendsWithAdditiveSymbols |
+            ContextualParseError::UnsupportedPropertyDescriptor(..) |
+            ContextualParseError::UnsupportedFontFeatureValuesDescriptor(..) |
+            ContextualParseError::UnsupportedFontPaletteValuesDescriptor(..) |
+            ContextualParseError::InvalidFontFeatureValuesRule(..) => {
+                (cstr!("PEUnknownAtRule"), Action::Skip)
+            },
+            ContextualParseError::UnsupportedValue(_, ParseError { ref kind, .. }) => {
+                match *kind {
+                    ParseErrorKind::Custom(StyleParseErrorKind::ValueError(
+                        ValueParseErrorKind::InvalidColor(..),
+                    )) => (cstr!("PEColorNotColor"), Action::Nothing),
+                    ParseErrorKind::Custom(StyleParseErrorKind::PropertySyntaxField(ref kind)) => {
+                        let name = match kind {
+                            PropertySyntaxParseError::EmptyInput => {
+                                cstr!("PEPRSyntaxFieldEmptyInput")
+                            },
+                            PropertySyntaxParseError::ExpectedPipeBetweenComponents => {
+                                cstr!("PEPRSyntaxFieldExpectedPipe")
+                            },
+                            PropertySyntaxParseError::InvalidNameStart => {
+                                cstr!("PEPRSyntaxFieldInvalidNameStart")
+                            },
+                            PropertySyntaxParseError::InvalidName => {
+                                cstr!("PEPRSyntaxFieldInvalidName")
+                            },
+                            PropertySyntaxParseError::UnclosedDataTypeName => {
+                                cstr!("PEPRSyntaxFieldUnclosedDataTypeName")
+                            },
+                            PropertySyntaxParseError::UnexpectedEOF => {
+                                cstr!("PEPRSyntaxFieldUnexpectedEOF")
+                            },
+                            PropertySyntaxParseError::UnknownDataTypeName => {
+                                cstr!("PEPRSyntaxFieldUnknownDataTypeName")
+                            },
+                        };
+                        (name, Action::Nothing)
+                    },
+                    _ => {
+                        // Not the best error message, since we weren't parsing
+                        // a declaration, just a value. But we don't produce
+                        // UnsupportedValue errors other than InvalidColors
+                        // currently.
+                        debug_assert!(false, "should use a more specific error message");
+                        (cstr!("PEDeclDropped"), Action::Nothing)
+                    },
+                }
+            },
+        };
+        (None, msg, action)
+    }
+}
+
+impl ErrorReporter {
+    pub fn report(&self, location: SourceLocation, error: ContextualParseError) {
+        let (pre, name, action) = error.to_gecko_message();
+        let suffix = match action {
+            Action::Nothing => ptr::null(),
+            Action::Skip => cstr!("PEDeclSkipped").as_ptr(),
+            Action::Drop => cstr!("PEDeclDropped").as_ptr(),
+        };
+        let selectors = error.selectors();
+        let desugared_selector_list = match selectors.len() {
+            0 => None,
+            1 => Some(selectors[0].to_css_string()),
+            _ => {
+                let mut desugared = selectors.last().unwrap().clone();
+                for parent in selectors.iter().rev().skip(1) {
+                    desugared = desugared.replace_parent_selector(&parent);
+                }
+                Some(desugared.to_css_string())
+            },
+        };
+        let selector_list_ptr = desugared_selector_list
+            .as_ref()
+            .map_or(ptr::null(), |s| s.as_ptr()) as *const _;
+        let params = error.error_params();
+        let param = params.main_param;
+        let pre_param = params.prefix_param;
+        let param = param.map(|p| p.into_str());
+        let pre_param = pre_param.map(|p| p.into_str());
+        let param_ptr = param.as_ref().map_or(ptr::null(), |p| p.as_ptr());
+        let pre_param_ptr = pre_param.as_ref().map_or(ptr::null(), |p| p.as_ptr());
+        // The CSS source text is unused and will be removed in bug 1381188.
+        let source = "";
+        unsafe {
+            bindings::Gecko_ReportUnexpectedCSSError(
+                self.window_id,
+                self.uri,
+                name.as_ptr() as *const _,
+                param_ptr as *const _,
+                param.as_ref().map_or(0, |p| p.len()) as u32,
+                pre.map_or(ptr::null(), |p| p.as_ptr()) as *const _,
+                pre_param_ptr as *const _,
+                pre_param.as_ref().map_or(0, |p| p.len()) as u32,
+                suffix as *const _,
+                source.as_ptr() as *const _,
+                source.len() as u32,
+                selector_list_ptr,
+                desugared_selector_list
+                    .as_ref()
+                    .map_or(0, |string| string.len()) as u32,
+                location.line,
+                location.column,
+            );
+        }
+    }
+}
+
+impl ParseErrorReporter for ErrorReporter {
+    fn report_error(
+        &self,
+        _url: &UrlExtraData,
+        location: SourceLocation,
+        error: ContextualParseError,
+    ) {
+        self.report(location, error)
+    }
+}
diff --git a/servo/ports/geckolib/glue.rs b/servo/ports/geckolib/glue.rs
new file mode 100644
index 0000000000..a6c4ef1262
--- /dev/null
+++ b/servo/ports/geckolib/glue.rs
@@ -0,0 +1,8921 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use super::error_reporter::ErrorReporter;
+use super::stylesheet_loader::{AsyncStylesheetParser, StylesheetLoader};
+use bincode::{deserialize, serialize};
+use cssparser::ToCss as ParserToCss;
+use cssparser::{Parser, ParserInput, SourceLocation, UnicodeRange};
+use dom::{DocumentState, ElementState};
+use malloc_size_of::MallocSizeOfOps;
+use nsstring::{nsCString, nsString};
+use selectors::matching::{ElementSelectorFlags, MatchingForInvalidation, SelectorCaches};
+use selectors::{Element, OpaqueElement};
+use servo_arc::{Arc, ArcBorrow};
+use smallvec::SmallVec;
+use style::custom_properties::DeferFontRelativeCustomPropertyResolution;
+use std::collections::BTreeSet;
+use std::fmt::Write;
+use std::iter;
+use std::os::raw::c_void;
+use std::ptr;
+use style::color::mix::ColorInterpolationMethod;
+use style::color::{AbsoluteColor, ColorSpace};
+use style::computed_value_flags::ComputedValueFlags;
+use style::context::ThreadLocalStyleContext;
+use style::context::{CascadeInputs, QuirksMode, SharedStyleContext, StyleContext};
+use style::counter_style;
+use style::data::{self, ElementStyles};
+use style::dom::{ShowSubtreeData, TDocument, TElement, TNode};
+use style::driver;
+use style::error_reporting::{ParseErrorReporter, SelectorWarningKind};
+use style::font_face::{self, FontFaceSourceFormat, FontFaceSourceListComponent, Source};
+use style::gecko::arc_types::{
+    LockedCounterStyleRule, LockedCssRules, LockedDeclarationBlock, LockedFontFaceRule,
+    LockedImportRule, LockedKeyframe, LockedKeyframesRule, LockedMediaList, LockedPageRule,
+    LockedStyleRule,
+};
+use style::gecko::data::{
+    AuthorStyles, GeckoStyleSheet, PerDocumentStyleData, PerDocumentStyleDataImpl,
+};
+use style::gecko::restyle_damage::GeckoRestyleDamage;
+use style::gecko::selector_parser::{NonTSPseudoClass, PseudoElement};
+use style::gecko::snapshot_helpers::classes_changed;
+use style::gecko::traversal::RecalcStyleOnly;
+use style::gecko::url;
+use style::gecko::wrapper::{
+    slow_selector_flags_from_node_selector_flags, GeckoElement, GeckoNode,
+};
+use style::gecko_bindings::bindings;
+use style::gecko_bindings::bindings::nsACString;
+use style::gecko_bindings::bindings::nsAString;
+use style::gecko_bindings::bindings::Gecko_AddPropertyToSet;
+use style::gecko_bindings::bindings::Gecko_AppendPropertyValuePair;
+use style::gecko_bindings::bindings::Gecko_ConstructFontFeatureValueSet;
+use style::gecko_bindings::bindings::Gecko_ConstructFontPaletteValueSet;
+use style::gecko_bindings::bindings::Gecko_GetOrCreateFinalKeyframe;
+use style::gecko_bindings::bindings::Gecko_GetOrCreateInitialKeyframe;
+use style::gecko_bindings::bindings::Gecko_GetOrCreateKeyframeAtStart;
+use style::gecko_bindings::bindings::Gecko_HaveSeenPtr;
+use style::gecko_bindings::structs;
+use style::gecko_bindings::structs::gfx::FontPaletteValueSet;
+use style::gecko_bindings::structs::gfxFontFeatureValueSet;
+use style::gecko_bindings::structs::ipc::ByteBuf;
+use style::gecko_bindings::structs::nsAtom;
+use style::gecko_bindings::structs::nsCSSCounterDesc;
+use style::gecko_bindings::structs::nsCSSFontDesc;
+use style::gecko_bindings::structs::nsCSSPropertyID;
+use style::gecko_bindings::structs::nsChangeHint;
+use style::gecko_bindings::structs::nsCompatibility;
+use style::gecko_bindings::structs::nsStyleTransformMatrix::MatrixTransformOperator;
+use style::gecko_bindings::structs::nsTArray;
+use style::gecko_bindings::structs::nsresult;
+use style::gecko_bindings::structs::CallerType;
+use style::gecko_bindings::structs::CompositeOperation;
+use style::gecko_bindings::structs::DeclarationBlockMutationClosure;
+use style::gecko_bindings::structs::GeckoFontMetrics;
+use style::gecko_bindings::structs::IterationCompositeOperation;
+use style::gecko_bindings::structs::Loader;
+use style::gecko_bindings::structs::LoaderReusableStyleSheets;
+use style::gecko_bindings::structs::MallocSizeOf as GeckoMallocSizeOf;
+use style::gecko_bindings::structs::OriginFlags;
+use style::gecko_bindings::structs::PropertyValuePair;
+use style::gecko_bindings::structs::PseudoStyleType;
+use style::gecko_bindings::structs::SeenPtrs;
+use style::gecko_bindings::structs::ServoElementSnapshotTable;
+use style::gecko_bindings::structs::ServoStyleSetSizes;
+use style::gecko_bindings::structs::ServoTraversalFlags;
+use style::gecko_bindings::structs::SheetLoadData;
+use style::gecko_bindings::structs::SheetLoadDataHolder;
+use style::gecko_bindings::structs::SheetParsingMode;
+use style::gecko_bindings::structs::StyleRuleInclusion;
+use style::gecko_bindings::structs::StyleSheet as DomStyleSheet;
+use style::gecko_bindings::structs::URLExtraData;
+use style::gecko_bindings::structs::{nsINode as RawGeckoNode, Element as RawGeckoElement};
+use style::gecko_bindings::sugar::ownership::Strong;
+use style::gecko_bindings::sugar::refptr::RefPtr;
+use style::global_style_data::{
+    GlobalStyleData, PlatformThreadHandle, StyleThreadPool, GLOBAL_STYLE_DATA, STYLE_THREAD_POOL,
+};
+use style::invalidation::element::element_wrapper::{ElementSnapshot, ElementWrapper};
+use style::invalidation::element::invalidation_map::{
+    RelativeSelectorInvalidationMap, TSStateForInvalidation,
+};
+use style::invalidation::element::invalidator::{InvalidationResult, SiblingTraversalMap};
+use style::invalidation::element::relative_selector::{
+    DomMutationOperation, RelativeSelectorDependencyCollector, RelativeSelectorInvalidator,
+};
+use style::invalidation::element::restyle_hints::RestyleHint;
+use style::invalidation::stylesheets::RuleChangeKind;
+use style::media_queries::MediaList;
+use style::parser::{Parse, ParserContext};
+#[cfg(feature = "gecko_debug")]
+use style::properties::LonghandIdSet;
+use style::properties::{
+    animated_properties::{AnimationValue, AnimationValueMap},
+    parse_one_declaration_into, parse_style_attribute, ComputedValues, CountedUnknownProperty,
+    Importance, LonghandId, NonCustomPropertyId, OwnedPropertyDeclarationId,
+    PropertyDeclarationBlock, PropertyDeclarationId, PropertyDeclarationIdSet, PropertyId,
+    ShorthandId, SourcePropertyDeclaration, StyleBuilder,
+};
+use style::properties_and_values::registry::{PropertyRegistration, PropertyRegistrationData};
+use style::properties_and_values::rule::Inherits as PropertyInherits;
+use style::rule_cache::RuleCacheConditions;
+use style::rule_tree::StrongRuleNode;
+use style::selector_parser::PseudoElementCascadeType;
+use style::shared_lock::{
+    Locked, SharedRwLock, SharedRwLockReadGuard, StylesheetGuards, ToCssWithGuard,
+};
+use style::string_cache::{Atom, WeakAtom};
+use style::style_adjuster::StyleAdjuster;
+use style::stylesheets::container_rule::ContainerSizeQuery;
+use style::stylesheets::import_rule::{ImportLayer, ImportSheet};
+use style::stylesheets::keyframes_rule::{Keyframe, KeyframeSelector, KeyframesStepValue};
+use style::stylesheets::supports_rule::parse_condition_or_declaration;
+use style::stylesheets::{
+    AllowImportRules, ContainerRule, CounterStyleRule, CssRule, CssRuleType, CssRuleTypes,
+    CssRules, CssRulesHelpers, DocumentRule, FontFaceRule, FontFeatureValuesRule,
+    FontPaletteValuesRule, ImportRule, KeyframesRule, LayerBlockRule, LayerStatementRule,
+    MediaRule, NamespaceRule, Origin, OriginSet, PagePseudoClassFlags, PageRule, PropertyRule,
+    SanitizationData, SanitizationKind, StyleRule, StylesheetContents,
+    StylesheetLoader as StyleStylesheetLoader, SupportsRule, UrlExtraData,
+};
+use style::stylist::{add_size_of_ua_cache, AuthorStylesEnabled, RuleInclusion, Stylist};
+use style::thread_state;
+use style::traversal::resolve_style;
+use style::traversal::DomTraversal;
+use style::traversal_flags::{self, TraversalFlags};
+use style::use_counters::UseCounters;
+use style::values::animated::{Animate, Procedure, ToAnimatedZero};
+use style::values::computed::easing::ComputedTimingFunction;
+use style::values::computed::effects::Filter;
+use style::values::computed::font::{
+    FamilyName, FontFamily, FontFamilyList, FontStretch, FontStyle, FontWeight, GenericFontFamily,
+};
+use style::values::computed::{self, Context, ToComputedValue};
+use style::values::distance::ComputeSquaredDistance;
+use style::values::generics::color::ColorMixFlags;
+use style::values::generics::easing::BeforeFlag;
+use style::values::specified::gecko::IntersectionObserverRootMargin;
+use style::values::specified::source_size_list::SourceSizeList;
+use style::values::specified::{AbsoluteLength, NoCalcLength};
+use style::values::{specified, AtomIdent, CustomIdent, KeyframesName};
+use style_traits::{CssWriter, ParseError, ParsingMode, ToCss};
+use thin_vec::ThinVec;
+use to_shmem::SharedMemoryBuilder;
+
+trait ClosureHelper {
+    fn invoke(&self, property_id: Option<NonCustomPropertyId>);
+}
+
+impl ClosureHelper for DeclarationBlockMutationClosure {
+    #[inline]
+    fn invoke(&self, property_id: Option<NonCustomPropertyId>) {
+        if let Some(function) = self.function.as_ref() {
+            let gecko_prop_id = match property_id {
+                Some(p) => p.to_nscsspropertyid(),
+                None => nsCSSPropertyID::eCSSPropertyExtra_variable,
+            };
+            unsafe { function(self.data, gecko_prop_id) }
+        }
+    }
+}
+
+/*
+ * For Gecko->Servo function calls, we need to redeclare the same signature that was declared in
+ * the C header in Gecko. In order to catch accidental mismatches, we run rust-bindgen against
+ * those signatures as well, giving us a second declaration of all the Servo_* functions in this
+ * crate. If there's a mismatch, LLVM will assert and abort, which is a rather awful thing to
+ * depend on but good enough for our purposes.
+ */
+
+// A dummy url data for where we don't pass url data in.
+static mut DUMMY_URL_DATA: *mut URLExtraData = 0 as *mut _;
+static mut DUMMY_CHROME_URL_DATA: *mut URLExtraData = 0 as *mut _;
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Initialize(
+    dummy_url_data: *mut URLExtraData,
+    dummy_chrome_url_data: *mut URLExtraData,
+) {
+    use style::gecko_bindings::sugar::origin_flags;
+
+    // Pretend that we're a Servo Layout thread, to make some assertions happy.
+    thread_state::initialize(thread_state::ThreadState::LAYOUT);
+
+    // Perform some debug-only runtime assertions.
+    origin_flags::assert_flags_match();
+    traversal_flags::assert_traversal_flags_match();
+    specified::font::assert_variant_east_asian_matches();
+    specified::font::assert_variant_ligatures_matches();
+
+    DUMMY_URL_DATA = dummy_url_data;
+    DUMMY_CHROME_URL_DATA = dummy_chrome_url_data;
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Shutdown() {
+    DUMMY_URL_DATA = ptr::null_mut();
+    DUMMY_CHROME_URL_DATA = ptr::null_mut();
+    Stylist::shutdown();
+    url::shutdown();
+}
+
+#[inline(always)]
+unsafe fn dummy_url_data() -> &'static UrlExtraData {
+    UrlExtraData::from_ptr_ref(&DUMMY_URL_DATA)
+}
+
+#[allow(dead_code)]
+fn is_main_thread() -> bool {
+    unsafe { bindings::Gecko_IsMainThread() }
+}
+
+#[allow(dead_code)]
+fn is_dom_worker_thread() -> bool {
+    unsafe { bindings::Gecko_IsDOMWorkerThread() }
+}
+
+thread_local! {
+    /// Thread-local style data for DOM workers
+    static DOM_WORKER_RWLOCK: SharedRwLock = SharedRwLock::new();
+}
+
+#[allow(dead_code)]
+fn is_in_servo_traversal() -> bool {
+    unsafe { bindings::Gecko_IsInServoTraversal() }
+}
+
+fn create_shared_context<'a>(
+    global_style_data: &GlobalStyleData,
+    guard: &'a SharedRwLockReadGuard,
+    stylist: &'a Stylist,
+    traversal_flags: TraversalFlags,
+    snapshot_map: &'a ServoElementSnapshotTable,
+) -> SharedStyleContext<'a> {
+    SharedStyleContext {
+        stylist: &stylist,
+        visited_styles_enabled: stylist.device().visited_styles_enabled(),
+        options: global_style_data.options.clone(),
+        guards: StylesheetGuards::same(guard),
+        current_time_for_animations: 0.0, // Unused for Gecko, at least for now.
+        traversal_flags,
+        snapshot_map,
+    }
+}
+
+fn traverse_subtree(
+    element: GeckoElement,
+    global_style_data: &GlobalStyleData,
+    per_doc_data: &PerDocumentStyleDataImpl,
+    guard: &SharedRwLockReadGuard,
+    traversal_flags: TraversalFlags,
+    snapshots: &ServoElementSnapshotTable,
+) {
+    let shared_style_context = create_shared_context(
+        &global_style_data,
+        &guard,
+        &per_doc_data.stylist,
+        traversal_flags,
+        snapshots,
+    );
+
+    let token = RecalcStyleOnly::pre_traverse(element, &shared_style_context);
+
+    if !token.should_traverse() {
+        return;
+    }
+
+    debug!("Traversing subtree from {:?}", element);
+
+    let thread_pool_holder = &*STYLE_THREAD_POOL;
+    let pool;
+    let thread_pool = if traversal_flags.contains(TraversalFlags::ParallelTraversal) {
+        pool = thread_pool_holder.pool();
+        pool.as_ref()
+    } else {
+        None
+    };
+
+    let traversal = RecalcStyleOnly::new(shared_style_context);
+    driver::traverse_dom(&traversal, token, thread_pool);
+}
+
+/// Traverses the subtree rooted at `root` for restyling.
+///
+/// Returns whether the root was restyled. Whether anything else was restyled or
+/// not can be inferred from the dirty bits in the rest of the tree.
+#[no_mangle]
+pub extern "C" fn Servo_TraverseSubtree(
+    root: &RawGeckoElement,
+    raw_data: &PerDocumentStyleData,
+    snapshots: *const ServoElementSnapshotTable,
+    raw_flags: ServoTraversalFlags,
+) -> bool {
+    let traversal_flags = TraversalFlags::from_bits_retain(raw_flags);
+    debug_assert!(!snapshots.is_null());
+
+    let element = GeckoElement(root);
+
+    debug!("Servo_TraverseSubtree (flags={:?})", traversal_flags);
+    debug!("{:?}", ShowSubtreeData(element.as_node()));
+
+    if cfg!(debug_assertions) {
+        if let Some(parent) = element.traversal_parent() {
+            let data = parent
+                .borrow_data()
+                .expect("Styling element with unstyled parent");
+            assert!(
+                !data.styles.is_display_none(),
+                "Styling element with display: none parent"
+            );
+        }
+    }
+
+    let needs_animation_only_restyle =
+        element.has_animation_only_dirty_descendants() || element.has_animation_restyle_hints();
+
+    let per_doc_data = raw_data.borrow();
+    debug_assert!(!per_doc_data.stylist.stylesheets_have_changed());
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    let was_initial_style = !element.has_data();
+
+    if needs_animation_only_restyle {
+        debug!(
+            "Servo_TraverseSubtree doing animation-only restyle (aodd={})",
+            element.has_animation_only_dirty_descendants()
+        );
+        traverse_subtree(
+            element,
+            &global_style_data,
+            &per_doc_data,
+            &guard,
+            traversal_flags | TraversalFlags::AnimationOnly,
+            unsafe { &*snapshots },
+        );
+    }
+
+    traverse_subtree(
+        element,
+        &global_style_data,
+        &per_doc_data,
+        &guard,
+        traversal_flags,
+        unsafe { &*snapshots },
+    );
+
+    debug!(
+        "Servo_TraverseSubtree complete (dd={}, aodd={}, lfcd={}, lfc={}, data={:?})",
+        element.has_dirty_descendants(),
+        element.has_animation_only_dirty_descendants(),
+        element.descendants_need_frames(),
+        element.needs_frame(),
+        element.borrow_data().unwrap()
+    );
+
+    if was_initial_style {
+        debug_assert!(!element.borrow_data().unwrap().contains_restyle_data());
+        false
+    } else {
+        let element_was_restyled = element.borrow_data().unwrap().contains_restyle_data();
+        element_was_restyled
+    }
+}
+
+/// Checks whether the rule tree has crossed its threshold for unused nodes, and
+/// if so, frees them.
+#[no_mangle]
+pub extern "C" fn Servo_MaybeGCRuleTree(raw_data: &PerDocumentStyleData) {
+    let per_doc_data = raw_data.borrow_mut();
+    per_doc_data.stylist.rule_tree().maybe_gc();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_Interpolate(
+    from: &AnimationValue,
+    to: &AnimationValue,
+    progress: f64,
+) -> Strong<AnimationValue> {
+    if let Ok(value) = from.animate(to, Procedure::Interpolate { progress }) {
+        Arc::new(value).into()
+    } else {
+        Strong::null()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_IsInterpolable(
+    from: &AnimationValue,
+    to: &AnimationValue,
+) -> bool {
+    from.interpolable_with(to)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_Add(
+    a: &AnimationValue,
+    b: &AnimationValue,
+) -> Strong<AnimationValue> {
+    if let Ok(value) = a.animate(b, Procedure::Add) {
+        Arc::new(value).into()
+    } else {
+        Strong::null()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_Accumulate(
+    a: &AnimationValue,
+    b: &AnimationValue,
+    count: u64,
+) -> Strong<AnimationValue> {
+    if let Ok(value) = a.animate(b, Procedure::Accumulate { count }) {
+        Arc::new(value).into()
+    } else {
+        Strong::null()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_GetZeroValue(
+    value_to_match: &AnimationValue,
+) -> Strong<AnimationValue> {
+    if let Ok(zero_value) = value_to_match.to_animated_zero() {
+        Arc::new(zero_value).into()
+    } else {
+        Strong::null()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValues_ComputeDistance(
+    from: &AnimationValue,
+    to: &AnimationValue,
+) -> f64 {
+    // If compute_squared_distance() failed, this function will return negative value
+    // in order to check whether we support the specified paced animation values.
+    from.compute_squared_distance(to).map_or(-1.0, |d| d.sqrt())
+}
+
+/// Compute one of the endpoints for the interpolation interval, compositing it with the
+/// underlying value if needed.
+/// An None returned value means, "Just use endpoint_value as-is."
+/// It is the responsibility of the caller to ensure that |underlying_value| is provided
+/// when it will be used.
+fn composite_endpoint(
+    endpoint_value: Option<&AnimationValue>,
+    composite: CompositeOperation,
+    underlying_value: Option<&AnimationValue>,
+) -> Option<AnimationValue> {
+    match endpoint_value {
+        Some(endpoint_value) => match composite {
+            CompositeOperation::Add => underlying_value
+                .expect("We should have an underlying_value")
+                .animate(endpoint_value, Procedure::Add)
+                .ok(),
+            CompositeOperation::Accumulate => underlying_value
+                .expect("We should have an underlying value")
+                .animate(endpoint_value, Procedure::Accumulate { count: 1 })
+                .ok(),
+            _ => None,
+        },
+        None => underlying_value.map(|v| v.clone()),
+    }
+}
+
+/// Accumulate one of the endpoints of the animation interval.
+/// A returned value of None means, "Just use endpoint_value as-is."
+fn accumulate_endpoint(
+    endpoint_value: Option<&AnimationValue>,
+    composited_value: Option<AnimationValue>,
+    last_value: &AnimationValue,
+    current_iteration: u64,
+) -> Option<AnimationValue> {
+    debug_assert!(
+        endpoint_value.is_some() || composited_value.is_some(),
+        "Should have a suitable value to use"
+    );
+
+    let count = current_iteration;
+    match composited_value {
+        Some(endpoint) => last_value
+            .animate(&endpoint, Procedure::Accumulate { count })
+            .ok()
+            .or(Some(endpoint)),
+        None => last_value
+            .animate(endpoint_value.unwrap(), Procedure::Accumulate { count })
+            .ok(),
+    }
+}
+
+/// Compose the animation segment. We composite it with the underlying_value and last_value if
+/// needed.
+/// The caller is responsible for providing an underlying value and last value
+/// in all situations where there are needed.
+fn compose_animation_segment(
+    segment: &structs::AnimationPropertySegment,
+    underlying_value: Option<&AnimationValue>,
+    last_value: Option<&AnimationValue>,
+    iteration_composite: IterationCompositeOperation,
+    current_iteration: u64,
+    total_progress: f64,
+    segment_progress: f64,
+) -> AnimationValue {
+    // Extract keyframe values.
+    let keyframe_from_value = unsafe { segment.mFromValue.mServo.mRawPtr.as_ref() };
+    let keyframe_to_value = unsafe { segment.mToValue.mServo.mRawPtr.as_ref() };
+    let mut composited_from_value = composite_endpoint(
+        keyframe_from_value,
+        segment.mFromComposite,
+        underlying_value,
+    );
+    let mut composited_to_value =
+        composite_endpoint(keyframe_to_value, segment.mToComposite, underlying_value);
+
+    debug_assert!(
+        keyframe_from_value.is_some() || composited_from_value.is_some(),
+        "Should have a suitable from value to use"
+    );
+    debug_assert!(
+        keyframe_to_value.is_some() || composited_to_value.is_some(),
+        "Should have a suitable to value to use"
+    );
+
+    // Apply iteration composite behavior.
+    if iteration_composite == IterationCompositeOperation::Accumulate && current_iteration > 0 {
+        let last_value = last_value
+            .unwrap_or_else(|| underlying_value.expect("Should have a valid underlying value"));
+
+        composited_from_value = accumulate_endpoint(
+            keyframe_from_value,
+            composited_from_value,
+            last_value,
+            current_iteration,
+        );
+        composited_to_value = accumulate_endpoint(
+            keyframe_to_value,
+            composited_to_value,
+            last_value,
+            current_iteration,
+        );
+    }
+
+    // Use the composited value if there is one, otherwise, use the original keyframe value.
+    let from = composited_from_value
+        .as_ref()
+        .unwrap_or_else(|| keyframe_from_value.unwrap());
+    let to = composited_to_value
+        .as_ref()
+        .unwrap_or_else(|| keyframe_to_value.unwrap());
+
+    if segment.mToKey == segment.mFromKey {
+        return if total_progress < 0. {
+            from.clone()
+        } else {
+            to.clone()
+        };
+    }
+
+    match from.animate(
+        to,
+        Procedure::Interpolate {
+            progress: segment_progress,
+        },
+    ) {
+        Ok(value) => value,
+        _ => {
+            if segment_progress < 0.5 {
+                from.clone()
+            } else {
+                to.clone()
+            }
+        },
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComposeAnimationSegment(
+    segment: &structs::AnimationPropertySegment,
+    underlying_value: Option<&AnimationValue>,
+    last_value: Option<&AnimationValue>,
+    iteration_composite: IterationCompositeOperation,
+    progress: f64,
+    current_iteration: u64,
+) -> Strong<AnimationValue> {
+    let result = compose_animation_segment(
+        segment,
+        underlying_value,
+        last_value,
+        iteration_composite,
+        current_iteration,
+        progress,
+        progress,
+    );
+    Arc::new(result).into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationCompose(
+    value_map: &mut AnimationValueMap,
+    base_values: &structs::RawServoAnimationValueTable,
+    css_property: &structs::AnimatedPropertyID,
+    segment: &structs::AnimationPropertySegment,
+    last_segment: &structs::AnimationPropertySegment,
+    computed_timing: &structs::ComputedTiming,
+    iteration_composite: IterationCompositeOperation,
+) {
+    use style::gecko_bindings::bindings::Gecko_AnimationGetBaseStyle;
+    use style::gecko_bindings::bindings::Gecko_GetPositionInSegment;
+    use style::gecko_bindings::bindings::Gecko_GetProgressFromComputedTiming;
+
+    let property = match OwnedPropertyDeclarationId::from_gecko_animated_property_id(css_property) {
+        Some(property) if property.as_borrowed().is_animatable() => property,
+        _ => return,
+    };
+
+    // We will need an underlying value if either of the endpoints is null...
+    let need_underlying_value = segment.mFromValue.mServo.mRawPtr.is_null() ||
+                                segment.mToValue.mServo.mRawPtr.is_null() ||
+                                // ... or if they have a non-replace composite mode ...
+                                segment.mFromComposite != CompositeOperation::Replace ||
+                                segment.mToComposite != CompositeOperation::Replace ||
+                                // ... or if we accumulate onto the last value and it is null.
+                                (iteration_composite == IterationCompositeOperation::Accumulate &&
+                                 computed_timing.mCurrentIteration > 0 &&
+                                 last_segment.mToValue.mServo.mRawPtr.is_null());
+
+    // If either of the segment endpoints are null, get the underlying value to
+    // use from the current value in the values map (set by a lower-priority
+    // effect), or, if there is no current value, look up the cached base value
+    // for this property.
+    let underlying_value = if need_underlying_value {
+        let previous_composed_value = value_map.get(&property).map(|v| &*v);
+        previous_composed_value
+            .or_else(|| unsafe { Gecko_AnimationGetBaseStyle(base_values, css_property).as_ref() })
+    } else {
+        None
+    };
+
+    if need_underlying_value && underlying_value.is_none() {
+        warn!("Underlying value should be valid when we expect to use it");
+        return;
+    }
+
+    let last_value = unsafe { last_segment.mToValue.mServo.mRawPtr.as_ref() };
+    let progress = unsafe { Gecko_GetProgressFromComputedTiming(computed_timing) };
+    let position = if segment.mToKey == segment.mFromKey {
+        // Note: compose_animation_segment doesn't use this value
+        // if segment.mFromKey == segment.mToKey, so assigning |progress| directly is fine.
+        progress
+    } else {
+        unsafe { Gecko_GetPositionInSegment(segment, progress, computed_timing.mBeforeFlag) }
+    };
+
+    let result = compose_animation_segment(
+        segment,
+        underlying_value,
+        last_value,
+        iteration_composite,
+        computed_timing.mCurrentIteration,
+        progress,
+        position,
+    );
+    value_map.insert(property, result);
+}
+
+macro_rules! get_property_id_from_nscsspropertyid {
+    ($property_id: ident, $ret: expr) => {{
+        match PropertyId::from_nscsspropertyid($property_id) {
+            Some(property_id) => property_id,
+            None => {
+                return $ret;
+            },
+        }
+    }};
+}
+
+macro_rules! get_property_id_from_animatedpropertyid {
+    ($property_id: ident, $ret: expr) => {{
+        match PropertyId::from_gecko_animated_property_id($property_id) {
+            Some(property_id) => property_id,
+            None => {
+                return $ret;
+            },
+        }
+    }};
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_Serialize(
+    value: &AnimationValue,
+    property: &structs::AnimatedPropertyID,
+    raw_data: &PerDocumentStyleData,
+    buffer: &mut nsACString,
+) {
+    let uncomputed_value = value.uncompute();
+    let data = raw_data.borrow();
+    let rv = PropertyDeclarationBlock::with_one(uncomputed_value, Importance::Normal)
+        .single_value_to_css(
+            &get_property_id_from_animatedpropertyid!(property, ()),
+            buffer,
+            None,
+            &data.stylist,
+        );
+    debug_assert!(rv.is_ok());
+}
+
+/// Debug: MOZ_DBG for AnimationValue.
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_Dump(value: &AnimationValue, result: &mut nsACString) {
+    write!(result, "{:?}", value).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_GetColor(
+    value: &AnimationValue,
+    foreground_color: structs::nscolor,
+) -> structs::nscolor {
+    use style::gecko::values::{
+        convert_absolute_color_to_nscolor, convert_nscolor_to_absolute_color,
+    };
+    use style::values::computed::color::Color as ComputedColor;
+    match *value {
+        AnimationValue::BackgroundColor(ref color) => {
+            let computed: ComputedColor = color.clone();
+            let foreground_color = convert_nscolor_to_absolute_color(foreground_color);
+            convert_absolute_color_to_nscolor(&computed.resolve_to_absolute(&foreground_color))
+        },
+        _ => panic!("Other color properties are not supported yet"),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_IsCurrentColor(value: &AnimationValue) -> bool {
+    match *value {
+        AnimationValue::BackgroundColor(ref color) => color.is_currentcolor(),
+        _ => {
+            debug_assert!(false, "Other color properties are not supported yet");
+            false
+        },
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_GetOpacity(value: &AnimationValue) -> f32 {
+    if let AnimationValue::Opacity(opacity) = *value {
+        opacity
+    } else {
+        panic!("The AnimationValue should be Opacity");
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_Opacity(opacity: f32) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::Opacity(opacity)).into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_Color(
+    color_property: nsCSSPropertyID,
+    color: structs::nscolor,
+) -> Strong<AnimationValue> {
+    use style::gecko::values::convert_nscolor_to_absolute_color;
+    use style::values::animated::color::Color;
+
+    let property = LonghandId::from_nscsspropertyid(color_property)
+        .expect("We don't have shorthand property animation value");
+
+    let animated = convert_nscolor_to_absolute_color(color);
+
+    match property {
+        LonghandId::BackgroundColor => {
+            Arc::new(AnimationValue::BackgroundColor(Color::Absolute(animated))).into()
+        },
+        _ => panic!("Should be background-color property"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetScale(
+    value: &AnimationValue,
+) -> *const computed::Scale {
+    match *value {
+        AnimationValue::Scale(ref value) => value,
+        _ => unreachable!("Expected scale"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetTranslate(
+    value: &AnimationValue,
+) -> *const computed::Translate {
+    match *value {
+        AnimationValue::Translate(ref value) => value,
+        _ => unreachable!("Expected translate"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetRotate(
+    value: &AnimationValue,
+) -> *const computed::Rotate {
+    match *value {
+        AnimationValue::Rotate(ref value) => value,
+        _ => unreachable!("Expected rotate"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetTransform(
+    value: &AnimationValue,
+) -> *const computed::Transform {
+    match *value {
+        AnimationValue::Transform(ref value) => value,
+        _ => unreachable!("Unsupported transform animation value"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetOffsetPath(
+    value: &AnimationValue,
+    output: &mut computed::motion::OffsetPath,
+) {
+    use style::values::animated::ToAnimatedValue;
+    match *value {
+        AnimationValue::OffsetPath(ref value) => {
+            *output = ToAnimatedValue::from_animated_value(value.clone())
+        },
+        _ => unreachable!("Expected offset-path"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetOffsetDistance(
+    value: &AnimationValue,
+) -> *const computed::LengthPercentage {
+    match *value {
+        AnimationValue::OffsetDistance(ref value) => value,
+        _ => unreachable!("Expected offset-distance"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetOffsetRotate(
+    value: &AnimationValue,
+) -> *const computed::motion::OffsetRotate {
+    match *value {
+        AnimationValue::OffsetRotate(ref value) => value,
+        _ => unreachable!("Expected offset-rotate"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetOffsetAnchor(
+    value: &AnimationValue,
+) -> *const computed::position::PositionOrAuto {
+    match *value {
+        AnimationValue::OffsetAnchor(ref value) => value,
+        _ => unreachable!("Expected offset-anchor"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_GetOffsetPosition(
+    value: &AnimationValue,
+) -> *const computed::motion::OffsetPosition {
+    match *value {
+        AnimationValue::OffsetPosition(ref value) => value,
+        _ => unreachable!("Expected offset-position"),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_IsOffsetPathUrl(value: &AnimationValue) -> bool {
+    use style::values::generics::motion::{GenericOffsetPath, GenericOffsetPathFunction};
+    if let AnimationValue::OffsetPath(ref op) = value {
+        if let GenericOffsetPath::OffsetPath { path, coord_box: _ } = op {
+            return matches!(**path, GenericOffsetPathFunction::Url(_));
+        }
+    }
+    false
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_Rotate(
+    r: &computed::Rotate,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::Rotate(r.clone())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_Translate(
+    t: &computed::Translate,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::Translate(t.clone())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_Scale(s: &computed::Scale) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::Scale(s.clone())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_Transform(
+    transform: &computed::Transform,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::Transform(transform.clone())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_OffsetPath(
+    p: &computed::motion::OffsetPath,
+) -> Strong<AnimationValue> {
+    use style::values::animated::ToAnimatedValue;
+    Arc::new(AnimationValue::OffsetPath(p.clone().to_animated_value())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_OffsetDistance(
+    d: &computed::LengthPercentage,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::OffsetDistance(d.clone())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_OffsetRotate(
+    r: &computed::motion::OffsetRotate,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::OffsetRotate(*r)).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_OffsetAnchor(
+    p: &computed::position::PositionOrAuto,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::OffsetAnchor(p.clone())).into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValue_OffsetPosition(
+    p: &computed::motion::OffsetPosition,
+) -> Strong<AnimationValue> {
+    Arc::new(AnimationValue::OffsetPosition(p.clone())).into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_DeepEqual(
+    this: &AnimationValue,
+    other: &AnimationValue,
+) -> bool {
+    this == other
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_Uncompute(
+    value: &AnimationValue,
+) -> Strong<LockedDeclarationBlock> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    Arc::new(
+        global_style_data
+            .shared_lock
+            .wrap(PropertyDeclarationBlock::with_one(
+                value.uncompute(),
+                Importance::Normal,
+            )),
+    )
+    .into()
+}
+
+#[inline]
+fn create_byte_buf_from_vec(mut v: Vec<u8>) -> ByteBuf {
+    let w = ByteBuf {
+        mData: v.as_mut_ptr(),
+        mLen: v.len(),
+        mCapacity: v.capacity(),
+    };
+    std::mem::forget(v);
+    w
+}
+
+#[inline]
+fn view_byte_buf(b: &ByteBuf) -> &[u8] {
+    if b.mData.is_null() {
+        debug_assert_eq!(b.mCapacity, 0);
+        return &[];
+    }
+    unsafe { std::slice::from_raw_parts(b.mData, b.mLen) }
+}
+
+macro_rules! impl_basic_serde_funcs {
+    ($ser_name:ident, $de_name:ident, $computed_type:ty) => {
+        #[no_mangle]
+        pub extern "C" fn $ser_name(v: &$computed_type, output: &mut ByteBuf) -> bool {
+            let buf = match serialize(v) {
+                Ok(buf) => buf,
+                Err(..) => return false,
+            };
+
+            *output = create_byte_buf_from_vec(buf);
+            true
+        }
+
+        #[no_mangle]
+        pub unsafe extern "C" fn $de_name(input: &ByteBuf, v: *mut $computed_type) -> bool {
+            let buf = match deserialize(view_byte_buf(input)) {
+                Ok(buf) => buf,
+                Err(..) => return false,
+            };
+
+            std::ptr::write(v, buf);
+            true
+        }
+    };
+}
+
+impl_basic_serde_funcs!(
+    Servo_LengthPercentage_Serialize,
+    Servo_LengthPercentage_Deserialize,
+    computed::LengthPercentage
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleRotate_Serialize,
+    Servo_StyleRotate_Deserialize,
+    computed::transform::Rotate
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleScale_Serialize,
+    Servo_StyleScale_Deserialize,
+    computed::transform::Scale
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleTranslate_Serialize,
+    Servo_StyleTranslate_Deserialize,
+    computed::transform::Translate
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleTransform_Serialize,
+    Servo_StyleTransform_Deserialize,
+    computed::transform::Transform
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleOffsetPath_Serialize,
+    Servo_StyleOffsetPath_Deserialize,
+    computed::motion::OffsetPath
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleOffsetRotate_Serialize,
+    Servo_StyleOffsetRotate_Deserialize,
+    computed::motion::OffsetRotate
+);
+
+impl_basic_serde_funcs!(
+    Servo_StylePositionOrAuto_Serialize,
+    Servo_StylePositionOrAuto_Deserialize,
+    computed::position::PositionOrAuto
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleOffsetPosition_Serialize,
+    Servo_StyleOffsetPosition_Deserialize,
+    computed::motion::OffsetPosition
+);
+
+impl_basic_serde_funcs!(
+    Servo_StyleComputedTimingFunction_Serialize,
+    Servo_StyleComputedTimingFunction_Deserialize,
+    ComputedTimingFunction
+);
+
+// Return the ComputedValues by a base ComputedValues and the rules.
+fn resolve_rules_for_element_with_context<'a>(
+    element: GeckoElement<'a>,
+    mut context: StyleContext<GeckoElement<'a>>,
+    rules: StrongRuleNode,
+    original_computed_values: &ComputedValues,
+) -> Arc<ComputedValues> {
+    use style::style_resolver::{PseudoElementResolution, StyleResolverForElement};
+
+    // This currently ignores visited styles, which seems acceptable, as
+    // existing browsers don't appear to animate visited styles.
+    let inputs = CascadeInputs {
+        rules: Some(rules),
+        visited_rules: None,
+        flags: original_computed_values.flags.for_cascade_inputs(),
+    };
+
+    // Actually `PseudoElementResolution` doesn't matter.
+    let mut resolver = StyleResolverForElement::new(
+        element,
+        &mut context,
+        RuleInclusion::All,
+        PseudoElementResolution::IfApplicable,
+    );
+    resolver
+        .cascade_style_and_visited_with_default_parents(inputs)
+        .0
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValueMap_Create() -> *mut AnimationValueMap {
+    Box::into_raw(Box::default())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AnimationValueMap_Drop(value_map: *mut AnimationValueMap) {
+    let _ = Box::from_raw(value_map);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValueMap_GetValue(
+    value_map: &AnimationValueMap,
+    property_id: &structs::AnimatedPropertyID,
+) -> Strong<AnimationValue> {
+    let property = match OwnedPropertyDeclarationId::from_gecko_animated_property_id(property_id) {
+        Some(property) => property,
+        None => return Strong::null(),
+    };
+    value_map
+        .get(&property)
+        .map_or(Strong::null(), |value| Arc::new(value.clone()).into())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_GetBaseComputedValuesForElement(
+    raw_style_set: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    computed_values: &ComputedValues,
+    snapshots: *const ServoElementSnapshotTable,
+) -> Strong<ComputedValues> {
+    debug_assert!(!snapshots.is_null());
+    let computed_values = unsafe { ArcBorrow::from_ref(computed_values) };
+
+    let rules = match computed_values.rules {
+        None => return computed_values.clone_arc().into(),
+        Some(ref rules) => rules,
+    };
+
+    let doc_data = raw_style_set.borrow();
+    let without_animations_rules = doc_data.stylist.rule_tree().remove_animation_rules(rules);
+    if without_animations_rules == *rules {
+        return computed_values.clone_arc().into();
+    }
+
+    let element = GeckoElement(element);
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let shared = create_shared_context(
+        &global_style_data,
+        &guard,
+        &doc_data.stylist,
+        TraversalFlags::empty(),
+        unsafe { &*snapshots },
+    );
+    let mut tlc = ThreadLocalStyleContext::new();
+    let context = StyleContext {
+        shared: &shared,
+        thread_local: &mut tlc,
+    };
+
+    resolve_rules_for_element_with_context(
+        element,
+        context,
+        without_animations_rules,
+        &computed_values,
+    )
+    .into()
+}
+
+#[repr(C)]
+#[derive(Default)]
+pub struct ShouldTransitionResult {
+    should_animate: bool,
+    old_transition_value_matches: bool,
+}
+
+#[inline]
+fn is_transitionable(prop: PropertyDeclarationId) -> bool {
+    prop.is_animatable() && !prop.is_discrete_animatable()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_ShouldTransition(
+    old: &ComputedValues,
+    new: &ComputedValues,
+    prop: &structs::AnimatedPropertyID,
+    old_transition_value: Option<&AnimationValue>,
+    start: &mut structs::RefPtr<AnimationValue>,
+    end: &mut structs::RefPtr<AnimationValue>,
+) -> ShouldTransitionResult {
+    let Some(prop) = OwnedPropertyDeclarationId::from_gecko_animated_property_id(prop) else {
+        return Default::default();
+    };
+    let prop = prop.as_borrowed();
+    if !is_transitionable(prop) {
+        return Default::default();
+    }
+
+    let Some(new_value) = AnimationValue::from_computed_values(prop, new) else {
+        return Default::default();
+    };
+
+    if let Some(old_transition_value) = old_transition_value {
+        if *old_transition_value == new_value {
+            return ShouldTransitionResult {
+                should_animate: false,
+                old_transition_value_matches: true,
+            };
+        }
+    }
+
+    let Some(old_value) = AnimationValue::from_computed_values(prop, old) else {
+        return Default::default();
+    };
+    if old_value == new_value || !old_value.interpolable_with(&new_value) {
+        return Default::default();
+    }
+
+    start.set_arc(Arc::new(old_value));
+    end.set_arc(Arc::new(new_value));
+
+    ShouldTransitionResult {
+        should_animate: true,
+        old_transition_value_matches: false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_TransitionValueMatches(
+    style: &ComputedValues,
+    prop: &structs::AnimatedPropertyID,
+    transition_value: &AnimationValue,
+) -> bool {
+    let Some(prop) = OwnedPropertyDeclarationId::from_gecko_animated_property_id(prop) else {
+        return false;
+    };
+    let prop = prop.as_borrowed();
+    if !is_transitionable(prop) {
+        return false;
+    }
+    let Some(value) = AnimationValue::from_computed_values(prop, style) else {
+        return false;
+    };
+    value == *transition_value
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_ExtractAnimationValue(
+    computed_values: &ComputedValues,
+    property_id: &structs::AnimatedPropertyID,
+) -> Strong<AnimationValue> {
+    let property = match OwnedPropertyDeclarationId::from_gecko_animated_property_id(property_id) {
+        Some(property) => property,
+        None => return Strong::null(),
+    };
+    match AnimationValue::from_computed_values(property.as_borrowed(), &computed_values) {
+        Some(v) => Arc::new(v).into(),
+        None => Strong::null(),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ResolveLogicalProperty(
+    property_id: nsCSSPropertyID,
+    style: &ComputedValues,
+) -> nsCSSPropertyID {
+    let longhand = LonghandId::from_nscsspropertyid(property_id)
+        .expect("We shouldn't need to care about shorthands");
+
+    longhand
+        .to_physical(style.writing_mode)
+        .to_nscsspropertyid()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_LookupEnabledForAllContent(
+    prop: &nsACString,
+) -> nsCSSPropertyID {
+    match PropertyId::parse_enabled_for_all_content(prop.as_str_unchecked()) {
+        Ok(p) => p.to_nscsspropertyid_resolving_aliases(),
+        Err(..) => nsCSSPropertyID::eCSSProperty_UNKNOWN,
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_GetName(
+    prop: nsCSSPropertyID,
+    out_length: *mut u32,
+) -> *const u8 {
+    let (ptr, len) = match NonCustomPropertyId::from_nscsspropertyid(prop) {
+        Some(p) => {
+            let name = p.name();
+            (name.as_bytes().as_ptr(), name.len())
+        },
+        None => (ptr::null(), 0),
+    };
+
+    *out_length = len as u32;
+    ptr
+}
+
+macro_rules! parse_enabled_property_name {
+    ($prop_name:ident, $found:ident, $default:expr) => {{
+        let prop_name = $prop_name.as_str_unchecked();
+        match PropertyId::parse_enabled_for_all_content(prop_name) {
+            Ok(p) => {
+                *$found = true;
+                p
+            },
+            Err(..) => {
+                *$found = false;
+                return $default;
+            },
+        }
+    }};
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_IsShorthand(
+    prop_name: &nsACString,
+    found: *mut bool,
+) -> bool {
+    let prop_id = parse_enabled_property_name!(prop_name, found, false);
+    prop_id.is_shorthand()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_IsInherited(
+    per_doc_data: &PerDocumentStyleData,
+    prop_name: &nsACString,
+) -> bool {
+    let prop_name = prop_name.as_str_unchecked();
+    let prop_id = match PropertyId::parse_enabled_for_all_content(prop_name) {
+        Ok(id) => id,
+        Err(_) => return false,
+    };
+    let longhand_id = match prop_id {
+        PropertyId::Custom(property_name) => {
+            let stylist = &per_doc_data.borrow().stylist;
+            return stylist.get_custom_property_registration(&property_name).inherits()
+        },
+        PropertyId::NonCustom(id) => match id.longhand_or_shorthand() {
+            Ok(lh) => lh,
+            Err(sh) => sh.longhands().next().unwrap(),
+        },
+    };
+    longhand_id.inherited()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_SupportsType(
+    prop_name: &nsACString,
+    ty: u8,
+    found: *mut bool,
+) -> bool {
+    let prop_id = parse_enabled_property_name!(prop_name, found, false);
+    prop_id.supports_type(ty)
+}
+
+// TODO(emilio): We could use ThinVec instead of nsTArray.
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_GetCSSValuesForProperty(
+    prop_name: &nsACString,
+    found: *mut bool,
+    result: &mut nsTArray<nsString>,
+) {
+    let prop_id = parse_enabled_property_name!(prop_name, found, ());
+    // Use B-tree set for unique and sorted result.
+    let mut values = BTreeSet::<&'static str>::new();
+    prop_id.collect_property_completion_keywords(&mut |list| values.extend(list.iter()));
+
+    let mut extras = vec![];
+    if values.contains("transparent") {
+        // This is a special value devtools use to avoid inserting the
+        // long list of color keywords. We need to prepend it to values.
+        extras.push("COLOR");
+    }
+
+    let len = extras.len() + values.len();
+    bindings::Gecko_ResizeTArrayForStrings(result, len as u32);
+
+    for (src, dest) in extras.iter().chain(values.iter()).zip(result.iter_mut()) {
+        dest.write_str(src).unwrap();
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Property_IsAnimatable(prop: &structs::AnimatedPropertyID) -> bool {
+    PropertyId::from_gecko_animated_property_id(prop).map_or(false, |p| p.is_animatable())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Property_IsDiscreteAnimatable(property: nsCSSPropertyID) -> bool {
+    match LonghandId::from_nscsspropertyid(property) {
+        Some(longhand) => longhand.is_discrete_animatable(),
+        None => return false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_ClearData(element: &RawGeckoElement) {
+    unsafe { GeckoElement(element).clear_data() };
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_SizeOfExcludingThisAndCVs(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    seen_ptrs: *mut SeenPtrs,
+    element: &RawGeckoElement,
+) -> usize {
+    let element = GeckoElement(element);
+    let borrow = element.borrow_data();
+    if let Some(data) = borrow {
+        let have_seen_ptr = move |ptr| unsafe { Gecko_HaveSeenPtr(seen_ptrs, ptr) };
+        let mut ops = MallocSizeOfOps::new(
+            malloc_size_of.unwrap(),
+            Some(malloc_enclosing_size_of.unwrap()),
+            Some(Box::new(have_seen_ptr)),
+        );
+        (*data).size_of_excluding_cvs(&mut ops)
+    } else {
+        0
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_GetMaybeOutOfDateStyle(
+    element: &RawGeckoElement,
+) -> *const ComputedValues {
+    let element = GeckoElement(element);
+    let data = match element.borrow_data() {
+        Some(d) => d,
+        None => return ptr::null(),
+    };
+    &**data.styles.primary() as *const _
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_GetMaybeOutOfDatePseudoStyle(
+    element: &RawGeckoElement,
+    index: usize,
+) -> *const ComputedValues {
+    let element = GeckoElement(element);
+    let data = match element.borrow_data() {
+        Some(d) => d,
+        None => return ptr::null(),
+    };
+    match data.styles.pseudos.as_array()[index].as_ref() {
+        Some(style) => &**style as *const _,
+        None => ptr::null(),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_IsDisplayNone(element: &RawGeckoElement) -> bool {
+    let element = GeckoElement(element);
+    let data = element
+        .get_data()
+        .expect("Invoking Servo_Element_IsDisplayNone on unstyled element");
+
+    // This function is hot, so we bypass the AtomicRefCell.
+    //
+    // It would be nice to also assert that we're not in the servo traversal,
+    // but this function is called at various intermediate checkpoints when
+    // managing the traversal on the Gecko side.
+    debug_assert!(is_main_thread());
+    unsafe { &*data.as_ptr() }.styles.is_display_none()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_IsDisplayContents(element: &RawGeckoElement) -> bool {
+    let element = GeckoElement(element);
+    let data = element
+        .get_data()
+        .expect("Invoking Servo_Element_IsDisplayContents on unstyled element");
+
+    debug_assert!(is_main_thread());
+    unsafe { &*data.as_ptr() }
+        .styles
+        .primary()
+        .get_box()
+        .clone_display()
+        .is_contents()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Element_IsPrimaryStyleReusedViaRuleNode(element: &RawGeckoElement) -> bool {
+    let element = GeckoElement(element);
+    let data = element
+        .borrow_data()
+        .expect("Invoking Servo_Element_IsPrimaryStyleReusedViaRuleNode on unstyled element");
+    data.flags
+        .contains(data::ElementDataFlags::PRIMARY_STYLE_REUSED_VIA_RULE_NODE)
+}
+
+fn mode_to_origin(mode: SheetParsingMode) -> Origin {
+    match mode {
+        SheetParsingMode::eAuthorSheetFeatures => Origin::Author,
+        SheetParsingMode::eUserSheetFeatures => Origin::User,
+        SheetParsingMode::eAgentSheetFeatures => Origin::UserAgent,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_Empty(mode: SheetParsingMode) -> Strong<StylesheetContents> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let origin = mode_to_origin(mode);
+    let shared_lock = &global_style_data.shared_lock;
+    StylesheetContents::from_str(
+        "",
+        unsafe { dummy_url_data() }.clone(),
+        origin,
+        shared_lock,
+        /* loader = */ None,
+        None,
+        QuirksMode::NoQuirks,
+        /* use_counters = */ None,
+        AllowImportRules::Yes,
+        /* sanitization_data = */ None,
+    )
+    .into()
+}
+
+/// Note: The load_data corresponds to this sheet, and is passed as the parent
+/// load data for child sheet loads. It may be null for certain cases where we
+/// know we won't have child loads.
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSheet_FromUTF8Bytes(
+    loader: *mut Loader,
+    stylesheet: *mut DomStyleSheet,
+    load_data: *mut SheetLoadData,
+    bytes: &nsACString,
+    mode: SheetParsingMode,
+    extra_data: *mut URLExtraData,
+    quirks_mode: nsCompatibility,
+    reusable_sheets: *mut LoaderReusableStyleSheets,
+    use_counters: Option<&UseCounters>,
+    allow_import_rules: AllowImportRules,
+    sanitization_kind: SanitizationKind,
+    sanitized_output: Option<&mut nsAString>,
+) -> Strong<StylesheetContents> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let input = bytes.as_str_unchecked();
+
+    let reporter = ErrorReporter::new(stylesheet, loader, extra_data);
+    let url_data = UrlExtraData::from_ptr_ref(&extra_data);
+    let loader = if loader.is_null() {
+        None
+    } else {
+        debug_assert!(
+            sanitized_output.is_none(),
+            "Shouldn't trigger @import loads for sanitization",
+        );
+        Some(StylesheetLoader::new(
+            loader,
+            stylesheet,
+            load_data,
+            reusable_sheets,
+        ))
+    };
+
+    // FIXME(emilio): loader.as_ref() doesn't typecheck for some reason?
+    let loader: Option<&dyn StyleStylesheetLoader> = match loader {
+        None => None,
+        Some(ref s) => Some(s),
+    };
+
+    let mut sanitization_data = SanitizationData::new(sanitization_kind);
+
+    let contents = StylesheetContents::from_str(
+        input,
+        url_data.clone(),
+        mode_to_origin(mode),
+        &global_style_data.shared_lock,
+        loader,
+        reporter.as_ref().map(|r| r as &dyn ParseErrorReporter),
+        quirks_mode.into(),
+        use_counters,
+        allow_import_rules,
+        sanitization_data.as_mut(),
+    );
+
+    if let Some(data) = sanitization_data {
+        sanitized_output
+            .unwrap()
+            .assign_utf8(data.take().as_bytes());
+    }
+
+    contents.into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSheet_FromUTF8BytesAsync(
+    load_data: *mut SheetLoadDataHolder,
+    extra_data: *mut URLExtraData,
+    bytes: &nsACString,
+    mode: SheetParsingMode,
+    quirks_mode: nsCompatibility,
+    should_record_use_counters: bool,
+    allow_import_rules: AllowImportRules,
+) {
+    let load_data = RefPtr::new(load_data);
+    let extra_data = UrlExtraData::new(extra_data);
+
+    let mut sheet_bytes = nsCString::new();
+    sheet_bytes.assign(bytes);
+
+    let async_parser = AsyncStylesheetParser::new(
+        load_data,
+        extra_data,
+        sheet_bytes,
+        mode_to_origin(mode),
+        quirks_mode.into(),
+        should_record_use_counters,
+        allow_import_rules,
+    );
+
+    if let Some(thread_pool) = STYLE_THREAD_POOL.pool().as_ref() {
+        thread_pool.spawn(|| {
+            gecko_profiler_label!(Layout, CSSParsing);
+            async_parser.parse();
+        });
+    } else {
+        async_parser.parse();
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ShutdownThreadPool() {
+    debug_assert!(is_main_thread() && !is_in_servo_traversal());
+    StyleThreadPool::shutdown();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ThreadPool_GetThreadHandles(
+    handles: &mut ThinVec<PlatformThreadHandle>,
+) {
+    StyleThreadPool::get_thread_handles(handles);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSheet_FromSharedData(
+    extra_data: *mut URLExtraData,
+    shared_rules: &LockedCssRules,
+) -> Strong<StylesheetContents> {
+    StylesheetContents::from_shared_data(
+        Arc::from_raw_addrefed(shared_rules),
+        Origin::UserAgent,
+        UrlExtraData::new(extra_data),
+        QuirksMode::NoQuirks,
+    )
+    .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_AppendStyleSheet(
+    raw_data: &PerDocumentStyleData,
+    sheet: *const DomStyleSheet,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut data = raw_data.borrow_mut();
+    let data = &mut *data;
+    let guard = global_style_data.shared_lock.read();
+    let sheet = unsafe { GeckoStyleSheet::new(sheet) };
+    data.stylist.append_stylesheet(sheet, &guard);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AuthorStyles_Create() -> *mut AuthorStyles {
+    Box::into_raw(Box::new(AuthorStyles::new()))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AuthorStyles_Drop(styles: *mut AuthorStyles) {
+    let _ = Box::from_raw(styles);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AuthorStyles_AppendStyleSheet(
+    styles: &mut AuthorStyles,
+    sheet: *const DomStyleSheet,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let sheet = GeckoStyleSheet::new(sheet);
+    styles.stylesheets.append_stylesheet(None, sheet, &guard);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AuthorStyles_InsertStyleSheetBefore(
+    styles: &mut AuthorStyles,
+    sheet: *const DomStyleSheet,
+    before_sheet: *const DomStyleSheet,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    styles.stylesheets.insert_stylesheet_before(
+        None,
+        GeckoStyleSheet::new(sheet),
+        GeckoStyleSheet::new(before_sheet),
+        &guard,
+    );
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AuthorStyles_RemoveStyleSheet(
+    styles: &mut AuthorStyles,
+    sheet: *const DomStyleSheet,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    styles
+        .stylesheets
+        .remove_stylesheet(None, GeckoStyleSheet::new(sheet), &guard);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AuthorStyles_ForceDirty(styles: &mut AuthorStyles) {
+    styles.stylesheets.force_dirty();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AuthorStyles_IsDirty(styles: &AuthorStyles) -> bool {
+    styles.stylesheets.dirty()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AuthorStyles_Flush(
+    styles: &mut AuthorStyles,
+    document_set: &PerDocumentStyleData,
+) {
+    // Try to avoid the atomic borrow below if possible.
+    if !styles.stylesheets.dirty() {
+        return;
+    }
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    let mut document_data = document_set.borrow_mut();
+
+    // TODO(emilio): This is going to need an element or something to do proper
+    // invalidation in Shadow roots.
+    styles.flush::<GeckoElement>(&mut document_data.stylist, &guard);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_RemoveUniqueEntriesFromAuthorStylesCache(
+    document_set: &PerDocumentStyleData,
+) {
+    let mut document_data = document_set.borrow_mut();
+    document_data
+        .stylist
+        .remove_unique_author_data_cache_entries();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SizeOfIncludingThis(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    declarations: &LockedDeclarationBlock,
+) -> usize {
+    use malloc_size_of::MallocSizeOf;
+    use malloc_size_of::MallocUnconditionalShallowSizeOf;
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    let mut ops = MallocSizeOfOps::new(
+        malloc_size_of.unwrap(),
+        Some(malloc_enclosing_size_of.unwrap()),
+        None,
+    );
+
+    ArcBorrow::from_ref(declarations).with_arc(|declarations| {
+        let mut n = 0;
+        n += declarations.unconditional_shallow_size_of(&mut ops);
+        n += declarations.read_with(&guard).size_of(&mut ops);
+        n
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_AuthorStyles_SizeOfIncludingThis(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    styles: &AuthorStyles,
+) -> usize {
+    // We cannot `use` MallocSizeOf at the top level, otherwise the compiler
+    // would complain in `Servo_StyleSheet_SizeOfIncludingThis` for `size_of`
+    // there.
+    use malloc_size_of::MallocSizeOf;
+    let malloc_size_of = malloc_size_of.unwrap();
+    let malloc_size_of_this = malloc_size_of(styles as *const AuthorStyles as *const c_void);
+
+    let mut ops = MallocSizeOfOps::new(
+        malloc_size_of,
+        Some(malloc_enclosing_size_of.unwrap()),
+        None,
+    );
+    malloc_size_of_this + styles.size_of(&mut ops)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_MediumFeaturesChanged(
+    document_set: &PerDocumentStyleData,
+    non_document_styles: &mut nsTArray<&mut AuthorStyles>,
+    may_affect_default_style: bool,
+) -> structs::MediumFeaturesChangedResult {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    // NOTE(emilio): We don't actually need to flush the stylist here and ensure
+    // it's up to date.
+    //
+    // In case it isn't we would trigger a rebuild + restyle as needed too.
+    //
+    // We need to ensure the default computed values are up to date though,
+    // because those can influence the result of media query evaluation.
+    let mut document_data = document_set.borrow_mut();
+
+    if may_affect_default_style {
+        document_data.stylist.device_mut().reset_computed_values();
+    }
+    let guards = StylesheetGuards::same(&guard);
+
+    let origins_in_which_rules_changed = document_data
+        .stylist
+        .media_features_change_changed_style(&guards, document_data.stylist.device());
+
+    let affects_document_rules = !origins_in_which_rules_changed.is_empty();
+    if affects_document_rules {
+        document_data
+            .stylist
+            .force_stylesheet_origins_dirty(origins_in_which_rules_changed);
+    }
+
+    let mut affects_non_document_rules = false;
+    for author_styles in &mut **non_document_styles {
+        let affected_style = author_styles.stylesheets.iter().any(|sheet| {
+            !author_styles.data.media_feature_affected_matches(
+                sheet,
+                &guards.author,
+                document_data.stylist.device(),
+                document_data.stylist.quirks_mode(),
+            )
+        });
+        if affected_style {
+            affects_non_document_rules = true;
+            author_styles.stylesheets.force_dirty();
+        }
+    }
+
+    structs::MediumFeaturesChangedResult {
+        mAffectsDocumentRules: affects_document_rules,
+        mAffectsNonDocumentRules: affects_non_document_rules,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_InsertStyleSheetBefore(
+    raw_data: &PerDocumentStyleData,
+    sheet: *const DomStyleSheet,
+    before_sheet: *const DomStyleSheet,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut data = raw_data.borrow_mut();
+    let data = &mut *data;
+    let guard = global_style_data.shared_lock.read();
+    let sheet = unsafe { GeckoStyleSheet::new(sheet) };
+    data.stylist.insert_stylesheet_before(
+        sheet,
+        unsafe { GeckoStyleSheet::new(before_sheet) },
+        &guard,
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_RemoveStyleSheet(
+    raw_data: &PerDocumentStyleData,
+    sheet: *const DomStyleSheet,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut data = raw_data.borrow_mut();
+    let data = &mut *data;
+    let guard = global_style_data.shared_lock.read();
+    let sheet = unsafe { GeckoStyleSheet::new(sheet) };
+    data.stylist.remove_stylesheet(sheet, &guard);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_GetSheetAt(
+    raw_data: &PerDocumentStyleData,
+    origin: Origin,
+    index: usize,
+) -> *const DomStyleSheet {
+    let data = raw_data.borrow();
+    data.stylist
+        .sheet_at(origin, index)
+        .map_or(ptr::null(), |s| s.raw())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_GetSheetCount(
+    raw_data: &PerDocumentStyleData,
+    origin: Origin,
+) -> usize {
+    let data = raw_data.borrow();
+    data.stylist.sheet_count(origin)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_FlushStyleSheets(
+    raw_data: &PerDocumentStyleData,
+    doc_element: Option<&RawGeckoElement>,
+    snapshots: *const ServoElementSnapshotTable,
+) {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let mut data = raw_data.borrow_mut();
+    let doc_element = doc_element.map(GeckoElement);
+
+    let have_invalidations = data.flush_stylesheets(&guard, doc_element, snapshots.as_ref());
+
+    if have_invalidations && doc_element.is_some() {
+        // The invalidation machinery propagates the bits up, but we still need
+        // to tell the Gecko restyle root machinery about it.
+        bindings::Gecko_NoteDirtySubtreeForInvalidation(doc_element.unwrap().0);
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_NoteStyleSheetsChanged(
+    raw_data: &PerDocumentStyleData,
+    changed_origins: OriginFlags,
+) {
+    let mut data = raw_data.borrow_mut();
+    data.stylist
+        .force_stylesheet_origins_dirty(OriginSet::from(changed_origins));
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_SetAuthorStyleDisabled(
+    raw_data: &PerDocumentStyleData,
+    author_style_disabled: bool,
+) {
+    let mut data = raw_data.borrow_mut();
+    let enabled = if author_style_disabled {
+        AuthorStylesEnabled::No
+    } else {
+        AuthorStylesEnabled::Yes
+    };
+    data.stylist.set_author_styles_enabled(enabled);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_UsesFontMetrics(raw_data: &PerDocumentStyleData) -> bool {
+    let doc_data = raw_data;
+    doc_data.borrow().stylist.device().used_font_metrics()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_HasRules(raw_contents: &StylesheetContents) -> bool {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    !raw_contents.rules.read_with(&guard).0.is_empty()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_GetRules(sheet: &StylesheetContents) -> Strong<LockedCssRules> {
+    sheet.rules.clone().into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_Clone(
+    contents: &StylesheetContents,
+    reference_sheet: *const DomStyleSheet,
+) -> Strong<StylesheetContents> {
+    use style::shared_lock::{DeepCloneParams, DeepCloneWithLock};
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let params = DeepCloneParams { reference_sheet };
+
+    Arc::new(contents.deep_clone_with_lock(&global_style_data.shared_lock, &guard, &params)).into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_SizeOfIncludingThis(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    sheet: &StylesheetContents,
+) -> usize {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let mut ops = MallocSizeOfOps::new(
+        malloc_size_of.unwrap(),
+        Some(malloc_enclosing_size_of.unwrap()),
+        None,
+    );
+    // TODO(emilio): We're not measuring the size of the Arc<StylesheetContents>
+    // allocation itself here.
+    sheet.size_of(&guard, &mut ops)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_GetOrigin(sheet: &StylesheetContents) -> Origin {
+    sheet.origin
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_GetSourceMapURL(
+    contents: &StylesheetContents,
+    result: &mut nsACString,
+) {
+    let url_opt = contents.source_map_url.read();
+    if let Some(ref url) = *url_opt {
+        result.assign(url);
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSheet_GetSourceURL(
+    contents: &StylesheetContents,
+    result: &mut nsACString,
+) {
+    let url_opt = contents.source_url.read();
+    if let Some(ref url) = *url_opt {
+        result.assign(url);
+    }
+}
+
+fn with_maybe_worker_shared_lock<R>(func: impl FnOnce(&SharedRwLock) -> R) -> R {
+    if is_dom_worker_thread() {
+        DOM_WORKER_RWLOCK.with(func)
+    } else {
+        func(&GLOBAL_STYLE_DATA.shared_lock)
+    }
+}
+
+fn read_locked_arc<T, R, F>(raw: &Locked<T>, func: F) -> R
+where
+    F: FnOnce(&T) -> R,
+{
+    debug_assert!(!is_dom_worker_thread());
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    func(raw.read_with(&guard))
+}
+
+fn read_locked_arc_worker<T, R, F>(raw: &Locked<T>, func: F) -> R
+where
+    F: FnOnce(&T) -> R,
+{
+    with_maybe_worker_shared_lock(|lock| {
+        let guard = lock.read();
+        func(raw.read_with(&guard))
+    })
+}
+
+#[cfg(debug_assertions)]
+unsafe fn read_locked_arc_unchecked<T, R, F>(raw: &Locked<T>, func: F) -> R
+where
+    F: FnOnce(&T) -> R,
+{
+    debug_assert!(is_main_thread() && !is_in_servo_traversal());
+    read_locked_arc(raw, func)
+}
+
+#[cfg(not(debug_assertions))]
+unsafe fn read_locked_arc_unchecked<T, R, F>(raw: &Locked<T>, func: F) -> R
+where
+    F: FnOnce(&T) -> R,
+{
+    debug_assert!(!is_dom_worker_thread());
+    func(raw.read_unchecked())
+}
+
+fn write_locked_arc<T, R, F>(raw: &Locked<T>, func: F) -> R
+where
+    F: FnOnce(&mut T) -> R,
+{
+    debug_assert!(!is_dom_worker_thread());
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let mut guard = global_style_data.shared_lock.write();
+    func(raw.write_with(&mut guard))
+}
+
+fn write_locked_arc_worker<T, R, F>(raw: &Locked<T>, func: F) -> R
+where
+    F: FnOnce(&mut T) -> R,
+{
+    with_maybe_worker_shared_lock(|lock| {
+        let mut guard = lock.write();
+        func(raw.write_with(&mut guard))
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CssRules_ListTypes(rules: &LockedCssRules, result: &mut nsTArray<usize>) {
+    read_locked_arc(rules, |rules: &CssRules| {
+        result.assign_from_iter_pod(rules.0.iter().map(|rule| rule.rule_type() as usize));
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CssRules_InsertRule(
+    rules: &LockedCssRules,
+    contents: &StylesheetContents,
+    rule: &nsACString,
+    index: u32,
+    containing_rule_types: u32,
+    loader: *mut Loader,
+    allow_import_rules: AllowImportRules,
+    gecko_stylesheet: *mut DomStyleSheet,
+    rule_type: &mut CssRuleType,
+) -> nsresult {
+    let loader = if loader.is_null() {
+        None
+    } else {
+        Some(StylesheetLoader::new(
+            loader,
+            gecko_stylesheet,
+            ptr::null_mut(),
+            ptr::null_mut(),
+        ))
+    };
+    let loader = loader
+        .as_ref()
+        .map(|loader| loader as &dyn StyleStylesheetLoader);
+    let rule = unsafe { rule.as_str_unchecked() };
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let result = rules.insert_rule(
+        &global_style_data.shared_lock,
+        rule,
+        contents,
+        index as usize,
+        CssRuleTypes::from_bits(containing_rule_types),
+        loader,
+        allow_import_rules,
+    );
+
+    match result {
+        Ok(new_rule) => {
+            *rule_type = new_rule.rule_type();
+            nsresult::NS_OK
+        },
+        Err(err) => err.into(),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CssRules_DeleteRule(rules: &LockedCssRules, index: u32) -> nsresult {
+    write_locked_arc(rules, |rules: &mut CssRules| {
+        match rules.remove_rule(index as usize) {
+            Ok(_) => nsresult::NS_OK,
+            Err(err) => err.into(),
+        }
+    })
+}
+
+trait MaybeLocked<Target> {
+    fn maybe_locked_read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a Target;
+}
+
+impl<T> MaybeLocked<T> for T {
+    fn maybe_locked_read<'a>(&'a self, _: &'a SharedRwLockReadGuard) -> &'a T {
+        self
+    }
+}
+
+impl<T> MaybeLocked<T> for Locked<T> {
+    fn maybe_locked_read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a T {
+        self.read_with(guard)
+    }
+}
+
+macro_rules! impl_basic_rule_funcs_without_getter {
+    {
+        ($rule_type:ty, $maybe_locked_rule_type:ty),
+        debug: $debug:ident,
+        to_css: $to_css:ident,
+    } => {
+        #[cfg(debug_assertions)]
+        #[no_mangle]
+        pub extern "C" fn $debug(rule: &$maybe_locked_rule_type, result: &mut nsACString) {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            let rule: &$rule_type = rule.maybe_locked_read(&guard);
+            write!(result, "{:?}", *rule).unwrap();
+        }
+
+        #[cfg(not(debug_assertions))]
+        #[no_mangle]
+        pub extern "C" fn $debug(_: &$maybe_locked_rule_type, _: &mut nsACString) {
+            unreachable!()
+        }
+
+        #[no_mangle]
+        pub extern "C" fn $to_css(rule: &$maybe_locked_rule_type, result: &mut nsACString) {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            let rule: &$rule_type = rule.maybe_locked_read(&guard);
+            rule.to_css(&guard, result).unwrap();
+        }
+    }
+}
+
+macro_rules! impl_basic_rule_funcs {
+    { ($name:ident, $rule_type:ty, $maybe_locked_rule_type:ty),
+        getter: $getter:ident,
+        debug: $debug:ident,
+        to_css: $to_css:ident,
+        changed: $changed:ident,
+    } => {
+        #[no_mangle]
+        pub extern "C" fn $getter(
+            rules: &LockedCssRules,
+            index: u32,
+            line: &mut u32,
+            column: &mut u32,
+        ) -> Strong<$maybe_locked_rule_type> {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            let rules = rules.read_with(&guard);
+            let index = index as usize;
+
+            if index >= rules.0.len() {
+                return Strong::null();
+            }
+
+            match rules.0[index] {
+                CssRule::$name(ref arc) => {
+                    let rule: &$rule_type = (&**arc).maybe_locked_read(&guard);
+                    let location = rule.source_location;
+                    *line = location.line as u32;
+                    *column = location.column as u32;
+                    arc.clone().into()
+                },
+                _ => {
+                    Strong::null()
+                }
+            }
+        }
+
+        #[no_mangle]
+        pub extern "C" fn $changed(
+            styleset: &PerDocumentStyleData,
+            rule: &$maybe_locked_rule_type,
+            sheet: &DomStyleSheet,
+            change_kind: RuleChangeKind,
+        ) {
+            let mut data = styleset.borrow_mut();
+            let data = &mut *data;
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            // TODO(emilio): Would be nice not to deal with refcount bumps here,
+            // but it's probably not a huge deal.
+            let rule = unsafe { CssRule::$name(Arc::from_raw_addrefed(rule)) };
+            let sheet = unsafe { GeckoStyleSheet::new(sheet) };
+            data.stylist.rule_changed(&sheet, &rule, &guard, change_kind);
+        }
+
+        impl_basic_rule_funcs_without_getter! {
+            ($rule_type, $maybe_locked_rule_type),
+            debug: $debug,
+            to_css: $to_css,
+        }
+    }
+}
+
+macro_rules! impl_group_rule_funcs {
+    { ($name:ident, $rule_type:ty, $maybe_locked_rule_type:ty),
+      get_rules: $get_rules:ident,
+      $($basic:tt)+
+    } => {
+        impl_basic_rule_funcs! { ($name, $rule_type, $maybe_locked_rule_type), $($basic)+ }
+
+        #[no_mangle]
+        pub extern "C" fn $get_rules(rule: &$maybe_locked_rule_type) -> Strong<LockedCssRules> {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let guard = global_style_data.shared_lock.read();
+            let rule: &$rule_type = rule.maybe_locked_read(&guard);
+            rule.rules.clone().into()
+        }
+    }
+}
+
+impl_basic_rule_funcs! { (Style, StyleRule, Locked<StyleRule>),
+    getter: Servo_CssRules_GetStyleRuleAt,
+    debug: Servo_StyleRule_Debug,
+    to_css: Servo_StyleRule_GetCssText,
+    changed: Servo_StyleSet_StyleRuleChanged,
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_EnsureRules(
+    rule: &LockedStyleRule,
+    read_only: bool,
+) -> Strong<LockedCssRules> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let lock = &global_style_data.shared_lock;
+    if read_only {
+        let guard = lock.read();
+        if let Some(ref rules) = rule.read_with(&guard).rules {
+            return rules.clone().into();
+        }
+        return CssRules::new(vec![], lock).into();
+    }
+    let mut guard = lock.write();
+    rule.write_with(&mut guard)
+        .rules
+        .get_or_insert_with(|| CssRules::new(vec![], lock))
+        .clone()
+        .into()
+}
+
+impl_basic_rule_funcs! { (Import, ImportRule, Locked<ImportRule>),
+    getter: Servo_CssRules_GetImportRuleAt,
+    debug: Servo_ImportRule_Debug,
+    to_css: Servo_ImportRule_GetCssText,
+    changed: Servo_StyleSet_ImportRuleChanged,
+}
+
+impl_basic_rule_funcs_without_getter! { (Keyframe, Locked<Keyframe>),
+    debug: Servo_Keyframe_Debug,
+    to_css: Servo_Keyframe_GetCssText,
+}
+
+impl_basic_rule_funcs! { (Keyframes, KeyframesRule, Locked<KeyframesRule>),
+    getter: Servo_CssRules_GetKeyframesRuleAt,
+    debug: Servo_KeyframesRule_Debug,
+    to_css: Servo_KeyframesRule_GetCssText,
+    changed: Servo_StyleSet_KeyframesRuleChanged,
+}
+
+impl_group_rule_funcs! { (Media, MediaRule, MediaRule),
+    get_rules: Servo_MediaRule_GetRules,
+    getter: Servo_CssRules_GetMediaRuleAt,
+    debug: Servo_MediaRule_Debug,
+    to_css: Servo_MediaRule_GetCssText,
+    changed: Servo_StyleSet_MediaRuleChanged,
+}
+
+impl_basic_rule_funcs! { (Namespace, NamespaceRule, NamespaceRule),
+    getter: Servo_CssRules_GetNamespaceRuleAt,
+    debug: Servo_NamespaceRule_Debug,
+    to_css: Servo_NamespaceRule_GetCssText,
+    changed: Servo_StyleSet_NamespaceRuleChanged,
+}
+
+impl_basic_rule_funcs! { (Page, PageRule, Locked<PageRule>),
+    getter: Servo_CssRules_GetPageRuleAt,
+    debug: Servo_PageRule_Debug,
+    to_css: Servo_PageRule_GetCssText,
+    changed: Servo_StyleSet_PageRuleChanged,
+}
+
+impl_basic_rule_funcs! { (Property, PropertyRule, PropertyRule),
+    getter: Servo_CssRules_GetPropertyRuleAt,
+    debug: Servo_PropertyRule_Debug,
+    to_css: Servo_PropertyRule_GetCssText,
+    changed: Servo_StyleSet_PropertyRuleChanged,
+}
+
+impl_group_rule_funcs! { (Supports, SupportsRule, SupportsRule),
+    get_rules: Servo_SupportsRule_GetRules,
+    getter: Servo_CssRules_GetSupportsRuleAt,
+    debug: Servo_SupportsRule_Debug,
+    to_css: Servo_SupportsRule_GetCssText,
+    changed: Servo_StyleSet_SupportsRuleChanged,
+}
+
+impl_group_rule_funcs! { (Container, ContainerRule, ContainerRule),
+    get_rules: Servo_ContainerRule_GetRules,
+    getter: Servo_CssRules_GetContainerRuleAt,
+    debug: Servo_ContainerRule_Debug,
+    to_css: Servo_ContainerRule_GetCssText,
+    changed: Servo_StyleSet_ContainerRuleChanged,
+}
+
+impl_group_rule_funcs! { (LayerBlock, LayerBlockRule, LayerBlockRule),
+    get_rules: Servo_LayerBlockRule_GetRules,
+    getter: Servo_CssRules_GetLayerBlockRuleAt,
+    debug: Servo_LayerBlockRule_Debug,
+    to_css: Servo_LayerBlockRule_GetCssText,
+    changed: Servo_StyleSet_LayerBlockRuleChanged,
+}
+
+impl_basic_rule_funcs! { (LayerStatement, LayerStatementRule, LayerStatementRule),
+    getter: Servo_CssRules_GetLayerStatementRuleAt,
+    debug: Servo_LayerStatementRule_Debug,
+    to_css: Servo_LayerStatementRule_GetCssText,
+    changed: Servo_StyleSet_LayerStatementRuleChanged,
+}
+
+impl_group_rule_funcs! { (Document, DocumentRule, DocumentRule),
+    get_rules: Servo_DocumentRule_GetRules,
+    getter: Servo_CssRules_GetDocumentRuleAt,
+    debug: Servo_DocumentRule_Debug,
+    to_css: Servo_DocumentRule_GetCssText,
+    changed: Servo_StyleSet_DocumentRuleChanged,
+}
+
+impl_basic_rule_funcs! { (FontFeatureValues, FontFeatureValuesRule, FontFeatureValuesRule),
+    getter: Servo_CssRules_GetFontFeatureValuesRuleAt,
+    debug: Servo_FontFeatureValuesRule_Debug,
+    to_css: Servo_FontFeatureValuesRule_GetCssText,
+    changed: Servo_StyleSet_FontFeatureValuesRuleChanged,
+}
+
+impl_basic_rule_funcs! { (FontPaletteValues, FontPaletteValuesRule, FontPaletteValuesRule),
+    getter: Servo_CssRules_GetFontPaletteValuesRuleAt,
+    debug: Servo_FontPaletteValuesRule_Debug,
+    to_css: Servo_FontPaletteValuesRule_GetCssText,
+    changed: Servo_StyleSet_FontPaletteValuesRuleChanged,
+}
+
+impl_basic_rule_funcs! { (FontFace, FontFaceRule, Locked<FontFaceRule>),
+    getter: Servo_CssRules_GetFontFaceRuleAt,
+    debug: Servo_FontFaceRule_Debug,
+    to_css: Servo_FontFaceRule_GetCssText,
+    changed: Servo_StyleSet_FontFaceRuleChanged,
+}
+
+impl_basic_rule_funcs! { (CounterStyle, CounterStyleRule, Locked<CounterStyleRule>),
+    getter: Servo_CssRules_GetCounterStyleRuleAt,
+    debug: Servo_CounterStyleRule_Debug,
+    to_css: Servo_CounterStyleRule_GetCssText,
+    changed: Servo_StyleSet_CounterStyleRuleChanged,
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_GetStyle(
+    rule: &LockedStyleRule,
+) -> Strong<LockedDeclarationBlock> {
+    read_locked_arc(rule, |rule: &StyleRule| rule.block.clone().into())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_SetStyle(
+    rule: &LockedStyleRule,
+    declarations: &LockedDeclarationBlock,
+) {
+    write_locked_arc(rule, |rule: &mut StyleRule| {
+        rule.block = unsafe { Arc::from_raw_addrefed(declarations) };
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_GetSelectorText(rule: &LockedStyleRule, result: &mut nsACString) {
+    read_locked_arc(rule, |rule| rule.selectors.to_css(result).unwrap());
+}
+
+fn desugared_selector_list(rules: &ThinVec<&LockedStyleRule>) -> SelectorList {
+    let mut selectors: Option<SelectorList> = None;
+    for rule in rules.iter().rev() {
+        selectors = Some(read_locked_arc(rule, |rule| match selectors {
+            Some(ref s) => rule.selectors.replace_parent_selector(s),
+            None => rule.selectors.clone(),
+        }));
+    }
+    selectors.expect("Empty rule chain?")
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_GetSelectorDataAtIndex(
+    rules: &ThinVec<&LockedStyleRule>,
+    index: u32,
+    text: Option<&mut nsACString>,
+    specificity: Option<&mut u64>,
+) {
+    let selectors = desugared_selector_list(rules);
+    let Some(selector) = selectors.slice().get(index as usize) else {
+        return;
+    };
+    if let Some(text) = text {
+        selector.to_css(text).unwrap();
+    }
+    if let Some(specificity) = specificity {
+        *specificity = selector.specificity() as u64;
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_GetSelectorCount(rule: &LockedStyleRule) -> u32 {
+    read_locked_arc(rule, |rule| rule.selectors.len() as u32)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_SelectorMatchesElement(
+    rules: &ThinVec<&LockedStyleRule>,
+    element: &RawGeckoElement,
+    index: u32,
+    host: Option<&RawGeckoElement>,
+    pseudo_type: PseudoStyleType,
+    relevant_link_visited: bool,
+) -> bool {
+    use selectors::matching::{
+        matches_selector, MatchingContext, MatchingMode, NeedsSelectorFlags, VisitedHandlingMode,
+    };
+    let selectors = desugared_selector_list(rules);
+    let Some(selector) = selectors.slice().get(index as usize) else {
+        return false;
+    };
+    let mut matching_mode = MatchingMode::Normal;
+    match PseudoElement::from_pseudo_type(pseudo_type, None) {
+        Some(pseudo) => {
+            // We need to make sure that the requested pseudo element type
+            // matches the selector pseudo element type before proceeding.
+            match selector.pseudo_element() {
+                Some(selector_pseudo) if *selector_pseudo == pseudo => {
+                    matching_mode = MatchingMode::ForStatelessPseudoElement
+                },
+                _ => return false,
+            };
+        },
+        None => {
+            // Do not attempt to match if a pseudo element is requested and
+            // this is not a pseudo element selector, or vice versa.
+            if selector.has_pseudo_element() {
+                return false;
+            }
+        },
+    };
+
+    let element = GeckoElement(element);
+    let host = host.map(GeckoElement);
+    let quirks_mode = element.as_node().owner_doc().quirks_mode();
+    let mut selector_caches = SelectorCaches::default();
+    let visited_mode = if relevant_link_visited {
+        VisitedHandlingMode::RelevantLinkVisited
+    } else {
+        VisitedHandlingMode::AllLinksUnvisited
+    };
+    let mut ctx = MatchingContext::new_for_visited(
+        matching_mode,
+        /* bloom_filter = */ None,
+        &mut selector_caches,
+        visited_mode,
+        quirks_mode,
+        NeedsSelectorFlags::No,
+        MatchingForInvalidation::No,
+    );
+    ctx.with_shadow_host(host, |ctx| {
+        matches_selector(selector, 0, None, &element, ctx)
+    })
+}
+
+pub type SelectorList = selectors::SelectorList<style::gecko::selector_parser::SelectorImpl>;
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleRule_SetSelectorText(
+    contents: &StylesheetContents,
+    rule: &LockedStyleRule,
+    text: &nsACString,
+) -> bool {
+    let value_str = unsafe { text.as_str_unchecked() };
+
+    write_locked_arc(rule, |rule: &mut StyleRule| {
+        use selectors::parser::ParseRelative;
+        use style::selector_parser::SelectorParser;
+
+        let namespaces = contents.namespaces.read();
+        let url_data = contents.url_data.read();
+        let parser = SelectorParser {
+            stylesheet_origin: contents.origin,
+            namespaces: &namespaces,
+            url_data: &url_data,
+            for_supports_rule: false,
+        };
+
+        // TODO: Maybe allow setting relative selectors from the OM, if we're in a nested style
+        // rule?
+        let mut parser_input = ParserInput::new(&value_str);
+        match SelectorList::parse(
+            &parser,
+            &mut Parser::new(&mut parser_input),
+            ParseRelative::No,
+        ) {
+            Ok(selectors) => {
+                rule.selectors = selectors;
+                true
+            },
+            Err(_) => false,
+        }
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SelectorList_Closest(
+    element: &RawGeckoElement,
+    selectors: &SelectorList,
+) -> *const RawGeckoElement {
+    use style::dom_apis;
+
+    let element = GeckoElement(element);
+    let quirks_mode = element.as_node().owner_doc().quirks_mode();
+    dom_apis::element_closest(element, &selectors, quirks_mode).map_or(ptr::null(), |e| e.0)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SelectorList_Matches(
+    element: &RawGeckoElement,
+    selectors: &SelectorList,
+) -> bool {
+    use style::dom_apis;
+
+    let element = GeckoElement(element);
+    let quirks_mode = element.as_node().owner_doc().quirks_mode();
+    dom_apis::element_matches(&element, &selectors, quirks_mode)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SelectorList_QueryFirst(
+    node: &RawGeckoNode,
+    selectors: &SelectorList,
+    may_use_invalidation: bool,
+) -> *const RawGeckoElement {
+    use style::dom_apis::{self, MayUseInvalidation, QueryFirst};
+
+    let node = GeckoNode(node);
+    let mut result = None;
+
+    let may_use_invalidation = if may_use_invalidation {
+        MayUseInvalidation::Yes
+    } else {
+        MayUseInvalidation::No
+    };
+
+    dom_apis::query_selector::<GeckoElement, QueryFirst>(
+        node,
+        &selectors,
+        &mut result,
+        may_use_invalidation,
+    );
+
+    result.map_or(ptr::null(), |e| e.0)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SelectorList_QueryAll(
+    node: &RawGeckoNode,
+    selectors: &SelectorList,
+    content_list: *mut structs::nsSimpleContentList,
+    may_use_invalidation: bool,
+) {
+    use style::dom_apis::{self, MayUseInvalidation, QueryAll};
+
+    let node = GeckoNode(node);
+    let mut result = SmallVec::new();
+
+    let may_use_invalidation = if may_use_invalidation {
+        MayUseInvalidation::Yes
+    } else {
+        MayUseInvalidation::No
+    };
+
+    dom_apis::query_selector::<GeckoElement, QueryAll>(
+        node,
+        &selectors,
+        &mut result,
+        may_use_invalidation,
+    );
+
+    if !result.is_empty() {
+        // NOTE(emilio): This relies on a slice of GeckoElement having the same
+        // memory representation than a slice of element pointers.
+        bindings::Gecko_ContentList_AppendAll(
+            content_list,
+            result.as_ptr() as *mut *const _,
+            result.len(),
+        )
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ImportRule_GetHref(rule: &LockedImportRule, result: &mut nsAString) {
+    read_locked_arc(rule, |rule: &ImportRule| {
+        write!(result, "{}", rule.url.as_str()).unwrap();
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ImportRule_GetLayerName(rule: &LockedImportRule, result: &mut nsACString) {
+    // https://w3c.github.io/csswg-drafts/cssom/#dom-cssimportrule-layername
+    read_locked_arc(rule, |rule: &ImportRule| match rule.layer {
+        ImportLayer::Named(ref name) => name.to_css(&mut CssWriter::new(result)).unwrap(), // "return the layer name declared in the at-rule itself"
+        ImportLayer::Anonymous => {}, // "or an empty string if the layer is anonymous"
+        ImportLayer::None => result.set_is_void(true), // "or null if the at-rule does not declare a layer"
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ImportRule_GetSupportsText(
+    rule: &LockedImportRule,
+    result: &mut nsACString,
+) {
+    read_locked_arc(rule, |rule: &ImportRule| match rule.supports {
+        Some(ref supports) => supports
+            .condition
+            .to_css(&mut CssWriter::new(result))
+            .unwrap(),
+        None => result.set_is_void(true),
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ImportRule_GetSheet(rule: &LockedImportRule) -> *const DomStyleSheet {
+    read_locked_arc(rule, |rule: &ImportRule| {
+        rule.stylesheet
+            .as_sheet()
+            .map_or(ptr::null(), |s| s.raw() as *const DomStyleSheet)
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ImportRule_SetSheet(
+    rule: &LockedImportRule,
+    sheet: *mut DomStyleSheet,
+) {
+    write_locked_arc(rule, |rule: &mut ImportRule| {
+        rule.stylesheet = ImportSheet::new(GeckoStyleSheet::new(sheet));
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Keyframe_GetKeyText(keyframe: &LockedKeyframe, result: &mut nsACString) {
+    read_locked_arc(keyframe, |keyframe: &Keyframe| {
+        keyframe
+            .selector
+            .to_css(&mut CssWriter::new(result))
+            .unwrap()
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Keyframe_SetKeyText(keyframe: &LockedKeyframe, text: &nsACString) -> bool {
+    let text = unsafe { text.as_str_unchecked() };
+    let mut input = ParserInput::new(&text);
+    if let Ok(selector) = Parser::new(&mut input).parse_entirely(KeyframeSelector::parse) {
+        write_locked_arc(keyframe, |keyframe: &mut Keyframe| {
+            keyframe.selector = selector;
+        });
+        true
+    } else {
+        false
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Keyframe_GetStyle(
+    keyframe: &LockedKeyframe,
+) -> Strong<LockedDeclarationBlock> {
+    read_locked_arc(keyframe, |keyframe: &Keyframe| {
+        keyframe.block.clone().into()
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_Keyframe_SetStyle(
+    keyframe: &LockedKeyframe,
+    declarations: &LockedDeclarationBlock,
+) {
+    write_locked_arc(keyframe, |keyframe: &mut Keyframe| {
+        keyframe.block = unsafe { Arc::from_raw_addrefed(declarations) };
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_KeyframesRule_GetName(rule: &LockedKeyframesRule) -> *mut nsAtom {
+    read_locked_arc(rule, |rule: &KeyframesRule| rule.name.as_atom().as_ptr())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_KeyframesRule_SetName(
+    rule: &LockedKeyframesRule,
+    name: *mut nsAtom,
+) {
+    write_locked_arc(rule, |rule: &mut KeyframesRule| {
+        rule.name = KeyframesName::from_atom(Atom::from_addrefed(name));
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_KeyframesRule_GetCount(rule: &LockedKeyframesRule) -> u32 {
+    read_locked_arc(rule, |rule: &KeyframesRule| rule.keyframes.len() as u32)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_KeyframesRule_GetKeyframeAt(
+    rule: &LockedKeyframesRule,
+    index: u32,
+    line: &mut u32,
+    column: &mut u32,
+) -> Strong<LockedKeyframe> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let key = rule.read_with(&guard).keyframes[index as usize].clone();
+    let location = key.read_with(&guard).source_location;
+    *line = location.line as u32;
+    *column = location.column as u32;
+    key.into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_KeyframesRule_FindRule(
+    rule: &LockedKeyframesRule,
+    key: &nsACString,
+) -> u32 {
+    let key = unsafe { key.as_str_unchecked() };
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    rule.read_with(&guard)
+        .find_rule(&guard, key)
+        .map(|index| index as u32)
+        .unwrap_or(u32::max_value())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_KeyframesRule_AppendRule(
+    rule: &LockedKeyframesRule,
+    contents: &StylesheetContents,
+    css: &nsACString,
+) -> bool {
+    let css = unsafe { css.as_str_unchecked() };
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+
+    match Keyframe::parse(css, &contents, &global_style_data.shared_lock) {
+        Ok(keyframe) => {
+            write_locked_arc(rule, |rule: &mut KeyframesRule| {
+                rule.keyframes.push(keyframe);
+            });
+            true
+        },
+        Err(..) => false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_KeyframesRule_DeleteRule(rule: &LockedKeyframesRule, index: u32) {
+    write_locked_arc(rule, |rule: &mut KeyframesRule| {
+        rule.keyframes.remove(index as usize);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaRule_GetMedia(rule: &MediaRule) -> Strong<LockedMediaList> {
+    rule.media_queries.clone().into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_NamespaceRule_GetPrefix(rule: &NamespaceRule) -> *mut nsAtom {
+    rule.prefix
+        .as_ref()
+        .map_or(atom!("").as_ptr(), |a| a.as_ptr())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_NamespaceRule_GetURI(rule: &NamespaceRule) -> *mut nsAtom {
+    rule.url.0.as_ptr()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PageRule_GetStyle(rule: &LockedPageRule) -> Strong<LockedDeclarationBlock> {
+    read_locked_arc(rule, |rule: &PageRule| rule.block.clone().into())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PageRule_SetStyle(
+    rule: &LockedPageRule,
+    declarations: &LockedDeclarationBlock,
+) {
+    write_locked_arc(rule, |rule: &mut PageRule| {
+        rule.block = unsafe { Arc::from_raw_addrefed(declarations) };
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PageRule_GetSelectorText(rule: &LockedPageRule, result: &mut nsACString) {
+    read_locked_arc(rule, |rule: &PageRule| {
+        rule.selectors.to_css(&mut CssWriter::new(result)).unwrap();
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PageRule_SetSelectorText(
+    contents: &StylesheetContents,
+    rule: &LockedPageRule,
+    text: &nsACString,
+) -> bool {
+    let value_str = unsafe { text.as_str_unchecked() };
+
+    write_locked_arc(rule, |rule: &mut PageRule| {
+        use style::stylesheets::PageSelectors;
+
+        let mut parser_input = ParserInput::new(&value_str);
+        let mut parser = Parser::new(&mut parser_input);
+
+        // Ensure that a blank input results in empty page selectors
+        if parser.is_exhausted() {
+            rule.selectors = PageSelectors::default();
+            return true;
+        }
+
+        let url_data = contents.url_data.read();
+        let context = ParserContext::new(
+            Origin::Author,
+            &url_data,
+            None,
+            ParsingMode::DEFAULT,
+            QuirksMode::NoQuirks,
+            /* namespaces = */ Default::default(),
+            None,
+            None,
+        );
+
+        match parser.parse_entirely(|i| PageSelectors::parse(&context, i)) {
+            Ok(selectors) => {
+                rule.selectors = selectors;
+                true
+            },
+            Err(_) => false,
+        }
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PropertyRule_GetName(rule: &PropertyRule, result: &mut nsACString) {
+    write!(result, "--{}", rule.name.0).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PropertyRule_GetSyntax(rule: &PropertyRule, result: &mut nsACString) {
+    if let Some(syntax) = rule.data.syntax.specified_string() {
+        result.assign(syntax);
+    } else {
+        debug_assert!(false, "Rule without specified syntax?");
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PropertyRule_GetInherits(rule: &PropertyRule) -> bool {
+    rule.inherits()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_PropertyRule_GetInitialValue(
+    rule: &PropertyRule,
+    result: &mut nsACString,
+) -> bool {
+    rule.data
+        .initial_value
+        .to_css(&mut CssWriter::new(result))
+        .unwrap();
+    rule.data.initial_value.is_some()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_SupportsRule_GetConditionText(
+    rule: &SupportsRule,
+    result: &mut nsACString,
+) {
+    rule.condition.to_css(&mut CssWriter::new(result)).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ContainerRule_GetConditionText(
+    rule: &ContainerRule,
+    result: &mut nsACString,
+) {
+    rule.condition.to_css(&mut CssWriter::new(result)).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ContainerRule_GetContainerQuery(
+    rule: &ContainerRule,
+    result: &mut nsACString,
+) {
+    rule.query_condition()
+        .to_css(&mut CssWriter::new(result))
+        .unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ContainerRule_QueryContainerFor(
+    rule: &ContainerRule,
+    element: &RawGeckoElement,
+) -> *const RawGeckoElement {
+    rule.condition
+        .find_container(GeckoElement(element), None)
+        .map_or(ptr::null(), |result| result.element.0)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ContainerRule_GetContainerName(
+    rule: &ContainerRule,
+    result: &mut nsACString,
+) {
+    let name = rule.container_name();
+    if !name.is_none() {
+        name.to_css(&mut CssWriter::new(result)).unwrap();
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DocumentRule_GetConditionText(
+    rule: &DocumentRule,
+    result: &mut nsACString,
+) {
+    rule.condition.to_css(&mut CssWriter::new(result)).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFeatureValuesRule_GetFontFamily(
+    rule: &FontFeatureValuesRule,
+    result: &mut nsACString,
+) {
+    rule.family_names
+        .to_css(&mut CssWriter::new(result))
+        .unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFeatureValuesRule_GetValueText(
+    rule: &FontFeatureValuesRule,
+    result: &mut nsACString,
+) {
+    rule.value_to_css(&mut CssWriter::new(result)).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontPaletteValuesRule_GetName(
+    rule: &FontPaletteValuesRule,
+    result: &mut nsACString,
+) {
+    rule.name.to_css(&mut CssWriter::new(result)).unwrap()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontPaletteValuesRule_GetFontFamily(
+    rule: &FontPaletteValuesRule,
+    result: &mut nsACString,
+) {
+    if !rule.family_names.is_empty() {
+        rule.family_names
+            .to_css(&mut CssWriter::new(result))
+            .unwrap()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontPaletteValuesRule_GetBasePalette(
+    rule: &FontPaletteValuesRule,
+    result: &mut nsACString,
+) {
+    rule.base_palette
+        .to_css(&mut CssWriter::new(result))
+        .unwrap()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontPaletteValuesRule_GetOverrideColors(
+    rule: &FontPaletteValuesRule,
+    result: &mut nsACString,
+) {
+    if !rule.override_colors.is_empty() {
+        rule.override_colors
+            .to_css(&mut CssWriter::new(result))
+            .unwrap()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_CreateEmpty() -> Strong<LockedFontFaceRule> {
+    // XXX This is not great. We should split FontFace descriptor data
+    // from the rule, so that we don't need to create the rule like this
+    // and the descriptor data itself can be hold in UniquePtr from the
+    // Gecko side. See bug 1450904.
+    with_maybe_worker_shared_lock(|lock| {
+        Arc::new(lock.wrap(FontFaceRule::empty(SourceLocation { line: 0, column: 0 }))).into()
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_Clone(
+    rule: &LockedFontFaceRule,
+) -> Strong<LockedFontFaceRule> {
+    let clone = read_locked_arc_worker(rule, |rule: &FontFaceRule| rule.clone());
+    with_maybe_worker_shared_lock(|lock| Arc::new(lock.wrap(clone)).into())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetSourceLocation(
+    rule: &LockedFontFaceRule,
+    line: *mut u32,
+    column: *mut u32,
+) {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let location = rule.source_location;
+        *line.as_mut().unwrap() = location.line as u32;
+        *column.as_mut().unwrap() = location.column as u32;
+    });
+}
+
+macro_rules! apply_font_desc_list {
+    ($apply_macro:ident) => {
+        $apply_macro! {
+            valid: [
+                eCSSFontDesc_Family => family,
+                eCSSFontDesc_Style => style,
+                eCSSFontDesc_Weight => weight,
+                eCSSFontDesc_Stretch => stretch,
+                eCSSFontDesc_Src => sources,
+                eCSSFontDesc_UnicodeRange => unicode_range,
+                eCSSFontDesc_FontFeatureSettings => feature_settings,
+                eCSSFontDesc_FontVariationSettings => variation_settings,
+                eCSSFontDesc_FontLanguageOverride => language_override,
+                eCSSFontDesc_Display => display,
+                eCSSFontDesc_AscentOverride => ascent_override,
+                eCSSFontDesc_DescentOverride => descent_override,
+                eCSSFontDesc_LineGapOverride => line_gap_override,
+                eCSSFontDesc_SizeAdjust => size_adjust,
+            ]
+            invalid: [
+                eCSSFontDesc_UNKNOWN,
+                eCSSFontDesc_COUNT,
+            ]
+        }
+    };
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_Length(rule: &LockedFontFaceRule) -> u32 {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let mut result = 0;
+        macro_rules! count_values {
+            (
+                valid: [$($v_enum_name:ident => $field:ident,)*]
+                invalid: [$($i_enum_name:ident,)*]
+            ) => {
+                $(if rule.$field.is_some() {
+                    result += 1;
+                })*
+            }
+        }
+        apply_font_desc_list!(count_values);
+        result
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_IndexGetter(
+    rule: &LockedFontFaceRule,
+    index: u32,
+) -> nsCSSFontDesc {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let mut count = 0;
+        macro_rules! lookup_index {
+            (
+                valid: [$($v_enum_name:ident => $field:ident,)*]
+                invalid: [$($i_enum_name:ident,)*]
+            ) => {
+                $(if rule.$field.is_some() {
+                    count += 1;
+                    if count - 1 == index {
+                        return nsCSSFontDesc::$v_enum_name;
+                    }
+                })*
+            }
+        }
+        apply_font_desc_list!(lookup_index);
+        return nsCSSFontDesc::eCSSFontDesc_UNKNOWN;
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetDeclCssText(
+    rule: &LockedFontFaceRule,
+    result: &mut nsACString,
+) {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        rule.decl_to_css(result).unwrap();
+    })
+}
+
+macro_rules! simple_font_descriptor_getter_impl {
+    ($rule:ident, $out:ident, $field:ident, $compute:ident) => {
+        read_locked_arc_worker($rule, |rule: &FontFaceRule| {
+            match rule.$field {
+                None => return false,
+                Some(ref f) => *$out = f.$compute(),
+            }
+            true
+        })
+    };
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetFontWeight(
+    rule: &LockedFontFaceRule,
+    out: &mut font_face::ComputedFontWeightRange,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, weight, compute)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetFontStretch(
+    rule: &LockedFontFaceRule,
+    out: &mut font_face::ComputedFontStretchRange,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, stretch, compute)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetFontStyle(
+    rule: &LockedFontFaceRule,
+    out: &mut font_face::ComputedFontStyleDescriptor,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, style, compute)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetFontDisplay(
+    rule: &LockedFontFaceRule,
+    out: &mut font_face::FontDisplay,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, display, clone)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetFontLanguageOverride(
+    rule: &LockedFontFaceRule,
+    out: &mut computed::FontLanguageOverride,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, language_override, clone)
+}
+
+// Returns a Percentage of -1.0 if the override descriptor is present but 'normal'
+// rather than an actual percentage value.
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetAscentOverride(
+    rule: &LockedFontFaceRule,
+    out: &mut computed::Percentage,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, ascent_override, compute)
+}
+
+// Returns a Percentage of -1.0 if the override descriptor is present but 'normal'
+// rather than an actual percentage value.
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetDescentOverride(
+    rule: &LockedFontFaceRule,
+    out: &mut computed::Percentage,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, descent_override, compute)
+}
+
+// Returns a Percentage of -1.0 if the override descriptor is present but 'normal'
+// rather than an actual percentage value.
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetLineGapOverride(
+    rule: &LockedFontFaceRule,
+    out: &mut computed::Percentage,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, line_gap_override, compute)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetSizeAdjust(
+    rule: &LockedFontFaceRule,
+    out: &mut computed::Percentage,
+) -> bool {
+    simple_font_descriptor_getter_impl!(rule, out, size_adjust, compute)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetFamilyName(
+    rule: &LockedFontFaceRule,
+) -> *mut nsAtom {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        // TODO(emilio): font-family is a mandatory descriptor, can't we unwrap
+        // here, and remove the null-checks in Gecko?
+        rule.family
+            .as_ref()
+            .map_or(ptr::null_mut(), |f| f.name.as_ptr())
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetUnicodeRanges(
+    rule: &LockedFontFaceRule,
+    out_len: *mut usize,
+) -> *const UnicodeRange {
+    *out_len = 0;
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let ranges = match rule.unicode_range {
+            Some(ref ranges) => ranges,
+            None => return ptr::null(),
+        };
+        *out_len = ranges.len();
+        ranges.as_ptr() as *const _
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetSources(
+    rule: &LockedFontFaceRule,
+    out: *mut nsTArray<FontFaceSourceListComponent>,
+) {
+    let out = &mut *out;
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let sources = match rule.sources {
+            Some(ref s) => s,
+            None => return,
+        };
+        let len = sources.0.iter().fold(0, |acc, src| {
+            acc + match *src {
+                Source::Url(ref url) => {
+                    (if url.format_hint.is_some() { 2 } else { 1 }) +
+                        (if url.tech_flags.is_empty() { 0 } else { 1 })
+                },
+                Source::Local(_) => 1,
+            }
+        });
+
+        out.set_len(len as u32);
+
+        let mut iter = out.iter_mut();
+
+        {
+            let mut set_next = |component: FontFaceSourceListComponent| {
+                *iter.next().expect("miscalculated length") = component;
+            };
+
+            for source in sources.0.iter() {
+                match *source {
+                    Source::Url(ref url) => {
+                        set_next(FontFaceSourceListComponent::Url(&url.url));
+                        if let Some(hint) = &url.format_hint {
+                            match hint {
+                                FontFaceSourceFormat::Keyword(kw) => {
+                                    set_next(FontFaceSourceListComponent::FormatHintKeyword(*kw))
+                                },
+                                FontFaceSourceFormat::String(s) => {
+                                    set_next(FontFaceSourceListComponent::FormatHintString {
+                                        length: s.len(),
+                                        utf8_bytes: s.as_ptr(),
+                                    })
+                                },
+                            }
+                        }
+                        if !url.tech_flags.is_empty() {
+                            set_next(FontFaceSourceListComponent::TechFlags(url.tech_flags));
+                        }
+                    },
+                    Source::Local(ref name) => {
+                        set_next(FontFaceSourceListComponent::Local(name.name.as_ptr()));
+                    },
+                }
+            }
+        }
+
+        assert!(iter.next().is_none(), "miscalculated");
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetVariationSettings(
+    rule: &LockedFontFaceRule,
+    variations: *mut nsTArray<structs::gfxFontVariation>,
+) {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let source_variations = match rule.variation_settings {
+            Some(ref v) => v,
+            None => return,
+        };
+
+        (*variations).set_len(source_variations.0.len() as u32);
+        for (target, source) in (*variations).iter_mut().zip(source_variations.0.iter()) {
+            *target = structs::gfxFontVariation {
+                mTag: source.tag.0,
+                mValue: source.value.get(),
+            };
+        }
+    });
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_GetFeatureSettings(
+    rule: &LockedFontFaceRule,
+    features: *mut nsTArray<structs::gfxFontFeature>,
+) {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let source_features = match rule.feature_settings {
+            Some(ref v) => v,
+            None => return,
+        };
+
+        (*features).set_len(source_features.0.len() as u32);
+        for (target, source) in (*features).iter_mut().zip(source_features.0.iter()) {
+            *target = structs::gfxFontFeature {
+                mTag: source.tag.0,
+                mValue: source.value.value() as u32,
+            };
+        }
+    });
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFaceRule_GetDescriptorCssText(
+    rule: &LockedFontFaceRule,
+    desc: nsCSSFontDesc,
+    result: &mut nsACString,
+) {
+    read_locked_arc_worker(rule, |rule: &FontFaceRule| {
+        let mut writer = CssWriter::new(result);
+        macro_rules! to_css_text {
+            (
+                valid: [$($v_enum_name:ident => $field:ident,)*]
+                invalid: [$($i_enum_name:ident,)*]
+            ) => {
+                match desc {
+                    $(
+                        nsCSSFontDesc::$v_enum_name => {
+                            if let Some(ref value) = rule.$field {
+                                value.to_css(&mut writer).unwrap();
+                            }
+                        }
+                    )*
+                    $(
+                        nsCSSFontDesc::$i_enum_name => {
+                            debug_assert!(false, "not a valid font descriptor");
+                        }
+                    )*
+                }
+            }
+        }
+        apply_font_desc_list!(to_css_text)
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_SetDescriptor(
+    rule: &LockedFontFaceRule,
+    desc: nsCSSFontDesc,
+    value: &nsACString,
+    data: *mut URLExtraData,
+    out_changed: *mut bool,
+) -> bool {
+    let value = value.as_str_unchecked();
+    let mut input = ParserInput::new(&value);
+    let mut parser = Parser::new(&mut input);
+    let url_data = UrlExtraData::from_ptr_ref(&data);
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        Some(CssRuleType::FontFace),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    write_locked_arc_worker(rule, |rule: &mut FontFaceRule| {
+        macro_rules! to_css_text {
+            (
+                valid: [$($v_enum_name:ident => $field:ident,)*]
+                invalid: [$($i_enum_name:ident,)*]
+            ) => {
+                match desc {
+                    $(
+                        nsCSSFontDesc::$v_enum_name => {
+                            if let Ok(value) = parser.parse_entirely(|i| Parse::parse(&context, i)) {
+                                let result = Some(value);
+                                *out_changed = result != rule.$field;
+                                rule.$field = result;
+                                true
+                            } else {
+                                false
+                            }
+                        }
+                    )*
+                    $(
+                        nsCSSFontDesc::$i_enum_name => {
+                            debug_assert!(false, "not a valid font descriptor");
+                            false
+                        }
+                    )*
+                }
+            }
+        }
+        apply_font_desc_list!(to_css_text)
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_FontFaceRule_ResetDescriptor(
+    rule: &LockedFontFaceRule,
+    desc: nsCSSFontDesc,
+) {
+    write_locked_arc_worker(rule, |rule: &mut FontFaceRule| {
+        macro_rules! reset_desc {
+            (
+                valid: [$($v_enum_name:ident => $field:ident,)*]
+                invalid: [$($i_enum_name:ident,)*]
+            ) => {
+                match desc {
+                    $(nsCSSFontDesc::$v_enum_name => rule.$field = None,)*
+                    $(nsCSSFontDesc::$i_enum_name => debug_assert!(false, "not a valid font descriptor"),)*
+                }
+            }
+        }
+        apply_font_desc_list!(reset_desc)
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetName(
+    rule: &LockedCounterStyleRule,
+) -> *mut nsAtom {
+    read_locked_arc(rule, |rule: &CounterStyleRule| rule.name().0.as_ptr())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_SetName(
+    rule: &LockedCounterStyleRule,
+    value: &nsACString,
+) -> bool {
+    let value = value.as_str_unchecked();
+    let mut input = ParserInput::new(&value);
+    let mut parser = Parser::new(&mut input);
+    match parser.parse_entirely(counter_style::parse_counter_style_name_definition) {
+        Ok(name) => {
+            write_locked_arc(rule, |rule: &mut CounterStyleRule| rule.set_name(name));
+            true
+        },
+        Err(_) => false,
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetGeneration(
+    rule: &LockedCounterStyleRule,
+) -> u32 {
+    read_locked_arc(rule, |rule: &CounterStyleRule| rule.generation())
+}
+
+fn symbol_to_string(s: &counter_style::Symbol) -> nsString {
+    match *s {
+        counter_style::Symbol::String(ref s) => nsString::from(&**s),
+        counter_style::Symbol::Ident(ref i) => nsString::from(i.0.as_slice()),
+    }
+}
+
+// TODO(emilio): Cbindgen could be used to simplify a bunch of code here.
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetPad(
+    rule: &LockedCounterStyleRule,
+    width: &mut i32,
+    symbol: &mut nsString,
+) -> bool {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        let pad = match rule.pad() {
+            Some(pad) => pad,
+            None => return false,
+        };
+        *width = pad.0.value();
+        *symbol = symbol_to_string(&pad.1);
+        true
+    })
+}
+
+fn get_symbol(s: Option<&counter_style::Symbol>, out: &mut nsString) -> bool {
+    let s = match s {
+        Some(s) => s,
+        None => return false,
+    };
+    *out = symbol_to_string(s);
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetPrefix(
+    rule: &LockedCounterStyleRule,
+    out: &mut nsString,
+) -> bool {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        get_symbol(rule.prefix(), out)
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetSuffix(
+    rule: &LockedCounterStyleRule,
+    out: &mut nsString,
+) -> bool {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        get_symbol(rule.suffix(), out)
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetNegative(
+    rule: &LockedCounterStyleRule,
+    prefix: &mut nsString,
+    suffix: &mut nsString,
+) -> bool {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        let negative = match rule.negative() {
+            Some(n) => n,
+            None => return false,
+        };
+        *prefix = symbol_to_string(&negative.0);
+        *suffix = match negative.1 {
+            Some(ref s) => symbol_to_string(s),
+            None => nsString::new(),
+        };
+        true
+    })
+}
+
+#[repr(u8)]
+pub enum IsOrdinalInRange {
+    Auto,
+    InRange,
+    NotInRange,
+    NoOrdinalSpecified,
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_IsInRange(
+    rule: &LockedCounterStyleRule,
+    ordinal: i32,
+) -> IsOrdinalInRange {
+    use style::counter_style::CounterBound;
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        let range = match rule.range() {
+            Some(r) => r,
+            None => return IsOrdinalInRange::NoOrdinalSpecified,
+        };
+
+        if range.0.is_empty() {
+            return IsOrdinalInRange::Auto;
+        }
+
+        let in_range = range.0.iter().any(|r| {
+            if let CounterBound::Integer(start) = r.start {
+                if start.value() > ordinal {
+                    return false;
+                }
+            }
+
+            if let CounterBound::Integer(end) = r.end {
+                if end.value() < ordinal {
+                    return false;
+                }
+            }
+
+            true
+        });
+
+        if in_range {
+            IsOrdinalInRange::InRange
+        } else {
+            IsOrdinalInRange::NotInRange
+        }
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetSymbols(
+    rule: &LockedCounterStyleRule,
+    symbols: &mut style::OwnedSlice<nsString>,
+) {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        *symbols = match rule.symbols() {
+            Some(s) => s.0.iter().map(symbol_to_string).collect(),
+            None => style::OwnedSlice::default(),
+        };
+    })
+}
+
+#[repr(C)]
+pub struct AdditiveSymbol {
+    pub weight: i32,
+    pub symbol: nsString,
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetAdditiveSymbols(
+    rule: &LockedCounterStyleRule,
+    symbols: &mut style::OwnedSlice<AdditiveSymbol>,
+) {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        *symbols = match rule.additive_symbols() {
+            Some(s) => {
+                s.0.iter()
+                    .map(|s| AdditiveSymbol {
+                        weight: s.weight.value(),
+                        symbol: symbol_to_string(&s.symbol),
+                    })
+                    .collect()
+            },
+            None => style::OwnedSlice::default(),
+        };
+    })
+}
+
+#[repr(C, u8)]
+pub enum CounterSpeakAs {
+    None,
+    Auto,
+    Bullets,
+    Numbers,
+    Words,
+    Ident(*mut nsAtom),
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetSpeakAs(
+    rule: &LockedCounterStyleRule,
+    out: &mut CounterSpeakAs,
+) {
+    use style::counter_style::SpeakAs;
+    *out = read_locked_arc(rule, |rule: &CounterStyleRule| {
+        let speak_as = match rule.speak_as() {
+            Some(s) => s,
+            None => return CounterSpeakAs::None,
+        };
+        match *speak_as {
+            SpeakAs::Auto => CounterSpeakAs::Auto,
+            SpeakAs::Bullets => CounterSpeakAs::Bullets,
+            SpeakAs::Numbers => CounterSpeakAs::Numbers,
+            SpeakAs::Words => CounterSpeakAs::Words,
+            SpeakAs::Other(ref other) => CounterSpeakAs::Ident(other.0.as_ptr()),
+        }
+    });
+}
+
+#[repr(u8)]
+pub enum CounterSystem {
+    Cyclic = 0,
+    Numeric,
+    Alphabetic,
+    Symbolic,
+    Additive,
+    Fixed,
+    Extends,
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetSystem(
+    rule: &LockedCounterStyleRule,
+) -> CounterSystem {
+    use style::counter_style::System;
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        match *rule.resolved_system() {
+            System::Cyclic => CounterSystem::Cyclic,
+            System::Numeric => CounterSystem::Numeric,
+            System::Alphabetic => CounterSystem::Alphabetic,
+            System::Symbolic => CounterSystem::Symbolic,
+            System::Additive => CounterSystem::Additive,
+            System::Fixed { .. } => CounterSystem::Fixed,
+            System::Extends(_) => CounterSystem::Extends,
+        }
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetExtended(
+    rule: &LockedCounterStyleRule,
+) -> *mut nsAtom {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        match *rule.resolved_system() {
+            counter_style::System::Extends(ref name) => name.0.as_ptr(),
+            _ => {
+                debug_assert!(false, "Not extends system");
+                ptr::null_mut()
+            },
+        }
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetFixedFirstValue(
+    rule: &LockedCounterStyleRule,
+) -> i32 {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        match *rule.resolved_system() {
+            counter_style::System::Fixed { first_symbol_value } => {
+                first_symbol_value.map_or(1, |v| v.value())
+            },
+            _ => {
+                debug_assert!(false, "Not fixed system");
+                0
+            },
+        }
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CounterStyleRule_GetFallback(
+    rule: &LockedCounterStyleRule,
+) -> *mut nsAtom {
+    read_locked_arc(rule, |rule: &CounterStyleRule| {
+        rule.fallback().map_or(ptr::null_mut(), |i| i.0 .0.as_ptr())
+    })
+}
+
+macro_rules! counter_style_descriptors {
+    {
+        valid: [
+            $($desc:ident => $getter:ident / $setter:ident,)+
+        ]
+        invalid: [
+            $($i_desc:ident,)+
+        ]
+    } => {
+        #[no_mangle]
+        pub unsafe extern "C" fn Servo_CounterStyleRule_GetDescriptorCssText(
+            rule: &LockedCounterStyleRule,
+            desc: nsCSSCounterDesc,
+            result: &mut nsACString,
+        ) {
+            let mut writer = CssWriter::new(result);
+            read_locked_arc(rule, |rule: &CounterStyleRule| {
+                match desc {
+                    $(nsCSSCounterDesc::$desc => {
+                        if let Some(value) = rule.$getter() {
+                            value.to_css(&mut writer).unwrap();
+                        }
+                    })+
+                    $(nsCSSCounterDesc::$i_desc => unreachable!(),)+
+                }
+            });
+        }
+
+        #[no_mangle]
+        pub unsafe extern "C" fn Servo_CounterStyleRule_SetDescriptor(
+            rule: &LockedCounterStyleRule,
+            desc: nsCSSCounterDesc,
+            value: &nsACString,
+        ) -> bool {
+            let value = value.as_str_unchecked();
+            let mut input = ParserInput::new(&value);
+            let mut parser = Parser::new(&mut input);
+            let url_data = dummy_url_data();
+            let context = ParserContext::new(
+                Origin::Author,
+                url_data,
+                Some(CssRuleType::CounterStyle),
+                ParsingMode::DEFAULT,
+                QuirksMode::NoQuirks,
+                /* namespaces = */ Default::default(),
+                None,
+                None,
+            );
+
+            write_locked_arc(rule, |rule: &mut CounterStyleRule| {
+                match desc {
+                    $(nsCSSCounterDesc::$desc => {
+                        match parser.parse_entirely(|i| Parse::parse(&context, i)) {
+                            Ok(value) => rule.$setter(value),
+                            Err(_) => false,
+                        }
+                    })+
+                    $(nsCSSCounterDesc::$i_desc => unreachable!(),)+
+                }
+            })
+        }
+    }
+}
+
+counter_style_descriptors! {
+    valid: [
+        eCSSCounterDesc_System => system / set_system,
+        eCSSCounterDesc_Symbols => symbols / set_symbols,
+        eCSSCounterDesc_AdditiveSymbols => additive_symbols / set_additive_symbols,
+        eCSSCounterDesc_Negative => negative / set_negative,
+        eCSSCounterDesc_Prefix => prefix / set_prefix,
+        eCSSCounterDesc_Suffix => suffix / set_suffix,
+        eCSSCounterDesc_Range => range / set_range,
+        eCSSCounterDesc_Pad => pad / set_pad,
+        eCSSCounterDesc_Fallback => fallback / set_fallback,
+        eCSSCounterDesc_SpeakAs => speak_as / set_speak_as,
+    ]
+    invalid: [
+        eCSSCounterDesc_UNKNOWN,
+        eCSSCounterDesc_COUNT,
+    ]
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ComputedValues_GetForPageContent(
+    raw_data: &PerDocumentStyleData,
+    page_name: *const nsAtom,
+    pseudos: PagePseudoClassFlags,
+) -> Strong<ComputedValues> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let guards = StylesheetGuards::same(&guard);
+    let data = raw_data.borrow_mut();
+    let cascade_data = data.stylist.cascade_data();
+
+    let mut extra_declarations = vec![];
+    let iter = data.stylist.iter_extra_data_origins_rev();
+    let name = if !page_name.is_null() {
+        Some(Atom::from_raw(page_name as *mut nsAtom))
+    } else {
+        None
+    };
+    for (data, origin) in iter {
+        data.pages.match_and_append_rules(
+            &mut extra_declarations,
+            origin,
+            &guards,
+            cascade_data,
+            &name,
+            pseudos,
+        );
+    }
+
+    let rule_node = data.stylist.rule_node_for_precomputed_pseudo(
+        &guards,
+        &PseudoElement::PageContent,
+        extra_declarations,
+    );
+
+    data.stylist
+        .precomputed_values_for_pseudo_with_rule_node::<GeckoElement>(
+            &guards,
+            &PseudoElement::PageContent,
+            None,
+            rule_node,
+        )
+        .into()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ComputedValues_GetForAnonymousBox(
+    parent_style_or_null: Option<&ComputedValues>,
+    pseudo: PseudoStyleType,
+    raw_data: &PerDocumentStyleData,
+) -> Strong<ComputedValues> {
+    let pseudo = PseudoElement::from_pseudo_type(pseudo, None).unwrap();
+    debug_assert!(pseudo.is_anon_box());
+    debug_assert_ne!(pseudo, PseudoElement::PageContent);
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let guards = StylesheetGuards::same(&guard);
+    let data = raw_data.borrow_mut();
+    let rule_node = data
+        .stylist
+        .rule_node_for_precomputed_pseudo(&guards, &pseudo, vec![]);
+
+    data.stylist
+        .precomputed_values_for_pseudo_with_rule_node::<GeckoElement>(
+            &guards,
+            &pseudo,
+            parent_style_or_null.map(|x| &*x),
+            rule_node,
+        )
+        .into()
+}
+
+fn get_functional_pseudo_parameter_atom(
+    functional_pseudo_parameter: *mut nsAtom,
+) -> Option<AtomIdent> {
+    if functional_pseudo_parameter.is_null() {
+        None
+    } else {
+        Some(AtomIdent::new(unsafe {
+            Atom::from_raw(functional_pseudo_parameter)
+        }))
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ResolvePseudoStyle(
+    element: &RawGeckoElement,
+    pseudo_type: PseudoStyleType,
+    functional_pseudo_parameter: *mut nsAtom,
+    is_probe: bool,
+    inherited_style: Option<&ComputedValues>,
+    raw_data: &PerDocumentStyleData,
+) -> Strong<ComputedValues> {
+    let element = GeckoElement(element);
+    let doc_data = raw_data.borrow();
+
+    debug!(
+        "Servo_ResolvePseudoStyle: {:?} {:?}, is_probe: {}",
+        element,
+        PseudoElement::from_pseudo_type(
+            pseudo_type,
+            get_functional_pseudo_parameter_atom(functional_pseudo_parameter)
+        ),
+        is_probe
+    );
+
+    let data = element.borrow_data();
+
+    let data = match data.as_ref() {
+        Some(data) if data.has_styles() => data,
+        _ => {
+            // FIXME(bholley, emilio): Assert against this.
+            //
+            // Known offender is nsMathMLmoFrame::MarkIntrinsicISizesDirty,
+            // which goes and does a bunch of work involving style resolution.
+            //
+            // Bug 1403865 tracks fixing it, and potentially adding an assert
+            // here instead.
+            warn!("Calling Servo_ResolvePseudoStyle on unstyled element");
+            return if is_probe {
+                Strong::null()
+            } else {
+                doc_data.default_computed_values().clone().into()
+            };
+        },
+    };
+
+    let pseudo_element = PseudoElement::from_pseudo_type(
+        pseudo_type,
+        get_functional_pseudo_parameter_atom(functional_pseudo_parameter),
+    )
+    .expect("ResolvePseudoStyle with a non-pseudo?");
+
+    let matching_fn = |pseudo: &PseudoElement| *pseudo == pseudo_element;
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let style = get_pseudo_style(
+        &guard,
+        element,
+        &pseudo_element,
+        RuleInclusion::All,
+        &data.styles,
+        inherited_style,
+        &doc_data.stylist,
+        is_probe,
+        /* matching_func = */
+        if pseudo_element.is_highlight() {
+            Some(&matching_fn)
+        } else {
+            None
+        },
+    );
+
+    match style {
+        Some(s) => s.into(),
+        None => {
+            debug_assert!(is_probe);
+            Strong::null()
+        },
+    }
+}
+
+fn debug_atom_array(atoms: &nsTArray<structs::RefPtr<nsAtom>>) -> String {
+    let mut result = String::from("[");
+    for atom in atoms.iter() {
+        if atom.mRawPtr.is_null() {
+            result += "(null), ";
+        } else {
+            let atom = unsafe { WeakAtom::new(atom.mRawPtr) };
+            write!(result, "{}, ", atom).unwrap();
+        }
+    }
+    result.push(']');
+    result
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_ResolveXULTreePseudoStyle(
+    element: &RawGeckoElement,
+    pseudo_tag: *mut nsAtom,
+    inherited_style: &ComputedValues,
+    input_word: &nsTArray<structs::RefPtr<nsAtom>>,
+    raw_data: &PerDocumentStyleData,
+) -> Strong<ComputedValues> {
+    let element = GeckoElement(element);
+    let data = element
+        .borrow_data()
+        .expect("Calling ResolveXULTreePseudoStyle on unstyled element?");
+
+    let pseudo = unsafe {
+        Atom::with(pseudo_tag, |atom| {
+            PseudoElement::from_tree_pseudo_atom(atom, Box::new([]))
+        })
+        .expect("ResolveXULTreePseudoStyle with a non-tree pseudo?")
+    };
+    let doc_data = raw_data.borrow();
+
+    debug!(
+        "ResolveXULTreePseudoStyle: {:?} {:?} {}",
+        element,
+        pseudo,
+        debug_atom_array(input_word)
+    );
+
+    let matching_fn = |pseudo: &PseudoElement| {
+        let args = pseudo
+            .tree_pseudo_args()
+            .expect("Not a tree pseudo-element?");
+        args.iter()
+            .all(|atom| input_word.iter().any(|item| atom.as_ptr() == item.mRawPtr))
+    };
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    get_pseudo_style(
+        &guard,
+        element,
+        &pseudo,
+        RuleInclusion::All,
+        &data.styles,
+        Some(inherited_style),
+        &doc_data.stylist,
+        /* is_probe = */ false,
+        Some(&matching_fn),
+    )
+    .unwrap()
+    .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_SetExplicitStyle(element: &RawGeckoElement, style: &ComputedValues) {
+    let element = GeckoElement(element);
+    debug!("Servo_SetExplicitStyle: {:?}", element);
+    // We only support this API for initial styling. There's no reason it couldn't
+    // work for other things, we just haven't had a reason to do so.
+    debug_assert!(!element.has_data());
+    let mut data = unsafe { element.ensure_data() };
+    data.styles.primary = Some(unsafe { Arc::from_raw_addrefed(style) });
+}
+
+fn get_pseudo_style(
+    guard: &SharedRwLockReadGuard,
+    element: GeckoElement,
+    pseudo: &PseudoElement,
+    rule_inclusion: RuleInclusion,
+    styles: &ElementStyles,
+    inherited_styles: Option<&ComputedValues>,
+    stylist: &Stylist,
+    is_probe: bool,
+    matching_func: Option<&dyn Fn(&PseudoElement) -> bool>,
+) -> Option<Arc<ComputedValues>> {
+    let style = match pseudo.cascade_type() {
+        PseudoElementCascadeType::Eager => {
+            match *pseudo {
+                PseudoElement::FirstLetter => {
+                    styles.pseudos.get(&pseudo).map(|pseudo_styles| {
+                        // inherited_styles can be None when doing lazy resolution
+                        // (e.g. for computed style) or when probing.  In that case
+                        // we just inherit from our element, which is what Gecko
+                        // does in that situation.  What should actually happen in
+                        // the computed style case is a bit unclear.
+                        let inherited_styles = inherited_styles.unwrap_or(styles.primary());
+                        let guards = StylesheetGuards::same(guard);
+                        let inputs = CascadeInputs::new_from_style(pseudo_styles);
+                        stylist.compute_pseudo_element_style_with_inputs(
+                            inputs,
+                            pseudo,
+                            &guards,
+                            Some(inherited_styles),
+                            Some(element),
+                        )
+                    })
+                },
+                _ => {
+                    // Unfortunately, we can't assert that inherited_styles, if
+                    // present, is pointer-equal to styles.primary(), or even
+                    // equal in any meaningful way.  The way it can fail is as
+                    // follows.  Say we append an element with a ::before,
+                    // ::after, or ::first-line to a parent with a ::first-line,
+                    // such that the element ends up on the first line of the
+                    // parent (e.g. it's an inline-block in the case it has a
+                    // ::first-line, or any container in the ::before/::after
+                    // cases).  Then gecko will update its frame's style to
+                    // inherit from the parent's ::first-line.  The next time we
+                    // try to get the ::before/::after/::first-line style for
+                    // the kid, we'll likely pass in the frame's style as
+                    // inherited_styles, but that's not pointer-identical to
+                    // styles.primary(), because it got reparented.
+                    //
+                    // Now in practice this turns out to be OK, because all the
+                    // cases in which there's a mismatch go ahead and reparent
+                    // styles again as needed to make sure the ::first-line
+                    // affects all the things it should affect.  But it makes it
+                    // impossible to assert anything about the two styles
+                    // matching here, unfortunately.
+                    styles.pseudos.get(&pseudo).cloned()
+                },
+            }
+        },
+        PseudoElementCascadeType::Precomputed => unreachable!("No anonymous boxes"),
+        PseudoElementCascadeType::Lazy => {
+            debug_assert!(
+                inherited_styles.is_none() ||
+                    ptr::eq(inherited_styles.unwrap(), &**styles.primary())
+            );
+            let originating_element_style = styles.primary();
+            let guards = StylesheetGuards::same(guard);
+            stylist.lazily_compute_pseudo_element_style(
+                &guards,
+                element,
+                &pseudo,
+                rule_inclusion,
+                originating_element_style,
+                is_probe,
+                matching_func,
+            )
+        },
+    };
+
+    if is_probe {
+        return style;
+    }
+
+    Some(style.unwrap_or_else(|| {
+        StyleBuilder::for_inheritance(
+            stylist.device(),
+            Some(stylist),
+            Some(styles.primary()),
+            Some(pseudo),
+        )
+        .build()
+    }))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ComputedValues_Inherit(
+    raw_data: &PerDocumentStyleData,
+    pseudo: PseudoStyleType,
+    parent_style_context: Option<&ComputedValues>,
+    target: structs::InheritTarget,
+) -> Strong<ComputedValues> {
+    let data = raw_data.borrow();
+
+    let for_text = target == structs::InheritTarget::Text;
+    let pseudo = PseudoElement::from_pseudo_type(pseudo, None).unwrap();
+    debug_assert!(pseudo.is_anon_box());
+
+    let mut style = StyleBuilder::for_inheritance(
+        data.stylist.device(),
+        Some(&data.stylist),
+        parent_style_context,
+        Some(&pseudo),
+    );
+
+    if for_text {
+        StyleAdjuster::new(&mut style).adjust_for_text();
+    }
+
+    style.build().into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_SpecifiesAnimationsOrTransitions(
+    values: &ComputedValues,
+) -> bool {
+    let ui = values.get_ui();
+    ui.specifies_animations() || ui.specifies_transitions()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_GetStyleRuleList(
+    values: &ComputedValues,
+    rules: &mut ThinVec<*const LockedStyleRule>,
+) {
+    let rule_node = match values.rules {
+        Some(ref r) => r,
+        None => return,
+    };
+
+    for node in rule_node.self_and_ancestors() {
+        let style_rule = match node.style_source().and_then(|x| x.as_rule()) {
+            Some(rule) => rule,
+            _ => continue,
+        };
+
+        // For the rules with any important declaration, we insert them into
+        // rule tree twice, one for normal level and another for important
+        // level. So, we skip the important one to keep the specificity order of
+        // rules.
+        if node.importance().important() {
+            continue;
+        }
+
+        rules.push(&*style_rule);
+    }
+}
+
+/// println_stderr!() calls Gecko's printf_stderr(), which, unlike eprintln!(),
+/// will funnel output to Android logcat.
+#[cfg(feature = "gecko_debug")]
+macro_rules! println_stderr {
+    ($($e:expr),+) => {
+        {
+            let mut s = nsCString::new();
+            write!(s, $($e),+).unwrap();
+            s.write_char('\n').unwrap();
+            unsafe { bindings::Gecko_PrintfStderr(&s); }
+        }
+    }
+}
+
+#[cfg(feature = "gecko_debug")]
+fn dump_properties_and_rules(cv: &ComputedValues, properties: &LonghandIdSet) {
+    println_stderr!("  Properties:");
+    for p in properties.iter() {
+        let mut v = nsCString::new();
+        cv.computed_or_resolved_value(p, None, &mut v).unwrap();
+        println_stderr!("    {:?}: {}", p, v);
+    }
+    dump_rules(cv);
+}
+
+#[cfg(feature = "gecko_debug")]
+fn dump_rules(cv: &ComputedValues) {
+    println_stderr!("  Rules({:?}):", cv.pseudo());
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    if let Some(rules) = cv.rules.as_ref() {
+        for rn in rules.self_and_ancestors() {
+            if rn.importance().important() {
+                continue;
+            }
+            if let Some(d) = rn.style_source().and_then(|s| s.as_declarations()) {
+                println_stderr!("    [DeclarationBlock: {:?}]", d);
+            }
+            if let Some(r) = rn.style_source().and_then(|s| s.as_rule()) {
+                let mut s = nsCString::new();
+                r.read_with(&guard).to_css(&guard, &mut s).unwrap();
+                println_stderr!("    {}", s);
+            }
+        }
+    }
+}
+
+#[cfg(feature = "gecko_debug")]
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_EqualForCachedAnonymousContentStyle(
+    a: &ComputedValues,
+    b: &ComputedValues,
+) -> bool {
+    let mut differing_properties = a.differing_properties(b);
+
+    // Ignore any difference in -x-lang, which we can't override in the rules in scrollbars.css,
+    // but which makes no difference for the anonymous content subtrees we cache style for.
+    differing_properties.remove(LonghandId::XLang);
+    // Similarly, -x-lang can influence the font-family fallback we have for the initial
+    // font-family so remove it as well.
+    differing_properties.remove(LonghandId::FontFamily);
+    // We reset font-size to an explicit pixel value, and thus it can get affected by our inherited
+    // effective zoom. But we don't care about it for the same reason as above.
+    differing_properties.remove(LonghandId::FontSize);
+
+    // Ignore any difference in pref-controlled, inherited properties.  These properties may or may
+    // not be set by the 'all' declaration in scrollbars.css, depending on whether the pref was
+    // enabled at the time the UA sheets were parsed.
+    //
+    // If you add a new pref-controlled, inherited property, it must be defined with
+    // `has_effect_on_gecko_scrollbars=False` to declare that different values of this property on
+    // a <scrollbar> element or its descendant scrollbar part elements should have no effect on
+    // their rendering and behavior.
+    //
+    // If you do need a pref-controlled, inherited property to have an effect on these elements,
+    // then you will need to add some checks to the
+    // nsIAnonymousContentCreator::CreateAnonymousContent implementations of nsHTMLScrollFrame and
+    // nsScrollbarFrame to clear the AnonymousContentKey if a non-initial value is used.
+    differing_properties.remove_all(&LonghandIdSet::has_no_effect_on_gecko_scrollbars());
+
+    if !differing_properties.is_empty() {
+        println_stderr!("Actual style:");
+        dump_properties_and_rules(a, &differing_properties);
+        println_stderr!("Expected style:");
+        dump_properties_and_rules(b, &differing_properties);
+    }
+
+    differing_properties.is_empty()
+}
+
+#[cfg(feature = "gecko_debug")]
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_DumpMatchedRules(s: &ComputedValues) {
+    dump_rules(s);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ComputedValues_BlockifiedDisplay(
+    style: &ComputedValues,
+    is_root_element: bool,
+) -> u16 {
+    let display = style.get_box().clone_display();
+    let blockified_display = display.equivalent_block_display(is_root_element);
+    blockified_display.to_u16()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_Init(doc: &structs::Document) -> *mut PerDocumentStyleData {
+    let data = Box::new(PerDocumentStyleData::new(doc));
+
+    // Do this here rather than in Servo_Initialize since we need a document to
+    // get the default computed values from.
+    style::properties::generated::gecko::assert_initial_values_match(&data);
+
+    Box::into_raw(data) as *mut PerDocumentStyleData
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_Drop(data: *mut PerDocumentStyleData) {
+    let _ = Box::from_raw(data);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_RebuildCachedData(raw_data: &PerDocumentStyleData) {
+    let mut data = raw_data.borrow_mut();
+    data.stylist.device_mut().rebuild_cached_data();
+    data.undisplayed_style_cache.clear();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_CompatModeChanged(raw_data: &PerDocumentStyleData) {
+    let mut data = raw_data.borrow_mut();
+    let quirks_mode = data.stylist.device().document().mCompatMode;
+    data.stylist.set_quirks_mode(quirks_mode.into());
+}
+
+fn parse_property_into(
+    declarations: &mut SourcePropertyDeclaration,
+    property_id: PropertyId,
+    value: &nsACString,
+    origin: Origin,
+    url_data: &UrlExtraData,
+    parsing_mode: ParsingMode,
+    quirks_mode: QuirksMode,
+    rule_type: CssRuleType,
+    reporter: Option<&dyn ParseErrorReporter>,
+) -> Result<(), ()> {
+    let value = unsafe { value.as_str_unchecked() };
+
+    if let Some(non_custom) = property_id.non_custom_id() {
+        if !non_custom.allowed_in_rule(rule_type.into()) {
+            return Err(());
+        }
+    }
+
+    parse_one_declaration_into(
+        declarations,
+        property_id,
+        value,
+        origin,
+        url_data,
+        reporter,
+        parsing_mode,
+        quirks_mode,
+        rule_type,
+    )
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ParseProperty(
+    property: &structs::AnimatedPropertyID,
+    value: &nsACString,
+    data: *mut URLExtraData,
+    parsing_mode: ParsingMode,
+    quirks_mode: nsCompatibility,
+    loader: *mut Loader,
+    rule_type: CssRuleType,
+) -> Strong<LockedDeclarationBlock> {
+    let id = get_property_id_from_animatedpropertyid!(property, Strong::null());
+    let mut declarations = SourcePropertyDeclaration::default();
+    let reporter = ErrorReporter::new(ptr::null_mut(), loader, data);
+    let data = UrlExtraData::from_ptr_ref(&data);
+    let result = parse_property_into(
+        &mut declarations,
+        id,
+        value,
+        Origin::Author,
+        data,
+        parsing_mode,
+        quirks_mode.into(),
+        rule_type,
+        reporter.as_ref().map(|r| r as &dyn ParseErrorReporter),
+    );
+
+    match result {
+        Ok(()) => {
+            let global_style_data = &*GLOBAL_STYLE_DATA;
+            let mut block = PropertyDeclarationBlock::new();
+            block.extend(declarations.drain(), Importance::Normal);
+            Arc::new(global_style_data.shared_lock.wrap(block)).into()
+        },
+        Err(_) => Strong::null(),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ParseEasing(
+    easing: &nsACString,
+    output: &mut ComputedTimingFunction,
+) -> bool {
+    use style::properties::longhands::transition_timing_function;
+
+    let context = ParserContext::new(
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    let easing = easing.to_string();
+    let mut input = ParserInput::new(&easing);
+    let mut parser = Parser::new(&mut input);
+    let result =
+        parser.parse_entirely(|p| transition_timing_function::single_value::parse(&context, p));
+    match result {
+        Ok(parsed_easing) => {
+            *output = parsed_easing.to_computed_value_without_context();
+            true
+        },
+        Err(_) => false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_SerializeEasing(easing: &ComputedTimingFunction, output: &mut nsACString) {
+    easing.to_css(&mut CssWriter::new(output)).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetProperties_Overriding_Animation(
+    element: &RawGeckoElement,
+    list: &nsTArray<nsCSSPropertyID>,
+    set: &mut structs::nsCSSPropertyIDSet,
+) {
+    let element = GeckoElement(element);
+    let element_data = match element.borrow_data() {
+        Some(data) => data,
+        None => return,
+    };
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let guards = StylesheetGuards::same(&guard);
+    let (overridden, custom) = element_data
+        .styles
+        .primary()
+        .rules()
+        .get_properties_overriding_animations(&guards);
+    for p in list.iter() {
+        match NonCustomPropertyId::from_nscsspropertyid(*p) {
+            Some(property) => {
+                if let Some(id) = property.as_longhand() {
+                    if overridden.contains(id) {
+                        unsafe { Gecko_AddPropertyToSet(set, *p) };
+                    }
+                }
+            },
+            None => {
+                if *p == nsCSSPropertyID::eCSSPropertyExtra_variable && custom {
+                    unsafe { Gecko_AddPropertyToSet(set, *p) };
+                }
+            },
+        }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MatrixTransform_Operate(
+    matrix_operator: MatrixTransformOperator,
+    from: *const structs::Matrix4x4Components,
+    to: *const structs::Matrix4x4Components,
+    progress: f64,
+    output: *mut structs::Matrix4x4Components,
+) {
+    use self::MatrixTransformOperator::{Accumulate, Interpolate};
+    use style::values::computed::transform::Matrix3D;
+
+    let from = Matrix3D::from(unsafe { from.as_ref() }.expect("not a valid 'from' matrix"));
+    let to = Matrix3D::from(unsafe { to.as_ref() }.expect("not a valid 'to' matrix"));
+    let result = match matrix_operator {
+        Interpolate => from.animate(&to, Procedure::Interpolate { progress }),
+        Accumulate => from.animate(
+            &to,
+            Procedure::Accumulate {
+                count: progress as u64,
+            },
+        ),
+    };
+
+    let output = unsafe { output.as_mut() }.expect("not a valid 'output' matrix");
+    if let Ok(result) = result {
+        *output = result.into();
+    } else if progress < 0.5 {
+        *output = from.clone().into();
+    } else {
+        *output = to.clone().into();
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ParseStyleAttribute(
+    data: &nsACString,
+    raw_extra_data: *mut URLExtraData,
+    quirks_mode: nsCompatibility,
+    loader: *mut Loader,
+    rule_type: CssRuleType,
+) -> Strong<LockedDeclarationBlock> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let value = data.as_str_unchecked();
+    let reporter = ErrorReporter::new(ptr::null_mut(), loader, raw_extra_data);
+    let url_data = UrlExtraData::from_ptr_ref(&raw_extra_data);
+    Arc::new(global_style_data.shared_lock.wrap(parse_style_attribute(
+        value,
+        url_data,
+        reporter.as_ref().map(|r| r as &dyn ParseErrorReporter),
+        quirks_mode.into(),
+        rule_type,
+    )))
+    .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_CreateEmpty() -> Strong<LockedDeclarationBlock> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    Arc::new(
+        global_style_data
+            .shared_lock
+            .wrap(PropertyDeclarationBlock::new()),
+    )
+    .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_Clear(declarations: &LockedDeclarationBlock) {
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.clear();
+    });
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_Clone(
+    declarations: &LockedDeclarationBlock,
+) -> Strong<LockedDeclarationBlock> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    Arc::new(
+        global_style_data
+            .shared_lock
+            .wrap(declarations.read_with(&guard).clone()),
+    )
+    .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_Equals(
+    a: &LockedDeclarationBlock,
+    b: &LockedDeclarationBlock,
+) -> bool {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    a.read_with(&guard).declarations() == b.read_with(&guard).declarations()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_GetCssText(
+    declarations: &LockedDeclarationBlock,
+    result: &mut nsACString,
+) {
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.to_css(result).unwrap()
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SerializeOneValue(
+    decls: &LockedDeclarationBlock,
+    property_id: &structs::AnimatedPropertyID,
+    buffer: &mut nsACString,
+    computed_values: Option<&ComputedValues>,
+    data: &PerDocumentStyleData,
+) {
+    let property_id = get_property_id_from_animatedpropertyid!(property_id, ());
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let data = data.borrow();
+    let rv = decls.read_with(&guard).single_value_to_css(
+        &property_id,
+        buffer,
+        computed_values,
+        &data.stylist,
+    );
+    debug_assert!(rv.is_ok());
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SerializeFontValueForCanvas(
+    declarations: &LockedDeclarationBlock,
+    buffer: &mut nsACString,
+) {
+    use style::properties::shorthands::font;
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        let longhands = match font::LonghandsToSerialize::from_iter(decls.declarations().iter()) {
+            Ok(l) => l,
+            Err(()) => {
+                warn!("Unexpected property!");
+                return;
+            },
+        };
+
+        let rv = longhands.to_css(&mut CssWriter::new(buffer));
+        debug_assert!(rv.is_ok());
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_Count(declarations: &LockedDeclarationBlock) -> u32 {
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.declarations().len() as u32
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_GetNthProperty(
+    declarations: &LockedDeclarationBlock,
+    index: u32,
+    result: &mut nsACString,
+) -> bool {
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        if let Some(decl) = decls.declarations().get(index as usize) {
+            result.assign(&decl.id().name());
+            true
+        } else {
+            false
+        }
+    })
+}
+
+macro_rules! get_property_id_from_property {
+    ($property: ident, $ret: expr) => {{
+        let property = $property.as_str_unchecked();
+        match PropertyId::parse_enabled_for_all_content(property) {
+            Ok(property_id) => property_id,
+            Err(_) => return $ret,
+        }
+    }};
+}
+
+unsafe fn get_property_value(
+    declarations: &LockedDeclarationBlock,
+    property_id: PropertyId,
+    value: &mut nsACString,
+) {
+    // This callsite is hot enough that the lock acquisition shows up in profiles.
+    // Using an unchecked read here improves our performance by ~10% on the
+    // microbenchmark in bug 1355599.
+    read_locked_arc_unchecked(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.property_value_to_css(&property_id, value).unwrap();
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_GetPropertyValue(
+    declarations: &LockedDeclarationBlock,
+    property: &nsACString,
+    value: &mut nsACString,
+) {
+    get_property_value(
+        declarations,
+        get_property_id_from_property!(property, ()),
+        value,
+    )
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_GetPropertyValueById(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: &mut nsACString,
+) {
+    get_property_value(
+        declarations,
+        get_property_id_from_nscsspropertyid!(property, ()),
+        value,
+    )
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_GetPropertyIsImportant(
+    declarations: &LockedDeclarationBlock,
+    property: &nsACString,
+) -> bool {
+    let property_id = get_property_id_from_property!(property, false);
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.property_priority(&property_id).important()
+    })
+}
+
+#[inline(always)]
+fn set_property_to_declarations(
+    non_custom_property_id: Option<NonCustomPropertyId>,
+    block: &LockedDeclarationBlock,
+    parsed_declarations: &mut SourcePropertyDeclaration,
+    before_change_closure: DeclarationBlockMutationClosure,
+    importance: Importance,
+) -> bool {
+    let mut updates = Default::default();
+    let will_change = read_locked_arc(block, |decls: &PropertyDeclarationBlock| {
+        decls.prepare_for_update(&parsed_declarations, importance, &mut updates)
+    });
+    if !will_change {
+        return false;
+    }
+
+    before_change_closure.invoke(non_custom_property_id);
+    write_locked_arc(block, |decls: &mut PropertyDeclarationBlock| {
+        decls.update(parsed_declarations.drain(), importance, &mut updates)
+    });
+    true
+}
+
+fn set_property(
+    declarations: &LockedDeclarationBlock,
+    property_id: PropertyId,
+    value: &nsACString,
+    is_important: bool,
+    data: &UrlExtraData,
+    parsing_mode: ParsingMode,
+    quirks_mode: QuirksMode,
+    loader: *mut Loader,
+    rule_type: CssRuleType,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    let mut source_declarations = SourcePropertyDeclaration::default();
+    let reporter = ErrorReporter::new(ptr::null_mut(), loader, data.ptr());
+    let non_custom_property_id = property_id.non_custom_id();
+    let result = parse_property_into(
+        &mut source_declarations,
+        property_id,
+        value,
+        Origin::Author,
+        data,
+        parsing_mode,
+        quirks_mode,
+        rule_type,
+        reporter.as_ref().map(|r| r as &dyn ParseErrorReporter),
+    );
+
+    if result.is_err() {
+        return false;
+    }
+
+    let importance = if is_important {
+        Importance::Important
+    } else {
+        Importance::Normal
+    };
+
+    set_property_to_declarations(
+        non_custom_property_id,
+        declarations,
+        &mut source_declarations,
+        before_change_closure,
+        importance,
+    )
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SetProperty(
+    declarations: &LockedDeclarationBlock,
+    property: &nsACString,
+    value: &nsACString,
+    is_important: bool,
+    data: *mut URLExtraData,
+    parsing_mode: ParsingMode,
+    quirks_mode: nsCompatibility,
+    loader: *mut Loader,
+    rule_type: CssRuleType,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    set_property(
+        declarations,
+        get_property_id_from_property!(property, false),
+        value,
+        is_important,
+        UrlExtraData::from_ptr_ref(&data),
+        parsing_mode,
+        quirks_mode.into(),
+        loader,
+        rule_type,
+        before_change_closure,
+    )
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SetPropertyToAnimationValue(
+    declarations: &LockedDeclarationBlock,
+    animation_value: &AnimationValue,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    let non_custom_property_id = match animation_value.id() {
+        PropertyDeclarationId::Longhand(id) => Some(id.into()),
+        PropertyDeclarationId::Custom(_) => None,
+    };
+    let mut source_declarations = SourcePropertyDeclaration::with_one(animation_value.uncompute());
+
+    set_property_to_declarations(
+        non_custom_property_id,
+        declarations,
+        &mut source_declarations,
+        before_change_closure,
+        Importance::Normal,
+    )
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SetPropertyById(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: &nsACString,
+    is_important: bool,
+    data: *mut URLExtraData,
+    parsing_mode: ParsingMode,
+    quirks_mode: nsCompatibility,
+    loader: *mut Loader,
+    rule_type: CssRuleType,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    set_property(
+        declarations,
+        get_property_id_from_nscsspropertyid!(property, false),
+        value,
+        is_important,
+        UrlExtraData::from_ptr_ref(&data),
+        parsing_mode,
+        quirks_mode.into(),
+        loader,
+        rule_type,
+        before_change_closure,
+    )
+}
+
+fn remove_property(
+    declarations: &LockedDeclarationBlock,
+    property_id: PropertyId,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    let first_declaration = read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.first_declaration_to_remove(&property_id)
+    });
+
+    let first_declaration = match first_declaration {
+        Some(i) => i,
+        None => return false,
+    };
+
+    before_change_closure.invoke(property_id.non_custom_id());
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.remove_property(&property_id, first_declaration)
+    });
+
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_RemoveProperty(
+    declarations: &LockedDeclarationBlock,
+    property: &nsACString,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    remove_property(
+        declarations,
+        get_property_id_from_property!(property, false),
+        before_change_closure,
+    )
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_RemovePropertyById(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    before_change_closure: DeclarationBlockMutationClosure,
+) -> bool {
+    remove_property(
+        declarations,
+        get_property_id_from_nscsspropertyid!(property, false),
+        before_change_closure,
+    )
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_Create() -> Strong<LockedMediaList> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    Arc::new(global_style_data.shared_lock.wrap(MediaList::empty())).into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_DeepClone(list: &LockedMediaList) -> Strong<LockedMediaList> {
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    read_locked_arc(list, |list: &MediaList| {
+        Arc::new(global_style_data.shared_lock.wrap(list.clone())).into()
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_Matches(
+    list: &LockedMediaList,
+    raw_data: &PerDocumentStyleData,
+) -> bool {
+    let per_doc_data = raw_data.borrow();
+    read_locked_arc(list, |list: &MediaList| {
+        list.evaluate(
+            per_doc_data.stylist.device(),
+            per_doc_data.stylist.quirks_mode(),
+        )
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_HasCSSWideKeyword(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+) -> bool {
+    let property_id = get_property_id_from_nscsspropertyid!(property, false);
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.has_css_wide_keyword(&property_id)
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_GetText(list: &LockedMediaList, result: &mut nsACString) {
+    read_locked_arc(list, |list: &MediaList| {
+        list.to_css(&mut CssWriter::new(result)).unwrap();
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_MediaList_SetText(
+    list: &LockedMediaList,
+    text: &nsACString,
+    caller_type: CallerType,
+) {
+    let text = text.as_str_unchecked();
+
+    let mut input = ParserInput::new(&text);
+    let mut parser = Parser::new(&mut input);
+    let url_data = dummy_url_data();
+
+    // TODO(emilio): If the need for `CallerType` appears in more places,
+    // consider adding an explicit member in `ParserContext` instead of doing
+    // this (or adding a dummy "chrome://" url data).
+    //
+    // For media query parsing it's effectively the same, so for now...
+    let origin = match caller_type {
+        CallerType::System => Origin::UserAgent,
+        CallerType::NonSystem => Origin::Author,
+    };
+
+    let context = ParserContext::new(
+        origin,
+        url_data,
+        Some(CssRuleType::Media),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        // TODO(emilio): Looks like error reporting could be useful here?
+        None,
+        None,
+    );
+
+    write_locked_arc(list, |list: &mut MediaList| {
+        *list = MediaList::parse(&context, &mut parser);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_IsViewportDependent(list: &LockedMediaList) -> bool {
+    read_locked_arc(list, |list: &MediaList| list.is_viewport_dependent())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_GetLength(list: &LockedMediaList) -> u32 {
+    read_locked_arc(list, |list: &MediaList| list.media_queries.len() as u32)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_GetMediumAt(
+    list: &LockedMediaList,
+    index: u32,
+    result: &mut nsACString,
+) -> bool {
+    read_locked_arc(list, |list: &MediaList| {
+        let media_query = match list.media_queries.get(index as usize) {
+            Some(mq) => mq,
+            None => return false,
+        };
+        media_query.to_css(&mut CssWriter::new(result)).unwrap();
+        true
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_AppendMedium(list: &LockedMediaList, new_medium: &nsACString) {
+    let new_medium = unsafe { new_medium.as_str_unchecked() };
+    let url_data = unsafe { dummy_url_data() };
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        Some(CssRuleType::Media),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    write_locked_arc(list, |list: &mut MediaList| {
+        list.append_medium(&context, new_medium);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_DeleteMedium(
+    list: &LockedMediaList,
+    old_medium: &nsACString,
+) -> bool {
+    let old_medium = unsafe { old_medium.as_str_unchecked() };
+    let url_data = unsafe { dummy_url_data() };
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        Some(CssRuleType::Media),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    write_locked_arc(list, |list: &mut MediaList| {
+        list.delete_medium(&context, old_medium)
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_MediaList_SizeOfIncludingThis(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    list: &LockedMediaList,
+) -> usize {
+    use malloc_size_of::MallocSizeOf;
+    use malloc_size_of::MallocUnconditionalShallowSizeOf;
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    let mut ops = MallocSizeOfOps::new(
+        malloc_size_of.unwrap(),
+        Some(malloc_enclosing_size_of.unwrap()),
+        None,
+    );
+
+    unsafe { ArcBorrow::from_ref(list) }.with_arc(|list| {
+        let mut n = 0;
+        n += list.unconditional_shallow_size_of(&mut ops);
+        n += list.read_with(&guard).size_of(&mut ops);
+        n
+    })
+}
+
+macro_rules! get_longhand_from_id {
+    ($id:expr) => {
+        match LonghandId::from_nscsspropertyid($id) {
+            Some(lh) => lh,
+            _ => panic!("stylo: unknown presentation property with id"),
+        }
+    };
+}
+
+macro_rules! match_wrap_declared {
+    ($longhand:ident, $($property:ident => $inner:expr,)*) => (
+        match $longhand {
+            $(
+                LonghandId::$property => PropertyDeclaration::$property($inner),
+            )*
+            _ => {
+                panic!("stylo: Don't know how to handle presentation property");
+            }
+        }
+    )
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_PropertyIsSet(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+) -> bool {
+    read_locked_arc(declarations, |decls: &PropertyDeclarationBlock| {
+        decls.contains(PropertyDeclarationId::Longhand(get_longhand_from_id!(
+            property
+        )))
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SetIdentStringValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: *mut nsAtom,
+) {
+    use style::properties::longhands::_x_lang::computed_value::T as Lang;
+    use style::properties::PropertyDeclaration;
+
+    let long = get_longhand_from_id!(property);
+    let prop = match_wrap_declared! { long,
+        XLang => Lang(Atom::from_raw(value)),
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+#[allow(unreachable_code)]
+pub extern "C" fn Servo_DeclarationBlock_SetKeywordValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: i32,
+) {
+    use num_traits::FromPrimitive;
+    use style::properties::longhands;
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::box_::{VerticalAlign, VerticalAlignKeyword};
+    use style::values::generics::font::FontStyle;
+    use style::values::specified::{
+        table::CaptionSide, BorderStyle, Clear, Display, Float, TextAlign, TextEmphasisPosition,
+        TextTransform,
+    };
+
+    fn get_from_computed<T>(value: u32) -> T
+    where
+        T: ToComputedValue,
+        T::ComputedValue: FromPrimitive,
+    {
+        T::from_computed_value(&T::ComputedValue::from_u32(value).unwrap())
+    }
+
+    let long = get_longhand_from_id!(property);
+    let value = value as u32;
+
+    let prop = match_wrap_declared! { long,
+        MozUserModify => longhands::_moz_user_modify::SpecifiedValue::from_gecko_keyword(value),
+        Direction => get_from_computed::<longhands::direction::SpecifiedValue>(value),
+        Display => get_from_computed::<Display>(value),
+        Float => get_from_computed::<Float>(value),
+        Clear => get_from_computed::<Clear>(value),
+        VerticalAlign => VerticalAlign::Keyword(VerticalAlignKeyword::from_u32(value).unwrap()),
+        TextAlign => get_from_computed::<TextAlign>(value),
+        TextEmphasisPosition => TextEmphasisPosition::from_bits_retain(value as u8),
+        FontSize => {
+            // We rely on Gecko passing in font-size values (0...7) here.
+            longhands::font_size::SpecifiedValue::from_html_size(value as u8)
+        },
+        FontStyle => {
+            style::values::specified::FontStyle::Specified(if value == structs::NS_FONT_STYLE_ITALIC {
+                FontStyle::Italic
+            } else {
+                debug_assert_eq!(value, structs::NS_FONT_STYLE_NORMAL);
+                FontStyle::Normal
+            })
+        },
+        FontWeight => longhands::font_weight::SpecifiedValue::from_gecko_keyword(value),
+        ListStyleType => Box::new(longhands::list_style_type::SpecifiedValue::from_gecko_keyword(value)),
+        MathStyle => longhands::math_style::SpecifiedValue::from_gecko_keyword(value),
+        MozMathVariant => longhands::_moz_math_variant::SpecifiedValue::from_gecko_keyword(value),
+        WhiteSpaceCollapse => get_from_computed::<longhands::white_space_collapse::SpecifiedValue>(value),
+        TextWrapMode => get_from_computed::<longhands::text_wrap_mode::SpecifiedValue>(value),
+        CaptionSide => get_from_computed::<CaptionSide>(value),
+        BorderTopStyle => get_from_computed::<BorderStyle>(value),
+        BorderRightStyle => get_from_computed::<BorderStyle>(value),
+        BorderBottomStyle => get_from_computed::<BorderStyle>(value),
+        BorderLeftStyle => get_from_computed::<BorderStyle>(value),
+        TextTransform => {
+            debug_assert_eq!(value, structs::StyleTextTransformCase_None as u32);
+            TextTransform::none()
+        },
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetIntValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: i32,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::specified::Integer;
+
+    let long = get_longhand_from_id!(property);
+    let prop = match_wrap_declared! { long,
+        XSpan => Integer::new(value),
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetMathDepthValue(
+    declarations: &LockedDeclarationBlock,
+    value: i32,
+    is_relative: bool,
+) {
+    use style::properties::longhands::math_depth::SpecifiedValue as MathDepth;
+    use style::properties::PropertyDeclaration;
+
+    let integer_value = style::values::specified::Integer::new(value);
+    let prop = PropertyDeclaration::MathDepth(if is_relative {
+        MathDepth::Add(integer_value)
+    } else {
+        MathDepth::Absolute(integer_value)
+    });
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetCounterResetListItem(
+    declarations: &LockedDeclarationBlock,
+    counter_value: i32,
+    is_reversed: bool,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::counters::{CounterPair, CounterReset};
+
+    let prop = PropertyDeclaration::CounterReset(CounterReset::new(vec![CounterPair {
+        name: CustomIdent(atom!("list-item")),
+        value: style::values::specified::Integer::new(counter_value),
+        is_reversed,
+    }]));
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetCounterSetListItem(
+    declarations: &LockedDeclarationBlock,
+    counter_value: i32,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::counters::{CounterPair, CounterSet};
+
+    let prop = PropertyDeclaration::CounterSet(CounterSet::new(vec![CounterPair {
+        name: CustomIdent(atom!("list-item")),
+        value: style::values::specified::Integer::new(counter_value),
+        is_reversed: false,
+    }]));
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetPixelValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: f32,
+) {
+    use style::properties::longhands::border_spacing::SpecifiedValue as BorderSpacing;
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::length::{LengthPercentageOrAuto, Size};
+    use style::values::generics::NonNegative;
+    use style::values::specified::length::{
+        LengthPercentage, NonNegativeLength, NonNegativeLengthPercentage,
+    };
+    use style::values::specified::{BorderCornerRadius, BorderSideWidth};
+
+    let long = get_longhand_from_id!(property);
+    let nocalc = NoCalcLength::from_px(value);
+    let lp = LengthPercentage::Length(nocalc);
+    let lp_or_auto = LengthPercentageOrAuto::LengthPercentage(lp.clone());
+    let prop = match_wrap_declared! { long,
+        Height => Size::LengthPercentage(NonNegative(lp)),
+        Width => Size::LengthPercentage(NonNegative(lp)),
+        BorderTopWidth => BorderSideWidth::from_px(value),
+        BorderRightWidth => BorderSideWidth::from_px(value),
+        BorderBottomWidth => BorderSideWidth::from_px(value),
+        BorderLeftWidth => BorderSideWidth::from_px(value),
+        MarginTop => lp_or_auto,
+        MarginRight => lp_or_auto,
+        MarginBottom => lp_or_auto,
+        MarginLeft => lp_or_auto,
+        PaddingTop => NonNegative(lp),
+        PaddingRight => NonNegative(lp),
+        PaddingBottom => NonNegative(lp),
+        PaddingLeft => NonNegative(lp),
+        BorderSpacing => {
+            let v = NonNegativeLength::from(nocalc);
+            Box::new(BorderSpacing::new(v.clone(), v))
+        },
+        BorderTopLeftRadius => {
+            let length = NonNegativeLengthPercentage::from(nocalc);
+            Box::new(BorderCornerRadius::new(length.clone(), length))
+        },
+        BorderTopRightRadius => {
+            let length = NonNegativeLengthPercentage::from(nocalc);
+            Box::new(BorderCornerRadius::new(length.clone(), length))
+        },
+        BorderBottomLeftRadius => {
+            let length = NonNegativeLengthPercentage::from(nocalc);
+            Box::new(BorderCornerRadius::new(length.clone(), length))
+        },
+        BorderBottomRightRadius => {
+            let length = NonNegativeLengthPercentage::from(nocalc);
+            Box::new(BorderCornerRadius::new(length.clone(), length))
+        },
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetLengthValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: f32,
+    unit: structs::nsCSSUnit,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::length::{LengthPercentageOrAuto, Size};
+    use style::values::generics::NonNegative;
+    use style::values::specified::length::{
+        FontRelativeLength, LengthPercentage, ViewportPercentageLength,
+    };
+    use style::values::specified::FontSize;
+
+    let long = get_longhand_from_id!(property);
+    let nocalc = match unit {
+        structs::nsCSSUnit::eCSSUnit_EM => {
+            NoCalcLength::FontRelative(FontRelativeLength::Em(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_XHeight => {
+            NoCalcLength::FontRelative(FontRelativeLength::Ex(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_RootEM => {
+            NoCalcLength::FontRelative(FontRelativeLength::Rem(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_Char => {
+            NoCalcLength::FontRelative(FontRelativeLength::Ch(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_Ideographic => {
+            NoCalcLength::FontRelative(FontRelativeLength::Ic(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_CapHeight => {
+            NoCalcLength::FontRelative(FontRelativeLength::Cap(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_Pixel => NoCalcLength::Absolute(AbsoluteLength::Px(value)),
+        structs::nsCSSUnit::eCSSUnit_Inch => NoCalcLength::Absolute(AbsoluteLength::In(value)),
+        structs::nsCSSUnit::eCSSUnit_Centimeter => {
+            NoCalcLength::Absolute(AbsoluteLength::Cm(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_Millimeter => {
+            NoCalcLength::Absolute(AbsoluteLength::Mm(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_Point => NoCalcLength::Absolute(AbsoluteLength::Pt(value)),
+        structs::nsCSSUnit::eCSSUnit_Pica => NoCalcLength::Absolute(AbsoluteLength::Pc(value)),
+        structs::nsCSSUnit::eCSSUnit_Quarter => NoCalcLength::Absolute(AbsoluteLength::Q(value)),
+        structs::nsCSSUnit::eCSSUnit_VW => {
+            NoCalcLength::ViewportPercentage(ViewportPercentageLength::Vw(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_VH => {
+            NoCalcLength::ViewportPercentage(ViewportPercentageLength::Vh(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_VMin => {
+            NoCalcLength::ViewportPercentage(ViewportPercentageLength::Vmin(value))
+        },
+        structs::nsCSSUnit::eCSSUnit_VMax => {
+            NoCalcLength::ViewportPercentage(ViewportPercentageLength::Vmax(value))
+        },
+        _ => unreachable!("Unknown unit passed to SetLengthValue"),
+    };
+
+    let prop = match_wrap_declared! { long,
+        Width => Size::LengthPercentage(NonNegative(LengthPercentage::Length(nocalc))),
+        Height => Size::LengthPercentage(NonNegative(LengthPercentage::Length(nocalc))),
+        X =>  LengthPercentage::Length(nocalc),
+        Y =>  LengthPercentage::Length(nocalc),
+        Cx => LengthPercentage::Length(nocalc),
+        Cy => LengthPercentage::Length(nocalc),
+        R =>  NonNegative(LengthPercentage::Length(nocalc)),
+        Rx => LengthPercentageOrAuto::LengthPercentage(NonNegative(LengthPercentage::Length(nocalc))),
+        Ry => LengthPercentageOrAuto::LengthPercentage(NonNegative(LengthPercentage::Length(nocalc))),
+        FontSize => FontSize::Length(LengthPercentage::Length(nocalc)),
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetPathValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    path: &nsTArray<f32>,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::specified::DProperty;
+
+    // 1. Decode the path data from SVG.
+    let path = match specified::SVGPathData::decode_from_f32_array(path) {
+        Ok(p) => p,
+        Err(()) => return,
+    };
+
+    // 2. Set decoded path into style.
+    let long = get_longhand_from_id!(property);
+    let prop = match_wrap_declared! { long,
+        D => if path.0.is_empty() { DProperty::None } else { DProperty::Path(path) },
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetPercentValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: f32,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::computed::Percentage;
+    use style::values::generics::length::{LengthPercentageOrAuto, Size};
+    use style::values::generics::NonNegative;
+    use style::values::specified::length::LengthPercentage;
+    use style::values::specified::FontSize;
+
+    let long = get_longhand_from_id!(property);
+    let pc = Percentage(value);
+    let lp = LengthPercentage::Percentage(pc);
+    let lp_or_auto = LengthPercentageOrAuto::LengthPercentage(lp.clone());
+
+    let prop = match_wrap_declared! { long,
+        Height => Size::LengthPercentage(NonNegative(lp)),
+        Width => Size::LengthPercentage(NonNegative(lp)),
+        X =>  lp,
+        Y =>  lp,
+        Cx => lp,
+        Cy => lp,
+        R =>  NonNegative(lp),
+        Rx => LengthPercentageOrAuto::LengthPercentage(NonNegative(lp)),
+        Ry => LengthPercentageOrAuto::LengthPercentage(NonNegative(lp)),
+        MarginTop => lp_or_auto,
+        MarginRight => lp_or_auto,
+        MarginBottom => lp_or_auto,
+        MarginLeft => lp_or_auto,
+        FontSize => FontSize::Length(LengthPercentage::Percentage(pc)),
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetAutoValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::length::{LengthPercentageOrAuto, Size};
+
+    let long = get_longhand_from_id!(property);
+    let auto = LengthPercentageOrAuto::Auto;
+
+    let prop = match_wrap_declared! { long,
+        Height => Size::auto(),
+        Width => Size::auto(),
+        MarginTop => auto,
+        MarginRight => auto,
+        MarginBottom => auto,
+        MarginLeft => auto,
+        AspectRatio => specified::AspectRatio::auto(),
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetCurrentColor(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::specified::Color;
+
+    let long = get_longhand_from_id!(property);
+    let cc = Color::currentcolor();
+
+    let prop = match_wrap_declared! { long,
+        BorderTopColor => cc,
+        BorderRightColor => cc,
+        BorderBottomColor => cc,
+        BorderLeftColor => cc,
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetColorValue(
+    declarations: &LockedDeclarationBlock,
+    property: nsCSSPropertyID,
+    value: structs::nscolor,
+) {
+    use style::gecko::values::convert_nscolor_to_absolute_color;
+    use style::properties::longhands;
+    use style::properties::PropertyDeclaration;
+    use style::values::specified::Color;
+
+    let long = get_longhand_from_id!(property);
+    let rgba = convert_nscolor_to_absolute_color(value);
+    let color = Color::from_absolute_color(rgba);
+
+    let prop = match_wrap_declared! { long,
+        BorderTopColor => color,
+        BorderRightColor => color,
+        BorderBottomColor => color,
+        BorderLeftColor => color,
+        Color => longhands::color::SpecifiedValue(color),
+        BackgroundColor => color,
+    };
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(prop, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SetFontFamily(
+    declarations: &LockedDeclarationBlock,
+    value: &nsACString,
+) {
+    use style::properties::longhands::font_family::SpecifiedValue as FontFamily;
+    use style::properties::PropertyDeclaration;
+
+    let string = value.as_str_unchecked();
+    let mut input = ParserInput::new(&string);
+    let mut parser = Parser::new(&mut input);
+    let context = ParserContext::new(
+        Origin::Author,
+        dummy_url_data(),
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    let result = FontFamily::parse(&context, &mut parser);
+    if let Ok(family) = result {
+        if parser.is_exhausted() {
+            let decl = PropertyDeclaration::FontFamily(family);
+            write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+                decls.push(decl, Importance::Normal);
+            })
+        }
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_DeclarationBlock_SetBackgroundImage(
+    declarations: &LockedDeclarationBlock,
+    value: &nsACString,
+    raw_extra_data: *mut URLExtraData,
+) {
+    use style::properties::longhands::background_image::SpecifiedValue as BackgroundImage;
+    use style::properties::PropertyDeclaration;
+    use style::stylesheets::CorsMode;
+    use style::values::generics::image::Image;
+    use style::values::specified::url::SpecifiedImageUrl;
+
+    let url_data = UrlExtraData::from_ptr_ref(&raw_extra_data);
+    let string = value.as_str_unchecked();
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    let url = SpecifiedImageUrl::parse_from_string(string.into(), &context, CorsMode::None);
+    let decl = PropertyDeclaration::BackgroundImage(BackgroundImage(vec![Image::Url(url)].into()));
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(decl, Importance::Normal);
+    });
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetTextDecorationColorOverride(
+    declarations: &LockedDeclarationBlock,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::specified::text::TextDecorationLine;
+
+    let decoration = TextDecorationLine::COLOR_OVERRIDE;
+    let decl = PropertyDeclaration::TextDecorationLine(decoration);
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(decl, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_DeclarationBlock_SetAspectRatio(
+    declarations: &LockedDeclarationBlock,
+    width: f32,
+    height: f32,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::values::generics::position::AspectRatio;
+
+    let decl = PropertyDeclaration::AspectRatio(AspectRatio::from_mapped_ratio(width, height));
+    write_locked_arc(declarations, |decls: &mut PropertyDeclarationBlock| {
+        decls.push(decl, Importance::Normal);
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CSSSupports2(property: &nsACString, value: &nsACString) -> bool {
+    let id = unsafe { get_property_id_from_property!(property, false) };
+
+    let mut declarations = SourcePropertyDeclaration::default();
+    parse_property_into(
+        &mut declarations,
+        id,
+        value,
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        CssRuleType::Style,
+        None,
+    )
+    .is_ok()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CSSSupports(
+    cond: &nsACString,
+    ua_origin: bool,
+    chrome_sheet: bool,
+    quirks: bool,
+) -> bool {
+    let condition = unsafe { cond.as_str_unchecked() };
+    let mut input = ParserInput::new(&condition);
+    let mut input = Parser::new(&mut input);
+    let cond = match input.parse_entirely(parse_condition_or_declaration) {
+        Ok(c) => c,
+        Err(..) => return false,
+    };
+
+    let origin = if ua_origin {
+        Origin::UserAgent
+    } else {
+        Origin::Author
+    };
+    let url_data = unsafe {
+        UrlExtraData::from_ptr_ref(if chrome_sheet {
+            &DUMMY_CHROME_URL_DATA
+        } else {
+            &DUMMY_URL_DATA
+        })
+    };
+    let quirks_mode = if quirks {
+        QuirksMode::Quirks
+    } else {
+        QuirksMode::NoQuirks
+    };
+
+    // NOTE(emilio): The supports API is not associated to any stylesheet,
+    // so the fact that there is no namespace map here is fine.
+    let context = ParserContext::new(
+        origin,
+        url_data,
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        quirks_mode,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    cond.eval(&context)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CSSSupportsForImport(after_rule: &nsACString) -> bool {
+    let condition = unsafe { after_rule.as_str_unchecked() };
+    let mut input = ParserInput::new(&condition);
+    let mut input = Parser::new(&mut input);
+
+    // NOTE(emilio): The supports API is not associated to any stylesheet,
+    // so the fact that there is no namespace map here is fine.
+    let mut context = ParserContext::new(
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    let (_layer, supports) = ImportRule::parse_layer_and_supports(&mut input, &mut context);
+
+    supports.map_or(true, |s| s.enabled)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_NoteExplicitHints(
+    element: &RawGeckoElement,
+    restyle_hint: RestyleHint,
+    change_hint: nsChangeHint,
+) {
+    GeckoElement(element).note_explicit_hints(restyle_hint, change_hint);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_TakeChangeHint(element: &RawGeckoElement, was_restyled: &mut bool) -> u32 {
+    let element = GeckoElement(element);
+
+    let damage = match element.mutate_data() {
+        Some(mut data) => {
+            *was_restyled = data.is_restyle();
+
+            let damage = data.damage;
+            data.clear_restyle_state();
+            damage
+        },
+        None => {
+            warn!("Trying to get change hint from unstyled element");
+            *was_restyled = false;
+            GeckoRestyleDamage::empty()
+        },
+    };
+
+    debug!("Servo_TakeChangeHint: {:?}, damage={:?}", element, damage);
+    // We'd like to return `nsChangeHint` here, but bindgen bitfield enums don't
+    // work as return values with the Linux 32-bit ABI at the moment because
+    // they wrap the value in a struct, so for now just unwrap it.
+    damage.as_change_hint().0
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ResolveStyle(element: &RawGeckoElement) -> Strong<ComputedValues> {
+    let element = GeckoElement(element);
+    debug!("Servo_ResolveStyle: {:?}", element);
+    let data = element
+        .borrow_data()
+        .expect("Resolving style on unstyled element");
+
+    debug_assert!(
+        element.has_current_styles(&*data),
+        "Resolving style on {:?} without current styles: {:?}",
+        element,
+        data
+    );
+    data.styles.primary().clone().into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ResolveStyleLazily(
+    element: &RawGeckoElement,
+    pseudo_type: PseudoStyleType,
+    functional_pseudo_parameter: *mut nsAtom,
+    rule_inclusion: StyleRuleInclusion,
+    snapshots: *const ServoElementSnapshotTable,
+    cache_generation: u64,
+    can_use_cache: bool,
+    raw_data: &PerDocumentStyleData,
+) -> Strong<ComputedValues> {
+    debug_assert!(!snapshots.is_null());
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let element = GeckoElement(element);
+    let mut data = raw_data.borrow_mut();
+    let data = &mut *data;
+    let rule_inclusion = RuleInclusion::from(rule_inclusion);
+    let pseudo_element = PseudoElement::from_pseudo_type(
+        pseudo_type,
+        get_functional_pseudo_parameter_atom(functional_pseudo_parameter),
+    );
+
+    let matching_fn = |pseudo: &PseudoElement| match pseudo_element {
+        Some(ref p) => *pseudo == *p,
+        _ => false,
+    };
+
+    if cache_generation != data.undisplayed_style_cache_generation {
+        data.undisplayed_style_cache.clear();
+        data.undisplayed_style_cache_generation = cache_generation;
+    }
+
+    let stylist = &data.stylist;
+    let finish = |styles: &ElementStyles, is_probe: bool| -> Option<Arc<ComputedValues>> {
+        match pseudo_element {
+            Some(ref pseudo) => {
+                get_pseudo_style(
+                    &guard,
+                    element,
+                    pseudo,
+                    rule_inclusion,
+                    styles,
+                    /* inherited_styles = */ None,
+                    &stylist,
+                    is_probe,
+                    if pseudo.is_highlight() {
+                        Some(&matching_fn)
+                    } else {
+                        None
+                    },
+                )
+            },
+            None => Some(styles.primary().clone()),
+        }
+    };
+
+    let is_before_or_after = pseudo_element
+        .as_ref()
+        .map_or(false, |p| p.is_before_or_after());
+
+    // In the common case we already have the style. Check that before setting
+    // up all the computation machinery.
+    //
+    // Also, only probe in the ::before or ::after case, since their styles may
+    // not be in the `ElementData`, given they may exist but not be applicable
+    // to generate an actual pseudo-element (like, having a `content: none`).
+    if rule_inclusion == RuleInclusion::All {
+        let styles = element.borrow_data().and_then(|d| {
+            if d.has_styles() {
+                finish(&d.styles, is_before_or_after)
+            } else {
+                None
+            }
+        });
+        if let Some(result) = styles {
+            return result.into();
+        }
+        if pseudo_element.is_none() && can_use_cache {
+            if let Some(style) = data.undisplayed_style_cache.get(&element.opaque()) {
+                return style.clone().into();
+            }
+        }
+    }
+
+    // We don't have the style ready. Go ahead and compute it as necessary.
+    let shared = create_shared_context(
+        &global_style_data,
+        &guard,
+        &stylist,
+        TraversalFlags::empty(),
+        unsafe { &*snapshots },
+    );
+    let mut tlc = ThreadLocalStyleContext::new();
+    let mut context = StyleContext {
+        shared: &shared,
+        thread_local: &mut tlc,
+    };
+
+    let styles = resolve_style(
+        &mut context,
+        element,
+        rule_inclusion,
+        pseudo_element.as_ref(),
+        if can_use_cache {
+            Some(&mut data.undisplayed_style_cache)
+        } else {
+            None
+        },
+    );
+
+    finish(&styles, /* is_probe = */ false)
+        .expect("We're not probing, so we should always get a style back")
+        .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ReparentStyle(
+    style_to_reparent: &ComputedValues,
+    parent_style: &ComputedValues,
+    layout_parent_style: &ComputedValues,
+    element: Option<&RawGeckoElement>,
+    raw_data: &PerDocumentStyleData,
+) -> Strong<ComputedValues> {
+    use style::properties::FirstLineReparenting;
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let doc_data = raw_data.borrow();
+    let inputs = CascadeInputs::new_from_style(style_to_reparent);
+    let pseudo = style_to_reparent.pseudo();
+    let element = element.map(GeckoElement);
+
+    doc_data
+        .stylist
+        .cascade_style_and_visited(
+            element,
+            pseudo.as_ref(),
+            inputs,
+            &StylesheetGuards::same(&guard),
+            Some(parent_style),
+            Some(layout_parent_style),
+            FirstLineReparenting::Yes { style_to_reparent },
+            /* rule_cache = */ None,
+            &mut RuleCacheConditions::default(),
+        )
+        .into()
+}
+
+#[cfg(feature = "gecko_debug")]
+fn simulate_compute_values_failure(property: &PropertyValuePair) -> bool {
+    let p = &property.mProperty;
+    let id = get_property_id_from_animatedpropertyid!(p, false);
+    id.as_shorthand().is_ok() && property.mSimulateComputeValuesFailure
+}
+
+#[cfg(not(feature = "gecko_debug"))]
+fn simulate_compute_values_failure(_: &PropertyValuePair) -> bool {
+    false
+}
+
+fn create_context_for_animation<'a>(
+    per_doc_data: &'a PerDocumentStyleDataImpl,
+    style: &'a ComputedValues,
+    parent_style: Option<&'a ComputedValues>,
+    for_smil_animation: bool,
+    rule_cache_conditions: &'a mut RuleCacheConditions,
+    container_size_query: ContainerSizeQuery<'a>,
+) -> Context<'a> {
+    Context::new_for_animation(
+        StyleBuilder::for_animation(
+            per_doc_data.stylist.device(),
+            Some(&per_doc_data.stylist),
+            style,
+            parent_style,
+        ),
+        for_smil_animation,
+        per_doc_data.stylist.quirks_mode(),
+        rule_cache_conditions,
+        container_size_query,
+    )
+}
+
+struct PropertyAndIndex {
+    property: PropertyId,
+    index: usize,
+}
+
+struct PrioritizedPropertyIter<'a> {
+    properties: &'a [PropertyValuePair],
+    sorted_property_indices: Vec<PropertyAndIndex>,
+    curr: usize,
+}
+
+impl<'a> PrioritizedPropertyIter<'a> {
+    fn new(properties: &'a [PropertyValuePair]) -> PrioritizedPropertyIter {
+        use style::values::animated::compare_property_priority;
+
+        // If we fail to convert a nsCSSPropertyID into a PropertyId we
+        // shouldn't fail outright but instead by treating that property as the
+        // 'all' property we make it sort last.
+        let mut sorted_property_indices: Vec<PropertyAndIndex> = properties
+            .iter()
+            .enumerate()
+            .map(|(index, pair)| {
+                let property = PropertyId::from_gecko_animated_property_id(&pair.mProperty)
+                    .unwrap_or(PropertyId::NonCustom(ShorthandId::All.into()));
+                PropertyAndIndex { property, index }
+            })
+            .collect();
+        sorted_property_indices.sort_by(|a, b| compare_property_priority(&a.property, &b.property));
+
+        PrioritizedPropertyIter {
+            properties,
+            sorted_property_indices,
+            curr: 0,
+        }
+    }
+
+    fn reset(&mut self) {
+        self.curr = 0;
+    }
+}
+
+impl<'a> Iterator for PrioritizedPropertyIter<'a> {
+    type Item = &'a PropertyValuePair;
+
+    fn next(&mut self) -> Option<&'a PropertyValuePair> {
+        if self.curr >= self.sorted_property_indices.len() {
+            return None;
+        }
+        self.curr += 1;
+        Some(&self.properties[self.sorted_property_indices[self.curr - 1].index])
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetComputedKeyframeValues(
+    keyframes: &nsTArray<structs::Keyframe>,
+    element: &RawGeckoElement,
+    pseudo_type: PseudoStyleType,
+    style: &ComputedValues,
+    raw_data: &PerDocumentStyleData,
+    computed_keyframes: &mut nsTArray<structs::ComputedKeyframeValues>,
+) {
+    use style::properties::PropertyDeclaration;
+    use style::custom_properties::CustomPropertiesBuilder;
+    use style::applicable_declarations::CascadePriority;
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+    let pseudo = PseudoElement::from_pseudo_type(pseudo_type, None);
+    let parent_element = if pseudo.is_none() {
+        element.inheritance_parent()
+    } else {
+        Some(element)
+    };
+    let parent_data = parent_element.as_ref().and_then(|e| e.borrow_data());
+    let parent_style = parent_data
+        .as_ref()
+        .map(|d| d.styles.primary())
+        .map(|x| &**x);
+
+    let container_size_query =
+        ContainerSizeQuery::for_element(element, parent_style, pseudo.is_some());
+    let mut conditions = Default::default();
+    let mut context = create_context_for_animation(
+        &data,
+        &style,
+        parent_style,
+        /* for_smil_animation = */ false,
+        &mut conditions,
+        container_size_query,
+    );
+
+    let restriction = pseudo.and_then(|p| p.property_restriction());
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let default_values = data.default_computed_values();
+
+    for (index, keyframe) in keyframes.iter().enumerate() {
+        let ref mut animation_values = computed_keyframes[index];
+
+        let mut seen = PropertyDeclarationIdSet::default();
+        let mut iter = PrioritizedPropertyIter::new(&keyframe.mPropertyValues);
+
+        // FIXME: This is pretty much a hack. Instead, the AnimatedValue should be better
+        // integrated in the cascade. This would allow us to fix revert() too.
+        {
+            let mut builder = CustomPropertiesBuilder::new_with_properties(
+                &data.stylist,
+                style.custom_properties().clone(),
+                &mut context,
+            );
+            let priority = CascadePriority::same_tree_author_normal_at_root_layer();
+            for property in &mut iter {
+                let is_custom = match PropertyId::from_gecko_animated_property_id(&property.mProperty) {
+                    Some(PropertyId::Custom(..)) => true,
+                    _ => false,
+                };
+                if !is_custom {
+                    break; // Custom props are guaranteed to sort earlier.
+                }
+                if property.mServoDeclarationBlock.mRawPtr.is_null() {
+                    continue;
+                }
+                let declarations = unsafe { &*property.mServoDeclarationBlock.mRawPtr };
+                let guard = declarations.read_with(&guard);
+                for decl in guard.normal_declaration_iter() {
+                    if let PropertyDeclaration::Custom(ref declaration) = *decl {
+                        builder.cascade(declaration, priority);
+                    }
+                }
+            }
+            iter.reset();
+            let _deferred= builder.build(DeferFontRelativeCustomPropertyResolution::No);
+            debug_assert!(
+                _deferred.is_none(),
+                "Custom property processing deferred despite specifying otherwise?"
+            );
+        };
+
+        let mut property_index = 0;
+        for property in iter {
+            if simulate_compute_values_failure(property) {
+                continue;
+            }
+
+            let mut maybe_append_animation_value =
+                |property: PropertyDeclarationId, value: Option<AnimationValue>| {
+                    debug_assert!(!property.is_logical());
+                    debug_assert!(property.is_animatable());
+
+                    // 'display' is only animatable from SMIL
+                    if property == PropertyDeclarationId::Longhand(LonghandId::Display) {
+                        return;
+                    }
+
+                    // Skip restricted properties
+                    if restriction.map_or(false, |r| !property.flags().contains(r)) {
+                        return;
+                    }
+
+                    if seen.contains(property) {
+                        return;
+                    }
+                    seen.insert(property);
+
+                    // This is safe since we immediately write to the uninitialized values.
+                    unsafe {
+                        animation_values.set_len((property_index + 1) as u32);
+                        ptr::write(
+                            &mut animation_values[property_index],
+                            structs::PropertyStyleAnimationValuePair {
+                                mProperty: property.to_gecko_animated_property_id(/* owned = */ true),
+                                mValue: structs::AnimationValue {
+                                    mServo: value.map_or(structs::RefPtr::null(), |v| {
+                                        structs::RefPtr::from_arc(Arc::new(v))
+                                    }),
+                                },
+                            },
+                        );
+                    }
+                    property_index += 1;
+                };
+
+            if property.mServoDeclarationBlock.mRawPtr.is_null() {
+                if let Some(prop) =
+                    OwnedPropertyDeclarationId::from_gecko_animated_property_id(&property.mProperty)
+                {
+                    maybe_append_animation_value(prop.as_borrowed(), None);
+                }
+                continue;
+            }
+
+            let declarations = unsafe { &*property.mServoDeclarationBlock.mRawPtr };
+            let guard = declarations.read_with(&guard);
+            let iter = guard.to_animation_value_iter(&mut context, &default_values);
+
+            for value in iter {
+                maybe_append_animation_value(value.id(), Some(value.clone()));
+            }
+        }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetAnimationValues(
+    declarations: &LockedDeclarationBlock,
+    element: &RawGeckoElement,
+    style: &ComputedValues,
+    raw_data: &PerDocumentStyleData,
+    animation_values: &mut ThinVec<structs::RefPtr<AnimationValue>>,
+) {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+    let parent_element = element.inheritance_parent();
+    let parent_data = parent_element.as_ref().and_then(|e| e.borrow_data());
+    let parent_style = parent_data
+        .as_ref()
+        .map(|d| d.styles.primary())
+        .map(|x| &**x);
+
+    let container_size_query =
+        ContainerSizeQuery::for_element(element, None, /* is_pseudo = */ false);
+    let mut conditions = Default::default();
+    let mut context = create_context_for_animation(
+        &data,
+        &style,
+        parent_style,
+        /* for_smil_animation = */ true,
+        &mut conditions,
+        container_size_query,
+    );
+
+    let default_values = data.default_computed_values();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    let guard = declarations.read_with(&guard);
+    let iter = guard.to_animation_value_iter(
+        &mut context,
+        &default_values,
+    );
+    animation_values.extend(iter.map(|v| structs::RefPtr::from_arc(Arc::new(v))));
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_GetPropertyId(
+    value: &AnimationValue,
+    property_id: &mut structs::AnimatedPropertyID,
+) {
+    *property_id = value.id().to_gecko_animated_property_id(/* owned = */ true);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AnimationValue_Compute(
+    element: &RawGeckoElement,
+    declarations: &LockedDeclarationBlock,
+    style: &ComputedValues,
+    raw_data: &PerDocumentStyleData,
+) -> Strong<AnimationValue> {
+    let data = raw_data.borrow();
+
+    let element = GeckoElement(element);
+    let parent_element = element.inheritance_parent();
+    let parent_data = parent_element.as_ref().and_then(|e| e.borrow_data());
+    let parent_style = parent_data
+        .as_ref()
+        .map(|d| d.styles.primary())
+        .map(|x| &**x);
+
+    let container_size_query =
+        ContainerSizeQuery::for_element(element, None, /* is_pseudo = */ false);
+    let mut conditions = Default::default();
+    let mut context = create_context_for_animation(
+        &data,
+        style,
+        parent_style,
+        /* for_smil_animation = */ false,
+        &mut conditions,
+        container_size_query,
+    );
+
+    let default_values = data.default_computed_values();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    // We only compute the first element in declarations.
+    match declarations
+        .read_with(&guard)
+        .declaration_importance_iter()
+        .next()
+    {
+        Some((decl, imp)) if imp == Importance::Normal => {
+            let animation = AnimationValue::from_declaration(
+                decl,
+                &mut context,
+                default_values,
+            );
+            animation.map_or(Strong::null(), |value| Arc::new(value).into())
+        },
+        _ => Strong::null(),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_AssertTreeIsClean(root: &RawGeckoElement) {
+    if !cfg!(feature = "gecko_debug") {
+        panic!("Calling Servo_AssertTreeIsClean in release build");
+    }
+
+    let root = GeckoElement(root);
+    debug!("Servo_AssertTreeIsClean: ");
+    debug!("{:?}", ShowSubtreeData(root.as_node()));
+
+    fn assert_subtree_is_clean<'le>(el: GeckoElement<'le>) {
+        debug_assert!(
+            !el.has_dirty_descendants() && !el.has_animation_only_dirty_descendants(),
+            "{:?} has still dirty bit {:?} or animation-only dirty bit {:?}",
+            el,
+            el.has_dirty_descendants(),
+            el.has_animation_only_dirty_descendants()
+        );
+        for child in el.traversal_children() {
+            if let Some(child) = child.as_element() {
+                assert_subtree_is_clean(child);
+            }
+        }
+    }
+
+    assert_subtree_is_clean(root);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_IsWorkerThread() -> bool {
+    thread_state::get().is_worker()
+}
+
+enum Offset {
+    Zero,
+    One,
+}
+
+fn fill_in_missing_keyframe_values(
+    all_properties: &PropertyDeclarationIdSet,
+    timing_function: &ComputedTimingFunction,
+    properties_at_offset: &PropertyDeclarationIdSet,
+    offset: Offset,
+    keyframes: &mut nsTArray<structs::Keyframe>,
+) {
+    // Return early if all animated properties are already set.
+    if properties_at_offset.contains_all(all_properties) {
+        return;
+    }
+
+    // Use auto for missing keyframes.
+    // FIXME: This may be a spec issue in css-animations-2 because the spec says the default
+    // keyframe-specific composite is replace, but web-animations-1 uses auto. Use auto now so we
+    // use the value of animation-composition of the element, for missing keyframes.
+    // https://github.com/w3c/csswg-drafts/issues/7476
+    let composition = structs::CompositeOperationOrAuto::Auto;
+    let keyframe = match offset {
+        Offset::Zero => unsafe {
+            Gecko_GetOrCreateInitialKeyframe(keyframes, timing_function, composition)
+        },
+        Offset::One => unsafe {
+            Gecko_GetOrCreateFinalKeyframe(keyframes, timing_function, composition)
+        },
+    };
+
+    // Append properties that have not been set at this offset.
+    for property in all_properties.iter() {
+        if !properties_at_offset.contains(property) {
+            unsafe {
+                Gecko_AppendPropertyValuePair(
+                    &mut *(*keyframe).mPropertyValues,
+                    &property.to_gecko_animated_property_id(/* owned = */ false),
+                );
+            }
+        }
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_GetKeyframesForName(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    style: &ComputedValues,
+    name: *mut nsAtom,
+    inherited_timing_function: &ComputedTimingFunction,
+    keyframes: &mut nsTArray<structs::Keyframe>,
+) -> bool {
+    use style::gecko_bindings::structs::CompositeOperationOrAuto;
+    use style::values::computed::AnimationComposition;
+
+    debug_assert!(keyframes.len() == 0, "keyframes should be initially empty");
+
+    let element = GeckoElement(element);
+    let data = raw_data.borrow();
+    let name = Atom::from_raw(name);
+
+    let animation = match data.stylist.get_animation(&name, element) {
+        Some(animation) => animation,
+        None => return false,
+    };
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+
+    let mut properties_set_at_current_offset = PropertyDeclarationIdSet::default();
+    let mut properties_set_at_start = PropertyDeclarationIdSet::default();
+    let mut properties_set_at_end = PropertyDeclarationIdSet::default();
+    let mut has_complete_initial_keyframe = false;
+    let mut has_complete_final_keyframe = false;
+    let mut current_offset = -1.;
+
+    let writing_mode = style.writing_mode;
+
+    // Iterate over the keyframe rules backwards so we can drop overridden
+    // properties (since declarations in later rules override those in earlier
+    // ones).
+    for step in animation.steps.iter().rev() {
+        if step.start_percentage.0 != current_offset {
+            properties_set_at_current_offset.clear();
+            current_offset = step.start_percentage.0;
+        }
+
+        // Override timing_function if the keyframe has an animation-timing-function.
+        let timing_function = match step.get_animation_timing_function(&guard) {
+            Some(val) => val.to_computed_value_without_context(),
+            None => (*inherited_timing_function).clone(),
+        };
+
+        // Override composite operation if the keyframe has an animation-composition.
+        let composition =
+            step.get_animation_composition(&guard)
+                .map_or(CompositeOperationOrAuto::Auto, |val| match val {
+                    AnimationComposition::Replace => CompositeOperationOrAuto::Replace,
+                    AnimationComposition::Add => CompositeOperationOrAuto::Add,
+                    AnimationComposition::Accumulate => CompositeOperationOrAuto::Accumulate,
+                });
+
+        // Look for an existing keyframe with the same offset, timing function, and compsition, or
+        // else add a new keyframe at the beginning of the keyframe array.
+        let keyframe = Gecko_GetOrCreateKeyframeAtStart(
+            keyframes,
+            step.start_percentage.0 as f32,
+            &timing_function,
+            composition,
+        );
+
+        match step.value {
+            KeyframesStepValue::ComputedValues => {
+                // In KeyframesAnimation::from_keyframes if there is no 0% or
+                // 100% keyframe at all, we will create a 'ComputedValues' step
+                // to represent that all properties animated by the keyframes
+                // animation should be set to the underlying computed value for
+                // that keyframe.
+                let mut seen = PropertyDeclarationIdSet::default();
+                for property in animation.properties_changed.iter() {
+                    let property = property.to_physical(writing_mode);
+                    if seen.contains(property) {
+                        continue;
+                    }
+                    seen.insert(property);
+
+                    Gecko_AppendPropertyValuePair(
+                        &mut *(*keyframe).mPropertyValues,
+                        &property.to_gecko_animated_property_id(/* owned = */ false),
+                    );
+                }
+                if current_offset == 0.0 {
+                    has_complete_initial_keyframe = true;
+                } else if current_offset == 1.0 {
+                    has_complete_final_keyframe = true;
+                }
+            },
+            KeyframesStepValue::Declarations { ref block } => {
+                let guard = block.read_with(&guard);
+
+                // Filter out non-animatable properties and properties with
+                // !important.
+                //
+                // Also, iterate in reverse to respect the source order in case
+                // there are logical and physical longhands in the same block.
+                for declaration in guard.normal_declaration_iter().rev() {
+                    let id = declaration.id().to_physical(writing_mode);
+
+                    // Skip non-animatable properties, including the 'display' property because
+                    // although it is animatable from SMIL, it should not be animatable from CSS
+                    // Animations.
+                    if !id.is_animatable() ||
+                        id == PropertyDeclarationId::Longhand(LonghandId::Display)
+                    {
+                        continue;
+                    }
+
+                    if properties_set_at_current_offset.contains(id) {
+                        continue;
+                    }
+
+                    let pair = Gecko_AppendPropertyValuePair(
+                        &mut *(*keyframe).mPropertyValues,
+                        &id.to_gecko_animated_property_id(/* owned = */ false),
+                    );
+
+                    (*pair).mServoDeclarationBlock.set_arc(Arc::new(
+                        global_style_data
+                            .shared_lock
+                            .wrap(PropertyDeclarationBlock::with_one(
+                                declaration.to_physical(writing_mode),
+                                Importance::Normal,
+                            )),
+                    ));
+
+                    if current_offset == 0.0 {
+                        properties_set_at_start.insert(id);
+                    } else if current_offset == 1.0 {
+                        properties_set_at_end.insert(id);
+                    }
+                    properties_set_at_current_offset.insert(id);
+                }
+            },
+        }
+    }
+
+    let mut properties_changed = PropertyDeclarationIdSet::default();
+    for property in animation.properties_changed.iter() {
+        properties_changed.insert(property.to_physical(writing_mode));
+    }
+
+    // Append property values that are missing in the initial or the final keyframes.
+    if !has_complete_initial_keyframe {
+        fill_in_missing_keyframe_values(
+            &properties_changed,
+            inherited_timing_function,
+            &properties_set_at_start,
+            Offset::Zero,
+            keyframes,
+        );
+    }
+    if !has_complete_final_keyframe {
+        fill_in_missing_keyframe_values(
+            &properties_changed,
+            inherited_timing_function,
+            &properties_set_at_end,
+            Offset::One,
+            keyframes,
+        );
+    }
+    true
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_GetFontFaceRules(
+    raw_data: &PerDocumentStyleData,
+    rules: &mut ThinVec<structs::nsFontFaceRuleContainer>,
+) {
+    let data = raw_data.borrow();
+    debug_assert_eq!(rules.len(), 0);
+
+    // Reversed iterator because Gecko expects rules to appear sorted
+    // UserAgent first, Author last.
+    let font_face_iter = data
+        .stylist
+        .iter_extra_data_origins_rev()
+        .flat_map(|(d, o)| d.font_faces.iter().zip(iter::repeat(o)));
+
+    rules.extend(font_face_iter.map(|(&(ref rule, _layer_id), origin)| {
+        structs::nsFontFaceRuleContainer {
+            mRule: structs::RefPtr::from_arc(rule.clone()),
+            mOrigin: origin,
+        }
+    }))
+}
+
+// XXX Ideally this should return a Option<&LockedCounterStyleRule>,
+// but we cannot, because the value from AtomicRefCell::borrow() can only
+// live in this function, and thus anything derived from it cannot get the
+// same lifetime as raw_data in parameter. See bug 1451543.
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleSet_GetCounterStyleRule(
+    raw_data: &PerDocumentStyleData,
+    name: *mut nsAtom,
+) -> *const LockedCounterStyleRule {
+    let data = raw_data.borrow();
+    Atom::with(name, |name| {
+        data.stylist
+            .iter_extra_data_origins()
+            .find_map(|(d, _)| d.counter_styles.get(name))
+            .map_or(ptr::null(), |rule| &**rule as *const _)
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_BuildFontFeatureValueSet(
+    raw_data: &PerDocumentStyleData,
+) -> *mut gfxFontFeatureValueSet {
+    let data = raw_data.borrow();
+
+    let has_rule = data
+        .stylist
+        .iter_extra_data_origins()
+        .any(|(d, _)| !d.font_feature_values.is_empty());
+
+    if !has_rule {
+        return ptr::null_mut();
+    }
+
+    let font_feature_values_iter = data
+        .stylist
+        .iter_extra_data_origins_rev()
+        .flat_map(|(d, _)| d.font_feature_values.iter());
+
+    let set = unsafe { Gecko_ConstructFontFeatureValueSet() };
+    for &(ref rule, _) in font_feature_values_iter {
+        rule.set_at_rules(set);
+    }
+    set
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_BuildFontPaletteValueSet(
+    raw_data: &PerDocumentStyleData,
+) -> *mut FontPaletteValueSet {
+    let data = raw_data.borrow();
+
+    let has_rule = data
+        .stylist
+        .iter_extra_data_origins()
+        .any(|(d, _)| !d.font_palette_values.is_empty());
+
+    if !has_rule {
+        return ptr::null_mut();
+    }
+
+    let font_palette_values_iter = data
+        .stylist
+        .iter_extra_data_origins_rev()
+        .flat_map(|(d, _)| d.font_palette_values.iter());
+
+    let set = unsafe { Gecko_ConstructFontPaletteValueSet() };
+    for &(ref rule, _) in font_palette_values_iter {
+        rule.to_gecko_palette_value_set(set);
+    }
+    set
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_ResolveForDeclarations(
+    raw_data: &PerDocumentStyleData,
+    parent_style_context: Option<&ComputedValues>,
+    declarations: &LockedDeclarationBlock,
+) -> Strong<ComputedValues> {
+    let doc_data = raw_data.borrow();
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let guards = StylesheetGuards::same(&guard);
+
+    let parent_style = match parent_style_context {
+        Some(parent) => &*parent,
+        None => doc_data.default_computed_values(),
+    };
+
+    doc_data
+        .stylist
+        .compute_for_declarations::<GeckoElement>(&guards, parent_style, unsafe {
+            Arc::from_raw_addrefed(declarations)
+        })
+        .into()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_AddSizeOfExcludingThis(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    sizes: *mut ServoStyleSetSizes,
+    raw_data: &PerDocumentStyleData,
+) {
+    let data = raw_data.borrow_mut();
+    let mut ops = MallocSizeOfOps::new(
+        malloc_size_of.unwrap(),
+        Some(malloc_enclosing_size_of.unwrap()),
+        None,
+    );
+    let sizes = unsafe { sizes.as_mut() }.unwrap();
+    data.add_size_of(&mut ops, sizes);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_UACache_AddSizeOf(
+    malloc_size_of: GeckoMallocSizeOf,
+    malloc_enclosing_size_of: GeckoMallocSizeOf,
+    sizes: *mut ServoStyleSetSizes,
+) {
+    let mut ops = MallocSizeOfOps::new(
+        malloc_size_of.unwrap(),
+        Some(malloc_enclosing_size_of.unwrap()),
+        None,
+    );
+    let sizes = unsafe { sizes.as_mut() }.unwrap();
+    add_size_of_ua_cache(&mut ops, sizes);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MightHaveAttributeDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    local_name: *mut nsAtom,
+) -> bool {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+
+    unsafe {
+        AtomIdent::with(local_name, |atom| {
+            data.stylist.any_applicable_rule_data(element, |data| {
+                data.might_have_attribute_dependency(atom)
+            })
+        })
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MightHaveNthOfIDDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    old_id: *mut nsAtom,
+    new_id: *mut nsAtom,
+) -> bool {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+
+    data.stylist.any_applicable_rule_data(element, |data| {
+        [old_id, new_id]
+            .iter()
+            .filter(|id| !id.is_null())
+            .any(|id| unsafe {
+                AtomIdent::with(*id, |atom| data.might_have_nth_of_id_dependency(atom))
+            }) ||
+            data.might_have_nth_of_attribute_dependency(&AtomIdent(atom!("id")))
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MightHaveNthOfClassDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    snapshots: &ServoElementSnapshotTable,
+) -> bool {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+
+    data.stylist.any_applicable_rule_data(element, |data| {
+        classes_changed(&element, snapshots)
+            .iter()
+            .any(|atom| data.might_have_nth_of_class_dependency(atom)) ||
+            data.might_have_nth_of_attribute_dependency(&AtomIdent(atom!("class")))
+    })
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MightHaveNthOfAttributeDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    local_name: *mut nsAtom,
+) -> bool {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+
+    unsafe {
+        AtomIdent::with(local_name, |atom| {
+            data.stylist.any_applicable_rule_data(element, |data| {
+                data.might_have_nth_of_attribute_dependency(atom)
+            })
+        })
+    }
+}
+
+fn on_siblings_invalidated(element: GeckoElement) {
+    let parent = element
+        .traversal_parent()
+        .expect("How could we invalidate siblings without a common parent?");
+    unsafe {
+        parent.set_dirty_descendants();
+        bindings::Gecko_NoteDirtySubtreeForInvalidation(parent.0);
+    }
+}
+
+fn restyle_for_nth_of(element: GeckoElement, flags: ElementSelectorFlags) {
+    debug_assert!(
+        !flags.is_empty(),
+        "Calling restyle for nth but no relevant flag is set."
+    );
+    fn invalidate_siblings_of(
+        element: GeckoElement,
+        get_sibling: fn(GeckoElement) -> Option<GeckoElement>,
+    ) {
+        let mut sibling = get_sibling(element);
+        while let Some(sib) = sibling {
+            if let Some(mut data) = sib.mutate_data() {
+                data.hint.insert(RestyleHint::restyle_subtree());
+            }
+            sibling = get_sibling(sib);
+        }
+    }
+
+    if flags.intersects(ElementSelectorFlags::HAS_SLOW_SELECTOR) {
+        invalidate_siblings_of(element, |e| e.prev_sibling_element());
+    }
+    if flags.intersects(ElementSelectorFlags::HAS_SLOW_SELECTOR_LATER_SIBLINGS) {
+        invalidate_siblings_of(element, |e| e.next_sibling_element());
+    }
+    on_siblings_invalidated(element);
+}
+
+fn relative_selector_invalidated_at(element: GeckoElement, result: &InvalidationResult) {
+    if result.has_invalidated_siblings() {
+        on_siblings_invalidated(element);
+    } else if result.has_invalidated_descendants() {
+        unsafe { bindings::Gecko_NoteDirtySubtreeForInvalidation(element.0) };
+    } else if result.has_invalidated_self() {
+        unsafe { bindings::Gecko_NoteDirtyElement(element.0) };
+        let flags = element
+            .parent_element()
+            .map_or(ElementSelectorFlags::empty(), |e| e.slow_selector_flags());
+        // We invalidated up to the anchor, and it has a flag for nth-of invalidation.
+        if !flags.is_empty() {
+            restyle_for_nth_of(element, flags);
+        }
+    }
+}
+
+fn add_relative_selector_attribute_dependency<'a>(
+    element: &GeckoElement<'a>,
+    scope: &Option<OpaqueElement>,
+    invalidation_map: &'a RelativeSelectorInvalidationMap,
+    attribute: &AtomIdent,
+    collector: &mut RelativeSelectorDependencyCollector<'a, GeckoElement<'a>>,
+) {
+    match invalidation_map
+        .map
+        .other_attribute_affecting_selectors
+        .get(attribute)
+    {
+        Some(v) => {
+            for dependency in v {
+                collector.add_dependency(dependency, *element, *scope);
+            }
+        },
+        None => (),
+    };
+}
+
+fn inherit_relative_selector_search_direction(
+    parent: Option<GeckoElement>,
+    prev_sibling: Option<GeckoElement>,
+) -> ElementSelectorFlags {
+    let mut inherited = ElementSelectorFlags::empty();
+    if let Some(parent) = parent {
+        if let Some(direction) = parent.relative_selector_search_direction() {
+            inherited |= direction
+                .intersection(ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR);
+        }
+    }
+    if let Some(sibling) = prev_sibling {
+        if let Some(direction) = sibling.relative_selector_search_direction() {
+            // Inherit both, for e.g. a sibling with `:has(~.sibling .descendant)`
+            inherited |= direction.intersection(
+                ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_ANCESTOR_SIBLING,
+            );
+        }
+    }
+    inherited
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorIDDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    old_id: *mut nsAtom,
+    new_id: *mut nsAtom,
+    snapshots: &ServoElementSnapshotTable,
+) {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+    let invalidator = RelativeSelectorInvalidator {
+        element,
+        quirks_mode,
+        snapshot_table: Some(snapshots),
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map: SiblingTraversalMap::default(),
+        _marker: std::marker::PhantomData,
+    };
+
+    invalidator.invalidate_relative_selectors_for_this(
+        &data.stylist,
+        |element, scope, data, quirks_mode, collector| {
+            let invalidation_map = data.relative_selector_invalidation_map();
+            relative_selector_dependencies_for_id(
+                old_id,
+                new_id,
+                element,
+                scope,
+                quirks_mode,
+                &invalidation_map,
+                collector,
+            );
+            add_relative_selector_attribute_dependency(
+                element,
+                &scope,
+                invalidation_map,
+                &AtomIdent(atom!("id")),
+                collector,
+            );
+        },
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorClassDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    snapshots: &ServoElementSnapshotTable,
+) {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+    let invalidator = RelativeSelectorInvalidator {
+        element,
+        quirks_mode,
+        snapshot_table: Some(snapshots),
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map: SiblingTraversalMap::default(),
+        _marker: std::marker::PhantomData,
+    };
+
+    invalidator.invalidate_relative_selectors_for_this(
+        &data.stylist,
+        |element, scope, data, quirks_mode, mut collector| {
+            let invalidation_map = data.relative_selector_invalidation_map();
+
+            relative_selector_dependencies_for_class(
+                &classes_changed(element, snapshots),
+                &element,
+                scope,
+                quirks_mode,
+                invalidation_map,
+                collector,
+            );
+            add_relative_selector_attribute_dependency(
+                element,
+                &scope,
+                invalidation_map,
+                &AtomIdent(atom!("class")),
+                &mut collector,
+            );
+        },
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorAttributeDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    local_name: *mut nsAtom,
+    snapshots: &ServoElementSnapshotTable,
+) {
+    let data = raw_data.borrow();
+    let element = GeckoElement(element);
+
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+    unsafe {
+        AtomIdent::with(local_name, |atom| {
+            let invalidator = RelativeSelectorInvalidator {
+                element,
+                quirks_mode,
+                snapshot_table: Some(snapshots),
+                invalidated: relative_selector_invalidated_at,
+                sibling_traversal_map: SiblingTraversalMap::default(),
+                _marker: std::marker::PhantomData,
+            };
+
+            invalidator.invalidate_relative_selectors_for_this(
+                &data.stylist,
+                |element, scope, data, _quirks_mode, mut collector| {
+                    add_relative_selector_attribute_dependency(
+                        element,
+                        &scope,
+                        data.relative_selector_invalidation_map(),
+                        atom,
+                        &mut collector,
+                    );
+                },
+            );
+        })
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorStateDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    state: u64,
+    snapshots: &ServoElementSnapshotTable,
+) {
+    let element = GeckoElement(element);
+
+    let state = match ElementState::from_bits(state) {
+        Some(state) => state,
+        None => return,
+    };
+    let data = raw_data.borrow();
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+
+    let invalidator = RelativeSelectorInvalidator {
+        element,
+        quirks_mode,
+        snapshot_table: Some(snapshots),
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map: SiblingTraversalMap::default(),
+        _marker: std::marker::PhantomData,
+    };
+
+    invalidator.invalidate_relative_selectors_for_this(
+        &data.stylist,
+        |element, scope, data, quirks_mode, collector| {
+            let invalidation_map = data.relative_selector_invalidation_map();
+            invalidation_map
+                .map
+                .state_affecting_selectors
+                .lookup_with_additional(*element, quirks_mode, None, &[], state, |dependency| {
+                    if !dependency.state.intersects(state) {
+                        return true;
+                    }
+                    collector.add_dependency(&dependency.dep, *element, scope);
+                    true
+                });
+        },
+    );
+}
+
+fn invalidate_relative_selector_prev_sibling_side_effect(
+    prev_sibling: GeckoElement,
+    quirks_mode: QuirksMode,
+    sibling_traversal_map: SiblingTraversalMap<GeckoElement>,
+    stylist: &Stylist,
+) {
+    let invalidator = RelativeSelectorInvalidator {
+        element: prev_sibling,
+        quirks_mode,
+        snapshot_table: None,
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map,
+        _marker: std::marker::PhantomData,
+    };
+    invalidator.invalidate_relative_selectors_for_dom_mutation(
+        false,
+        &stylist,
+        ElementSelectorFlags::empty(),
+        DomMutationOperation::SideEffectPrevSibling,
+    );
+}
+
+fn invalidate_relative_selector_next_sibling_side_effect(
+    next_sibling: GeckoElement,
+    quirks_mode: QuirksMode,
+    sibling_traversal_map: SiblingTraversalMap<GeckoElement>,
+    stylist: &Stylist,
+) {
+    let invalidator = RelativeSelectorInvalidator {
+        element: next_sibling,
+        quirks_mode,
+        snapshot_table: None,
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map,
+        _marker: std::marker::PhantomData,
+    };
+    invalidator.invalidate_relative_selectors_for_dom_mutation(
+        false,
+        &stylist,
+        ElementSelectorFlags::empty(),
+        DomMutationOperation::SideEffectNextSibling,
+    );
+}
+
+fn invalidate_relative_selector_ts_dependency(
+    raw_data: &PerDocumentStyleData,
+    element: GeckoElement,
+    state: TSStateForInvalidation,
+) {
+    let data = raw_data.borrow();
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+
+    let invalidator = RelativeSelectorInvalidator {
+        element,
+        quirks_mode,
+        snapshot_table: None,
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map: SiblingTraversalMap::default(),
+        _marker: std::marker::PhantomData,
+    };
+
+    invalidator.invalidate_relative_selectors_for_this(
+        &data.stylist,
+        |element, scope, data, quirks_mode, collector| {
+            let invalidation_map = data.relative_selector_invalidation_map();
+            invalidation_map
+                .ts_state_to_selector
+                .lookup_with_additional(
+                    *element,
+                    quirks_mode,
+                    None,
+                    &[],
+                    ElementState::empty(),
+                    |dependency| {
+                        if !dependency.state.intersects(state) {
+                            return true;
+                        }
+                        collector.add_dependency(&dependency.dep, *element, scope);
+                        true
+                    },
+                );
+        },
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorEmptyDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+) {
+    invalidate_relative_selector_ts_dependency(
+        raw_data,
+        GeckoElement(element),
+        TSStateForInvalidation::EMPTY,
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorNthEdgeDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+) {
+    invalidate_relative_selector_ts_dependency(
+        raw_data,
+        GeckoElement(element),
+        TSStateForInvalidation::NTH_EDGE,
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorNthDependencyFromSibling(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+) {
+    let mut element = Some(GeckoElement(element));
+
+    // Short of doing the actual matching, any of the siblings can match the selector, so we
+    // have to try invalidating against all of them.
+    while let Some(sibling) = element {
+        invalidate_relative_selector_ts_dependency(raw_data, sibling, TSStateForInvalidation::NTH);
+        element = sibling.next_sibling_element();
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorForInsertion(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+) {
+    let element = GeckoElement(element);
+    let data = raw_data.borrow();
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+
+    let inherited =
+        inherit_relative_selector_search_direction(element.parent_element(), element.prev_sibling_element());
+    // Technically, we're not handling breakouts, where the anchor is a (later-sibling) descendant.
+    // For descendant case, we're ok since it's a descendant of an element yet to be styled.
+    // For later-sibling descendant, `HAS_SLOW_SELECTOR_LATER_SIBLINGS` is set anyway.
+    if inherited.is_empty() {
+        return;
+    }
+
+    // Ok, we could've been inserted between two sibling elements that were connected
+    // through next sibling. This can happen in two ways:
+    // * `.a:has(+ .b)`
+    // * `:has(.. .a + .b ..)`
+    // Note that the previous sibling may be the anchor, and not part of the invalidation chain.
+    // Either way, there must be siblings to both sides of the element being inserted
+    // to consider it.
+    match (
+        element.prev_sibling_element(),
+        element.next_sibling_element(),
+    ) {
+        (Some(prev_sibling), Some(next_sibling)) => 'sibling: {
+            // If the prev sibling is not on the sibling search path, skip.
+            if prev_sibling
+                .relative_selector_search_direction()
+                .map_or(true, |direction| {
+                    !direction.intersects(
+                        ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_SIBLING,
+                    )
+                })
+            {
+                break 'sibling;
+            }
+            element.apply_selector_flags(
+                ElementSelectorFlags::RELATIVE_SELECTOR_SEARCH_DIRECTION_SIBLING,
+            );
+            invalidate_relative_selector_prev_sibling_side_effect(
+                prev_sibling,
+                quirks_mode,
+                SiblingTraversalMap::new(
+                    prev_sibling,
+                    prev_sibling.prev_sibling_element(),
+                    element.next_sibling_element(),
+                ), // Pretend this inserted element isn't here.
+                &data.stylist,
+            );
+            invalidate_relative_selector_next_sibling_side_effect(
+                next_sibling,
+                quirks_mode,
+                SiblingTraversalMap::new(
+                    next_sibling,
+                    Some(prev_sibling),
+                    next_sibling.next_sibling_element(),
+                ),
+                &data.stylist,
+            );
+        },
+        _ => (),
+    };
+
+    let invalidator = RelativeSelectorInvalidator {
+        element,
+        quirks_mode,
+        snapshot_table: None,
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map: SiblingTraversalMap::default(),
+        _marker: std::marker::PhantomData,
+    };
+
+    invalidator.invalidate_relative_selectors_for_dom_mutation(
+        true,
+        &data.stylist,
+        inherited,
+        DomMutationOperation::Insert,
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorForAppend(
+    raw_data: &PerDocumentStyleData,
+    first_node: &RawGeckoNode,
+) {
+    let first_node = GeckoNode(first_node);
+    let inherited = inherit_relative_selector_search_direction(
+        first_node.parent_element(),
+        first_node.prev_sibling_element(),
+    );
+    if inherited.is_empty() {
+        return;
+    }
+    let first_element = if let Some(e) = first_node.as_element() {
+        e
+    } else if let Some(e) = first_node.next_sibling_element() {
+        e
+    } else {
+        return;
+    };
+    let data = raw_data.borrow();
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+
+    let mut element = Some(first_element);
+    while let Some(e) = element {
+        let invalidator = RelativeSelectorInvalidator {
+            element: e,
+            quirks_mode,
+            snapshot_table: None,
+            sibling_traversal_map: SiblingTraversalMap::default(),
+            invalidated: relative_selector_invalidated_at,
+            _marker: std::marker::PhantomData,
+        };
+        invalidator.invalidate_relative_selectors_for_dom_mutation(
+            true,
+            &data.stylist,
+            inherited,
+            DomMutationOperation::Append,
+        );
+        element = e.next_sibling_element();
+    }
+}
+
+fn get_siblings_of_element<'e>(
+    element: GeckoElement<'e>,
+    following_node: &'e Option<GeckoNode<'e>>,
+) -> (Option<GeckoElement<'e>>, Option<GeckoElement<'e>>) {
+    let node = match following_node {
+        Some(n) => n,
+        None => return match element.as_node().parent_node() {
+            Some(p) => (p.last_child_element(), None),
+            None => (None, None),
+        },
+    };
+
+    (node.prev_sibling_element(), node.next_sibling_element())
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_MaybeInvalidateRelativeSelectorForRemoval(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    following_node: Option<&RawGeckoNode>,
+) {
+    let element = GeckoElement(element);
+
+    // This element was in-tree, so we can safely say that if it was not on
+    // the relative selector search path, its removal will not invalidate any
+    // relative selector.
+    if element.relative_selector_search_direction().is_none() {
+        return;
+    }
+    let following_node = following_node.map(GeckoNode);
+    let (prev_sibling, next_sibling) =
+        get_siblings_of_element(element, &following_node);
+    let data = raw_data.borrow();
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+
+    let inherited = inherit_relative_selector_search_direction(element.parent_element(), prev_sibling);
+    if inherited.is_empty() {
+        return;
+    }
+
+    // Same comment as insertion applies.
+    match (prev_sibling, next_sibling) {
+        (Some(prev_sibling), Some(next_sibling)) => {
+            invalidate_relative_selector_prev_sibling_side_effect(
+                prev_sibling,
+                quirks_mode,
+                SiblingTraversalMap::default(),
+                &data.stylist,
+            );
+            invalidate_relative_selector_next_sibling_side_effect(
+                next_sibling,
+                quirks_mode,
+                SiblingTraversalMap::default(),
+                &data.stylist,
+            );
+        },
+        _ => (),
+    };
+    let invalidator = RelativeSelectorInvalidator {
+        element,
+        quirks_mode,
+        snapshot_table: None,
+        sibling_traversal_map: SiblingTraversalMap::new(element, prev_sibling, next_sibling),
+        invalidated: relative_selector_invalidated_at,
+        _marker: std::marker::PhantomData,
+    };
+    invalidator.invalidate_relative_selectors_for_dom_mutation(
+        true,
+        &data.stylist,
+        inherited,
+        DomMutationOperation::Remove,
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_HasStateDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    state: u64,
+) -> bool {
+    let element = GeckoElement(element);
+
+    let state = ElementState::from_bits_retain(state);
+    let data = raw_data.borrow();
+
+    data.stylist
+        .any_applicable_rule_data(element, |data| data.has_state_dependency(state))
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_HasNthOfStateDependency(
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    state: u64,
+) -> bool {
+    let element = GeckoElement(element);
+
+    let state = ElementState::from_bits_retain(state);
+    let data = raw_data.borrow();
+
+    data.stylist
+        .any_applicable_rule_data(element, |data| data.has_nth_of_state_dependency(state))
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_RestyleSiblingsForNthOf(element: &RawGeckoElement, flags: u32) {
+    let flags = slow_selector_flags_from_node_selector_flags(flags);
+    let element = GeckoElement(element);
+    restyle_for_nth_of(element, flags);
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_StyleSet_HasDocumentStateDependency(
+    raw_data: &PerDocumentStyleData,
+    state: u64,
+) -> bool {
+    let state = DocumentState::from_bits_retain(state);
+    let data = raw_data.borrow();
+
+    data.stylist.has_document_state_dependency(state)
+}
+
+fn computed_or_resolved_value(
+    style: &ComputedValues,
+    prop: nsCSSPropertyID,
+    context: Option<&style::values::resolved::Context>,
+    value: &mut nsACString,
+) {
+    if let Some(longhand) = LonghandId::from_nscsspropertyid(prop) {
+        return style
+            .computed_or_resolved_value(longhand, context, value)
+            .unwrap();
+    }
+
+    let shorthand =
+        ShorthandId::from_nscsspropertyid(prop).expect("Not a shorthand nor a longhand?");
+    let mut block = PropertyDeclarationBlock::new();
+    for longhand in shorthand.longhands() {
+        block.push(
+            style.computed_or_resolved_declaration(longhand, context),
+            Importance::Normal,
+        );
+    }
+    block.shorthand_to_css(shorthand, value).unwrap();
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_GetComputedValue(
+    style: &ComputedValues,
+    prop: nsCSSPropertyID,
+    value: &mut nsACString,
+) {
+    computed_or_resolved_value(style, prop, None, value)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_GetResolvedValue(
+    style: &ComputedValues,
+    prop: nsCSSPropertyID,
+    raw_data: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    value: &mut nsACString,
+) {
+    use style::values::resolved;
+
+    let data = raw_data.borrow();
+    let device = data.stylist.device();
+    let context = resolved::Context {
+        style,
+        device,
+        element_info: resolved::ResolvedElementInfo {
+            element: GeckoElement(element),
+        },
+    };
+
+    computed_or_resolved_value(style, prop, Some(&context), value)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_GetCustomPropertyValue(
+    computed_values: &ComputedValues,
+    raw_style_set: &PerDocumentStyleData,
+    name: &nsACString,
+    value: &mut nsACString,
+) -> bool {
+    let doc_data = raw_style_set.borrow();
+    let name = Atom::from(name.as_str_unchecked());
+    let custom_registration = doc_data.stylist.get_custom_property_registration(&name);
+    let computed_value = if custom_registration.inherits() {
+        computed_values.custom_properties.inherited.get(&name)
+    } else {
+        computed_values.custom_properties.non_inherited.get(&name)
+    };
+
+    if let Some(v) = computed_value {
+        v.to_css(&mut CssWriter::new(value)).unwrap();
+        true
+    } else {
+        false
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetCustomPropertiesCount(computed_values: &ComputedValues) -> u32 {
+    // Just expose the custom property items from custom_properties.inherited
+    // and custom_properties.non_inherited.
+    let properties = computed_values.custom_properties();
+    properties.inherited.len() as u32 + properties.non_inherited.len() as u32
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetCustomPropertyNameAt(
+    computed_values: &ComputedValues,
+    index: u32,
+) -> *mut nsAtom {
+    match &computed_values
+        .custom_properties
+        .property_at(index as usize)
+    {
+        Some((name, _value)) => name.as_ptr(),
+        None => ptr::null_mut(),
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_CssUrl_IsLocalRef(url: &url::CssUrl) -> bool {
+    url.is_fragment()
+}
+
+fn relative_selector_dependencies_for_id<'a>(
+    old_id: *const nsAtom,
+    new_id: *const nsAtom,
+    element: &GeckoElement<'a>,
+    scope: Option<OpaqueElement>,
+    quirks_mode: QuirksMode,
+    invalidation_map: &'a RelativeSelectorInvalidationMap,
+    collector: &mut RelativeSelectorDependencyCollector<'a, GeckoElement<'a>>,
+) {
+    [old_id, new_id]
+        .iter()
+        .filter(|id| !id.is_null())
+        .for_each(|id| unsafe {
+            AtomIdent::with(*id, |atom| {
+                match invalidation_map.map.id_to_selector.get(atom, quirks_mode) {
+                    Some(v) => {
+                        for dependency in v {
+                            collector.add_dependency(dependency, *element, scope);
+                        }
+                    },
+                    None => (),
+                };
+            })
+        });
+}
+
+fn relative_selector_dependencies_for_class<'a>(
+    classes_changed: &SmallVec<[Atom; 8]>,
+    element: &GeckoElement<'a>,
+    scope: Option<OpaqueElement>,
+    quirks_mode: QuirksMode,
+    invalidation_map: &'a RelativeSelectorInvalidationMap,
+    collector: &mut RelativeSelectorDependencyCollector<'a, GeckoElement<'a>>,
+) {
+    classes_changed.iter().for_each(|atom| {
+        match invalidation_map
+            .map
+            .class_to_selector
+            .get(atom, quirks_mode)
+        {
+            Some(v) => {
+                for dependency in v {
+                    collector.add_dependency(dependency, *element, scope);
+                }
+            },
+            None => (),
+        };
+    });
+}
+
+fn process_relative_selector_invalidations(
+    element: &GeckoElement,
+    snapshot_table: &ServoElementSnapshotTable,
+    data: &PerDocumentStyleDataImpl,
+) {
+    let snapshot = match snapshot_table.get(element) {
+        None => return,
+        Some(s) => s,
+    };
+    let mut states = None;
+    let mut classes = None;
+
+    let quirks_mode: QuirksMode = data.stylist.quirks_mode();
+    let invalidator = RelativeSelectorInvalidator {
+        element: *element,
+        quirks_mode,
+        invalidated: relative_selector_invalidated_at,
+        sibling_traversal_map: SiblingTraversalMap::default(),
+        snapshot_table: Some(snapshot_table),
+        _marker: std::marker::PhantomData,
+    };
+
+    invalidator.invalidate_relative_selectors_for_this(
+        &data.stylist,
+        |element, scope, data, quirks_mode, collector| {
+            let invalidation_map = data.relative_selector_invalidation_map();
+            let states = *states.get_or_insert_with(|| {
+                ElementWrapper::new(*element, snapshot_table).state_changes()
+            });
+            let classes = classes.get_or_insert_with(|| classes_changed(element, snapshot_table));
+            if snapshot.id_changed() {
+                relative_selector_dependencies_for_id(
+                    element
+                        .id()
+                        .map(|id| id.as_ptr().cast_const())
+                        .unwrap_or(ptr::null()),
+                    snapshot
+                        .id_attr()
+                        .map(|id| id.as_ptr().cast_const())
+                        .unwrap_or(ptr::null()),
+                    element,
+                    scope,
+                    quirks_mode,
+                    invalidation_map,
+                    collector,
+                );
+            }
+            relative_selector_dependencies_for_class(
+                &classes,
+                element,
+                scope,
+                quirks_mode,
+                invalidation_map,
+                collector,
+            );
+            snapshot.each_attr_changed(|attr| {
+                add_relative_selector_attribute_dependency(
+                    element,
+                    &scope,
+                    invalidation_map,
+                    attr,
+                    collector,
+                )
+            });
+            invalidation_map
+                .map
+                .state_affecting_selectors
+                .lookup_with_additional(*element, quirks_mode, None, &[], states, |dependency| {
+                    if !dependency.state.intersects(states) {
+                        return true;
+                    }
+                    collector.add_dependency(&dependency.dep, *element, scope);
+                    true
+                });
+        },
+    );
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ProcessInvalidations(
+    set: &PerDocumentStyleData,
+    element: &RawGeckoElement,
+    snapshots: *const ServoElementSnapshotTable,
+) {
+    debug_assert!(!snapshots.is_null());
+
+    let element = GeckoElement(element);
+    debug_assert!(element.has_snapshot());
+    debug_assert!(!element.handled_snapshot());
+
+    let snapshot_table = unsafe { &*snapshots };
+    let per_doc_data = set.borrow();
+    process_relative_selector_invalidations(&element, snapshot_table, &per_doc_data);
+
+    let mut data = element.mutate_data();
+    if data.is_none() {
+        // Snapshot for unstyled element is really only meant for relative selector
+        // invalidation, so this is fine.
+        return;
+    }
+
+    let global_style_data = &*GLOBAL_STYLE_DATA;
+    let guard = global_style_data.shared_lock.read();
+    let per_doc_data = set.borrow();
+    let shared_style_context = create_shared_context(
+        &global_style_data,
+        &guard,
+        &per_doc_data.stylist,
+        TraversalFlags::empty(),
+        snapshot_table,
+    );
+    let mut data = data.as_mut().map(|d| &mut **d);
+
+    let mut selector_caches = SelectorCaches::default();
+    if let Some(ref mut data) = data {
+        // FIXME(emilio): Ideally we could share the nth-index-cache across all
+        // the elements?
+        let result = data.invalidate_style_if_needed(
+            element,
+            &shared_style_context,
+            None,
+            &mut selector_caches,
+        );
+
+        if result.has_invalidated_siblings() {
+            let parent = element
+                .traversal_parent()
+                .expect("How could we invalidate siblings without a common parent?");
+            unsafe {
+                parent.set_dirty_descendants();
+                bindings::Gecko_NoteDirtySubtreeForInvalidation(parent.0);
+            }
+        } else if result.has_invalidated_descendants() {
+            unsafe { bindings::Gecko_NoteDirtySubtreeForInvalidation(element.0) };
+        } else if result.has_invalidated_self() {
+            unsafe { bindings::Gecko_NoteDirtyElement(element.0) };
+        }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_HasPendingRestyleAncestor(
+    element: &RawGeckoElement,
+    may_need_to_flush_layout: bool,
+) -> bool {
+    let mut has_yet_to_be_styled = false;
+    let mut element = Some(GeckoElement(element));
+    while let Some(e) = element {
+        if e.has_any_animation() {
+            return true;
+        }
+
+        // If the element needs a frame, it means that we haven't styled it yet
+        // after it got inserted in the document, and thus we may need to do
+        // that for transitions and animations to trigger.
+        //
+        // This is a fast path in the common case, but `has_yet_to_be_styled` is
+        // the real check for this.
+        if e.needs_frame() {
+            return true;
+        }
+
+        let data = e.borrow_data();
+        if let Some(ref data) = data {
+            if !data.hint.is_empty() {
+                return true;
+            }
+            if has_yet_to_be_styled && !data.styles.is_display_none() {
+                return true;
+            }
+            // Ideally, DOM mutations wouldn't affect layout trees of siblings.
+            //
+            // In practice, this can happen because Gecko deals pretty badly
+            // with some kinds of content insertion and removals.
+            //
+            // If we may need to flush layout, we need frames to accurately
+            // determine whether we'll actually flush, so if we have to
+            // reconstruct we need to flush style, which is what will take care
+            // of ensuring that frames are constructed, even if the style itself
+            // is up-to-date.
+            if may_need_to_flush_layout && data.damage.contains(GeckoRestyleDamage::reconstruct()) {
+                return true;
+            }
+        }
+        has_yet_to_be_styled = data.is_none();
+
+        element = e.traversal_parent();
+    }
+    false
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SelectorList_Parse(
+    selector_list: &nsACString,
+    is_chrome: bool,
+) -> *mut SelectorList {
+    use style::selector_parser::SelectorParser;
+
+    let url_data = UrlExtraData::from_ptr_ref(if is_chrome {
+        &DUMMY_CHROME_URL_DATA
+    } else {
+        &DUMMY_URL_DATA
+    });
+
+    let input = selector_list.as_str_unchecked();
+    let selector_list = match SelectorParser::parse_author_origin_no_namespace(&input, url_data) {
+        Ok(selector_list) => selector_list,
+        Err(..) => return ptr::null_mut(),
+    };
+
+    Box::into_raw(Box::new(selector_list))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SelectorList_Drop(list: *mut SelectorList) {
+    let _ = Box::from_raw(list);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_IsValidCSSColor(value: &nsACString) -> bool {
+    let mut input = ParserInput::new(value.as_str_unchecked());
+    let mut input = Parser::new(&mut input);
+    let context = ParserContext::new(
+        Origin::Author,
+        dummy_url_data(),
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    specified::Color::is_valid(&context, &mut input)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ComputeColor(
+    raw_data: Option<&PerDocumentStyleData>,
+    current_color: structs::nscolor,
+    value: &nsACString,
+    result_color: &mut structs::nscolor,
+    was_current_color: *mut bool,
+    loader: *mut Loader,
+) -> bool {
+    let mut input = ParserInput::new(value.as_str_unchecked());
+    let mut input = Parser::new(&mut input);
+    let reporter = loader.as_mut().and_then(|loader| {
+        // Make an ErrorReporter that will report errors as being "from DOM".
+        ErrorReporter::new(ptr::null_mut(), loader, ptr::null_mut())
+    });
+
+    let context = ParserContext::new(
+        Origin::Author,
+        dummy_url_data(),
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        reporter.as_ref().map(|e| e as &dyn ParseErrorReporter),
+        None,
+    );
+
+    let data;
+    let device = match raw_data {
+        Some(d) => {
+            data = d.borrow();
+            Some(data.stylist.device())
+        },
+        None => None,
+    };
+
+    let computed = match specified::Color::parse_and_compute(&context, &mut input, device) {
+        Some(c) => c,
+        None => return false,
+    };
+
+    let current_color = style::gecko::values::convert_nscolor_to_absolute_color(current_color);
+    if !was_current_color.is_null() {
+        *was_current_color = computed.is_currentcolor();
+    }
+
+    let rgba = computed.resolve_to_absolute(&current_color);
+    *result_color = style::gecko::values::convert_absolute_color_to_nscolor(&rgba);
+    true
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ResolveColor(
+    color: &computed::Color,
+    foreground: &style::color::AbsoluteColor,
+) -> style::color::AbsoluteColor {
+    color.resolve_to_absolute(foreground)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ResolveCalcLengthPercentage(
+    calc: &computed::length_percentage::CalcLengthPercentage,
+    basis: f32,
+) -> f32 {
+    calc.resolve(computed::Length::new(basis)).px()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ConvertColorSpace(
+    color: &AbsoluteColor,
+    color_space: ColorSpace,
+) -> AbsoluteColor {
+    color.to_color_space(color_space)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_IntersectionObserverRootMargin_Parse(
+    value: &nsACString,
+    result: *mut IntersectionObserverRootMargin,
+) -> bool {
+    let value = value.as_str_unchecked();
+    let result = result.as_mut().unwrap();
+
+    let mut input = ParserInput::new(&value);
+    let mut parser = Parser::new(&mut input);
+
+    let url_data = dummy_url_data();
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    let margin = parser.parse_entirely(|p| IntersectionObserverRootMargin::parse(&context, p));
+    match margin {
+        Ok(margin) => {
+            *result = margin;
+            true
+        },
+        Err(..) => false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_IntersectionObserverRootMargin_ToString(
+    root_margin: &IntersectionObserverRootMargin,
+    result: &mut nsACString,
+) {
+    let mut writer = CssWriter::new(result);
+    root_margin.to_css(&mut writer).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ParseTransformIntoMatrix(
+    value: &nsACString,
+    contain_3d: &mut bool,
+    result: &mut structs::Matrix4x4Components,
+) -> bool {
+    use style::properties::longhands::transform;
+
+    let string = unsafe { value.as_str_unchecked() };
+    let mut input = ParserInput::new(&string);
+    let mut parser = Parser::new(&mut input);
+    let context = ParserContext::new(
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    let transform = match parser.parse_entirely(|t| transform::parse(&context, t)) {
+        Ok(t) => t,
+        Err(..) => return false,
+    };
+
+    let (m, is_3d) = match transform.to_transform_3d_matrix(None) {
+        Ok(result) => result,
+        Err(..) => return false,
+    };
+
+    *result = m.to_array();
+    *contain_3d = is_3d;
+    true
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ParseFilters(
+    value: &nsACString,
+    ignore_urls: bool,
+    data: *mut URLExtraData,
+    out: &mut style::OwnedSlice<Filter>,
+) -> bool {
+    use style::values::specified::effects::SpecifiedFilter;
+
+    let string = unsafe { value.as_str_unchecked() };
+    let mut input = ParserInput::new(&string);
+    let mut parser = Parser::new(&mut input);
+    let url_data = unsafe { UrlExtraData::from_ptr_ref(&data) };
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        None,
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    let mut filters = vec![];
+
+    if parser
+        .try_parse(|i| i.expect_ident_matching("none"))
+        .is_ok()
+    {
+        return parser.expect_exhausted().is_ok();
+    }
+
+    if parser.is_exhausted() {
+        return false;
+    }
+
+    while !parser.is_exhausted() {
+        let specified_filter = match SpecifiedFilter::parse(&context, &mut parser) {
+            Ok(f) => f,
+            Err(..) => return false,
+        };
+
+        let filter = match specified_filter.to_computed_value_without_context() {
+            Ok(f) => f,
+            Err(..) => return false,
+        };
+
+        if ignore_urls && matches!(filter, Filter::Url(_)) {
+            continue;
+        }
+
+        filters.push(filter);
+    }
+
+    *out = style::OwnedSlice::from(filters);
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_ParseFontShorthandForMatching(
+    value: &nsACString,
+    data: *mut URLExtraData,
+    family: &mut FontFamilyList,
+    style: &mut FontStyle,
+    stretch: &mut FontStretch,
+    weight: &mut FontWeight,
+    size: Option<&mut f32>,
+    small_caps: Option<&mut bool>,
+) -> bool {
+    use style::properties::shorthands::font;
+    use style::values::generics::font::FontStyle as GenericFontStyle;
+    use style::values::specified::font as specified;
+
+    let string = value.as_str_unchecked();
+    let mut input = ParserInput::new(&string);
+    let mut parser = Parser::new(&mut input);
+    let url_data = UrlExtraData::from_ptr_ref(&data);
+    let context = ParserContext::new(
+        Origin::Author,
+        url_data,
+        Some(CssRuleType::FontFace),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    let font = match parser.parse_entirely(|f| font::parse_value(&context, f)) {
+        Ok(f) => f,
+        Err(..) => return false,
+    };
+
+    // The system font is not acceptable, so we return false.
+    match font.font_family {
+        specified::FontFamily::Values(list) => *family = list,
+        specified::FontFamily::System(_) => return false,
+    }
+
+    let specified_font_style = match font.font_style {
+        specified::FontStyle::Specified(ref s) => s,
+        specified::FontStyle::System(_) => return false,
+    };
+
+    *style = match *specified_font_style {
+        GenericFontStyle::Normal => FontStyle::NORMAL,
+        GenericFontStyle::Italic => FontStyle::ITALIC,
+        GenericFontStyle::Oblique(ref angle) => FontStyle::oblique(angle.degrees()),
+    };
+
+    *stretch = match font.font_stretch {
+        specified::FontStretch::Keyword(ref k) => k.compute(),
+        specified::FontStretch::Stretch(ref p) => FontStretch::from_percentage(p.0.get()),
+        specified::FontStretch::System(_) => return false,
+    };
+
+    *weight = match font.font_weight {
+        specified::FontWeight::Absolute(w) => w.compute(),
+        // Resolve relative font weights against the initial of font-weight
+        // (normal, which is equivalent to 400).
+        specified::FontWeight::Bolder => FontWeight::normal().bolder(),
+        specified::FontWeight::Lighter => FontWeight::normal().lighter(),
+        specified::FontWeight::System(_) => return false,
+    };
+
+    // XXX This is unfinished; see values::specified::FontSize::ToComputedValue
+    // for a more complete implementation (but we can't use it as-is).
+    if let Some(size) = size {
+        *size = match font.font_size {
+            specified::FontSize::Length(lp) => {
+                use style::values::generics::transform::ToAbsoluteLength;
+                match lp.to_pixel_length(None) {
+                    Ok(len) => len,
+                    Err(..) => return false,
+                }
+            },
+            specified::FontSize::Keyword(info) => {
+                let keyword = if info.kw != specified::FontSizeKeyword::Math {
+                    info.kw
+                } else {
+                    specified::FontSizeKeyword::Medium
+                };
+                // Map absolute-size keywords to sizes.
+                // TODO: Maybe get a meaningful quirks / base size from the caller?
+                let quirks_mode = QuirksMode::NoQuirks;
+                keyword
+                    .to_length_without_context(
+                        quirks_mode,
+                        computed::Length::new(specified::FONT_MEDIUM_PX),
+                    )
+                    .0
+                    .px()
+            },
+            // smaller, larger not currently supported
+            specified::FontSize::Smaller |
+            specified::FontSize::Larger |
+            specified::FontSize::System(_) => {
+                return false;
+            },
+        };
+    }
+
+    if let Some(small_caps) = small_caps {
+        use style::computed_values::font_variant_caps::T::SmallCaps;
+        *small_caps = font.font_variant_caps == SmallCaps;
+    }
+
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SourceSizeList_Parse(value: &nsACString) -> *mut SourceSizeList {
+    let value = value.as_str_unchecked();
+    let mut input = ParserInput::new(value);
+    let mut parser = Parser::new(&mut input);
+
+    let context = ParserContext::new(
+        Origin::Author,
+        dummy_url_data(),
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+
+    // NB: Intentionally not calling parse_entirely.
+    let list = SourceSizeList::parse(&context, &mut parser);
+    Box::into_raw(Box::new(list))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SourceSizeList_Evaluate(
+    raw_data: &PerDocumentStyleData,
+    list: Option<&SourceSizeList>,
+) -> i32 {
+    let doc_data = raw_data.borrow();
+    let device = doc_data.stylist.device();
+    let quirks_mode = doc_data.stylist.quirks_mode();
+
+    let result = match list {
+        Some(list) => list.evaluate(device, quirks_mode),
+        None => SourceSizeList::empty().evaluate(device, quirks_mode),
+    };
+
+    result.0
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SourceSizeList_Drop(list: *mut SourceSizeList) {
+    let _ = Box::from_raw(list);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_InvalidateStyleForDocStateChanges(
+    root: &RawGeckoElement,
+    document_style: &PerDocumentStyleData,
+    non_document_styles: &nsTArray<&AuthorStyles>,
+    states_changed: u64,
+) {
+    use style::invalidation::element::document_state::DocumentStateInvalidationProcessor;
+    use style::invalidation::element::invalidator::TreeStyleInvalidator;
+
+    let document_data = document_style.borrow();
+
+    let iter = document_data
+        .stylist
+        .iter_origins()
+        .map(|(data, _origin)| data)
+        .chain(
+            non_document_styles
+                .iter()
+                .map(|author_styles| &*author_styles.data),
+        );
+
+    let mut selector_caches = SelectorCaches::default();
+    let root = GeckoElement(root);
+    let mut processor = DocumentStateInvalidationProcessor::new(
+        iter,
+        DocumentState::from_bits_retain(states_changed),
+        &mut selector_caches,
+        root.as_node().owner_doc().quirks_mode(),
+    );
+
+    let result =
+        TreeStyleInvalidator::new(root, /* stack_limit_checker = */ None, &mut processor)
+            .invalidate();
+
+    debug_assert!(!result.has_invalidated_siblings(), "How in the world?");
+    if result.has_invalidated_descendants() {
+        bindings::Gecko_NoteDirtySubtreeForInvalidation(root.0);
+    } else if result.has_invalidated_self() {
+        bindings::Gecko_NoteDirtyElement(root.0);
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_PseudoClass_GetStates(name: &nsACString) -> u64 {
+    let name = name.as_str_unchecked();
+    match NonTSPseudoClass::parse_non_functional(name) {
+        None => 0,
+        // Ignore :any-link since it contains both visited and unvisited state.
+        Some(NonTSPseudoClass::AnyLink) => 0,
+        Some(pseudo_class) => pseudo_class.state_flag().bits(),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_UseCounters_Create() -> *mut UseCounters {
+    Box::into_raw(Box::<UseCounters>::default())
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_UseCounters_Drop(c: *mut UseCounters) {
+    let _ = Box::from_raw(c);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_UseCounters_Merge(
+    doc_counters: &UseCounters,
+    sheet_counters: &UseCounters,
+) {
+    doc_counters.merge(sheet_counters)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_IsPropertyIdRecordedInUseCounter(
+    use_counters: &UseCounters,
+    id: nsCSSPropertyID,
+) -> bool {
+    let id = NonCustomPropertyId::from_nscsspropertyid(id).unwrap();
+    use_counters.non_custom_properties.recorded(id)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_IsUnknownPropertyRecordedInUseCounter(
+    use_counters: &UseCounters,
+    p: CountedUnknownProperty,
+) -> bool {
+    use_counters.counted_unknown_properties.recorded(p)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_IsCssPropertyRecordedInUseCounter(
+    use_counters: &UseCounters,
+    property: &nsACString,
+    known_prop: *mut bool,
+) -> bool {
+    *known_prop = false;
+
+    let prop_name = property.as_str_unchecked();
+    if let Ok(p) = PropertyId::parse_unchecked_for_testing(prop_name) {
+        if let Some(id) = p.non_custom_id() {
+            *known_prop = true;
+            return use_counters.non_custom_properties.recorded(id);
+        }
+    }
+
+    if let Some(p) = CountedUnknownProperty::parse_for_testing(prop_name) {
+        *known_prop = true;
+        return use_counters.counted_unknown_properties.recorded(p);
+    }
+
+    false
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SharedMemoryBuilder_Create(
+    buffer: *mut u8,
+    len: usize,
+) -> *mut SharedMemoryBuilder {
+    Box::into_raw(Box::new(SharedMemoryBuilder::new(buffer, len)))
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SharedMemoryBuilder_AddStylesheet(
+    builder: &mut SharedMemoryBuilder,
+    contents: &StylesheetContents,
+    error_message: &mut nsACString,
+) -> *const LockedCssRules {
+    // Assert some things we assume when we create a style sheet from shared
+    // memory.
+    debug_assert_eq!(contents.origin, Origin::UserAgent);
+    debug_assert_eq!(contents.quirks_mode, QuirksMode::NoQuirks);
+    debug_assert!(contents.source_map_url.read().is_none());
+    debug_assert!(contents.source_url.read().is_none());
+
+    match builder.write(&contents.rules) {
+        Ok(rules_ptr) => &**rules_ptr,
+        Err(message) => {
+            error_message.assign(&message);
+            ptr::null()
+        },
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SharedMemoryBuilder_GetLength(
+    builder: &SharedMemoryBuilder,
+) -> usize {
+    builder.len()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_SharedMemoryBuilder_Drop(builder: *mut SharedMemoryBuilder) {
+    let _ = Box::from_raw(builder);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_StyleArcSlice_EmptyPtr() -> *mut c_void {
+    style_traits::arc_slice::ArcSlice::<u64>::leaked_empty_ptr()
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_LoadData_GetLazy(
+    source: &url::LoadDataSource,
+) -> *const url::LoadData {
+    source.get()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_LengthPercentage_ToCss(
+    lp: &computed::LengthPercentage,
+    result: &mut nsACString,
+) {
+    lp.to_css(&mut CssWriter::new(result)).unwrap();
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontStyle_ToCss(s: &FontStyle, result: &mut nsACString) {
+    s.to_css(&mut CssWriter::new(result)).unwrap()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontWeight_ToCss(w: &FontWeight, result: &mut nsACString) {
+    w.to_css(&mut CssWriter::new(result)).unwrap()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontStretch_ToCss(s: &FontStretch, result: &mut nsACString) {
+    s.to_css(&mut CssWriter::new(result)).unwrap()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontStretch_SerializeKeyword(
+    s: &FontStretch,
+    result: &mut nsACString,
+) -> bool {
+    let kw = match s.as_keyword() {
+        Some(kw) => kw,
+        None => return false,
+    };
+    kw.to_css(&mut CssWriter::new(result)).unwrap();
+    true
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_CursorKind_Parse(
+    cursor: &nsACString,
+    result: &mut computed::ui::CursorKind,
+) -> bool {
+    match computed::ui::CursorKind::from_ident(cursor.as_str_unchecked()) {
+        Ok(c) => {
+            *result = c;
+            true
+        },
+        Err(..) => false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFamily_Generic(generic: GenericFontFamily) -> &'static FontFamily {
+    FontFamily::generic(generic)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFamily_ForSystemFont(name: &nsACString, out: &mut FontFamily) {
+    *out = FontFamily::for_system_font(&name.to_utf8());
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FontFamilyList_WithNames(
+    names: &nsTArray<computed::font::SingleFontFamily>,
+    out: &mut FontFamilyList,
+) {
+    *out = FontFamilyList {
+        list: style_traits::arc_slice::ArcSlice::from_iter(names.iter().cloned()),
+    };
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_FamilyName_Serialize(name: &FamilyName, result: &mut nsACString) {
+    name.to_css(&mut CssWriter::new(result)).unwrap()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GenericFontFamily_Parse(input: &nsACString) -> GenericFontFamily {
+    let context = ParserContext::new(
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    let value = input.to_utf8();
+    let mut input = ParserInput::new(&value);
+    let mut input = Parser::new(&mut input);
+    GenericFontFamily::parse(&context, &mut input).unwrap_or(GenericFontFamily::None)
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ColorScheme_Parse(input: &nsACString, out: &mut u8) -> bool {
+    use style::values::specified::ColorScheme;
+
+    let context = ParserContext::new(
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        Some(CssRuleType::Style),
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    let input = unsafe { input.as_str_unchecked() };
+    let mut input = ParserInput::new(&input);
+    let mut input = Parser::new(&mut input);
+    let scheme = match input.parse_entirely(|i| ColorScheme::parse(&context, i)) {
+        Ok(scheme) => scheme,
+        Err(..) => return false,
+    };
+    *out = scheme.raw_bits();
+    true
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_LayerBlockRule_GetName(rule: &LayerBlockRule, result: &mut nsACString) {
+    if let Some(ref name) = rule.name {
+        name.to_css(&mut CssWriter::new(result)).unwrap()
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_LayerStatementRule_GetNameCount(rule: &LayerStatementRule) -> usize {
+    rule.names.len()
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_LayerStatementRule_GetNameAt(
+    rule: &LayerStatementRule,
+    index: usize,
+    result: &mut nsACString,
+) {
+    if let Some(ref name) = rule.names.get(index) {
+        name.to_css(&mut CssWriter::new(result)).unwrap()
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_InvalidateForViewportUnits(
+    document_style: &PerDocumentStyleData,
+    root: &RawGeckoElement,
+    dynamic_only: bool,
+) {
+    let mut document_data = document_style.borrow_mut();
+    let ref mut stylist = document_data.stylist;
+    let device = stylist.device();
+
+    if !device.used_viewport_size() {
+        return;
+    }
+
+    if dynamic_only && !device.used_dynamic_viewport_size() {
+        return;
+    }
+
+    // If the viewport changed, then initial values containing viewport units need to be recomputed.
+    if stylist
+        .get_custom_property_initial_values_flags()
+        .intersects(ComputedValueFlags::USES_VIEWPORT_UNITS)
+    {
+        stylist.rebuild_initial_values_for_custom_properties();
+    }
+
+    if style::invalidation::viewport_units::invalidate(GeckoElement(root)) {
+        // The invalidation machinery propagates the bits up, but we still need
+        // to tell the Gecko restyle root machinery about it.
+        bindings::Gecko_NoteDirtySubtreeForInvalidation(root);
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_InterpolateColor(
+    interpolation: ColorInterpolationMethod,
+    left: &AbsoluteColor,
+    right: &AbsoluteColor,
+    progress: f32,
+) -> AbsoluteColor {
+    style::color::mix::mix(
+        interpolation,
+        left,
+        progress,
+        right,
+        1.0 - progress,
+        ColorMixFlags::empty(),
+    )
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_EasingFunctionAt(
+    easing_function: &ComputedTimingFunction,
+    progress: f64,
+    before_flag: BeforeFlag,
+) -> f64 {
+    easing_function.calculate_output(progress, before_flag, 1e-7)
+}
+
+fn parse_no_context<'i, F, R>(string: &'i str, parse: F) -> Result<R, ()>
+where
+    F: FnOnce(&ParserContext, &mut Parser<'i, '_>) -> Result<R, ParseError<'i>>,
+{
+    let context = ParserContext::new(
+        Origin::Author,
+        unsafe { dummy_url_data() },
+        None,
+        ParsingMode::DEFAULT,
+        QuirksMode::NoQuirks,
+        /* namespaces = */ Default::default(),
+        None,
+        None,
+    );
+    let mut input = ParserInput::new(string);
+    Parser::new(&mut input)
+        .parse_entirely(|i| parse(&context, i))
+        .map_err(|_| ())
+}
+
+#[no_mangle]
+// Parse a length without style context (for canvas2d letterSpacing/wordSpacing attributes).
+// This accepts absolute lengths, and if a font-metrics-getter function is passed, also
+// font-relative ones, but not other units (such as percentages, viewport-relative, etc)
+// that would require a full style context to resolve.
+pub extern "C" fn Servo_ParseLengthWithoutStyleContext(
+    len: &nsACString,
+    out: &mut f32,
+    get_font_metrics: Option<unsafe extern "C" fn(*mut c_void) -> GeckoFontMetrics>,
+    getter_context: *mut c_void,
+) -> bool {
+    let metrics_getter = if let Some(getter) = get_font_metrics {
+        Some(move || -> GeckoFontMetrics { unsafe { getter(getter_context) } })
+    } else {
+        None
+    };
+    let value = parse_no_context(unsafe { len.as_str_unchecked() }, specified::Length::parse)
+        .and_then(|p| p.to_computed_pixel_length_with_font_metrics(metrics_getter));
+    match value {
+        Ok(v) => {
+            *out = v;
+            true
+        },
+        Err(..) => false,
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_SlowRgbToColorName(r: u8, g: u8, b: u8, result: &mut nsACString) -> bool {
+    let mut candidates = SmallVec::<[&'static str; 5]>::new();
+    for (name, color) in cssparser::color::all_named_colors() {
+        if color == (r, g, b) {
+            candidates.push(name);
+        }
+    }
+    if candidates.is_empty() {
+        return false;
+    }
+    // DevTools expect the first alphabetically.
+    candidates.sort();
+    result.assign(candidates[0]);
+    true
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_ColorNameToRgb(name: &nsACString, out: &mut structs::nscolor) -> bool {
+    match cssparser::color::parse_named_color(unsafe { name.as_str_unchecked() }) {
+        Ok((r, g, b)) => {
+            *out = style::gecko::values::convert_absolute_color_to_nscolor(&AbsoluteColor::new(
+                ColorSpace::Srgb,
+                r,
+                g,
+                b,
+                1.0,
+            ));
+            true
+        },
+        _ => false,
+    }
+}
+
+#[repr(u8)]
+pub enum RegisterCustomPropertyResult {
+    SuccessfullyRegistered,
+    InvalidName,
+    AlreadyRegistered,
+    InvalidSyntax,
+    NoInitialValue,
+    InvalidInitialValue,
+    InitialValueNotComputationallyIndependent,
+}
+
+/// https://drafts.css-houdini.org/css-properties-values-api-1/#the-registerproperty-function
+#[no_mangle]
+pub extern "C" fn Servo_RegisterCustomProperty(
+    per_doc_data: &PerDocumentStyleData,
+    extra_data: *mut URLExtraData,
+    name: &nsACString,
+    syntax: &nsACString,
+    inherits: bool,
+    initial_value: Option<&nsACString>,
+) -> RegisterCustomPropertyResult {
+    use self::RegisterCustomPropertyResult::*;
+    use style::custom_properties::SpecifiedValue;
+    use style::properties_and_values::rule::{PropertyRegistrationError, PropertyRuleName};
+    use style::properties_and_values::syntax::Descriptor;
+
+    let mut per_doc_data = per_doc_data.borrow_mut();
+    let url_data = unsafe { UrlExtraData::from_ptr_ref(&extra_data) };
+    let name = unsafe { name.as_str_unchecked() };
+    let syntax = unsafe { syntax.as_str_unchecked() };
+    let initial_value = initial_value.map(|v| unsafe { v.as_str_unchecked() });
+
+    // If name is not a custom property name string, throw a SyntaxError and exit this algorithm.
+    let name = match style::custom_properties::parse_name(name) {
+        Ok(n) => Atom::from(n),
+        Err(()) => return InvalidName,
+    };
+
+    // If property set already contains an entry with name as its property name (compared
+    // codepoint-wise), throw an InvalidModificationError and exit this algorithm.
+    if per_doc_data
+        .stylist
+        .custom_property_script_registry()
+        .get(&name)
+        .is_some()
+    {
+        return AlreadyRegistered;
+    }
+    // Attempt to consume a syntax definition from syntax. If it returns failure, throw a
+    // SyntaxError. Otherwise, let syntax definition be the returned syntax definition.
+    let Ok(syntax) = Descriptor::from_str(syntax, /* preserve_specified = */ false) else {
+        return InvalidSyntax;
+    };
+
+    let initial_value = match initial_value {
+        Some(v) => {
+            let mut input = ParserInput::new(v);
+            let parsed = Parser::new(&mut input)
+                .parse_entirely(|input| {
+                    input.skip_whitespace();
+                    SpecifiedValue::parse(input, url_data).map(Arc::new)
+                })
+                .ok();
+            if parsed.is_none() {
+                return InvalidInitialValue;
+            }
+            parsed
+        },
+        None => None,
+    };
+
+    if let Err(error) =
+        PropertyRegistration::validate_initial_value(&syntax, initial_value.as_deref())
+    {
+        return match error {
+            PropertyRegistrationError::InitialValueNotComputationallyIndependent => {
+                InitialValueNotComputationallyIndependent
+            },
+            PropertyRegistrationError::InvalidInitialValue => InvalidInitialValue,
+            PropertyRegistrationError::NoInitialValue => NoInitialValue,
+        };
+    }
+
+    per_doc_data
+        .stylist
+        .custom_property_script_registry_mut()
+        .register(PropertyRegistration {
+            name: PropertyRuleName(name),
+            data: PropertyRegistrationData {
+                syntax,
+                inherits: if inherits {
+                    PropertyInherits::True
+                } else {
+                    PropertyInherits::False
+                },
+                initial_value,
+            },
+            url_data: url_data.clone(),
+            source_location: SourceLocation { line: 0, column: 0 },
+        });
+
+    per_doc_data
+        .stylist
+        .rebuild_initial_values_for_custom_properties();
+
+    SuccessfullyRegistered
+}
+
+#[repr(C)]
+pub struct PropDef {
+    // The name of the property.
+    pub name: Atom,
+    // The syntax of the property.
+    pub syntax: nsCString,
+    // Whether the property inherits.
+    pub inherits: bool,
+    pub has_initial_value: bool,
+    pub initial_value: nsCString,
+    // True if the property was set with CSS.registerProperty
+    pub from_js: bool,
+}
+
+impl PropDef {
+    /// Creates a PropDef from a name and a PropertyRegistration.
+    pub fn new(name: Atom, property_registration: &PropertyRegistration, from_js: bool) -> Self {
+        let mut syntax = nsCString::new();
+        if let Some(spec) = property_registration.data.syntax.specified_string() {
+            syntax.assign(spec);
+        } else {
+            // FIXME: Descriptor::to_css should behave consistently (probably this shouldn't use
+            // the ToCss trait).
+            property_registration
+                .data
+                .syntax
+                .to_css(&mut CssWriter::new(&mut syntax))
+                .unwrap();
+        };
+        let initial_value = property_registration.data.initial_value.to_css_nscstring();
+        PropDef {
+            name,
+            syntax,
+            inherits: property_registration.data.inherits(),
+            has_initial_value: property_registration.data.initial_value.is_some(),
+            initial_value,
+            from_js,
+        }
+    }
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetRegisteredCustomProperties(
+    per_doc_data: &PerDocumentStyleData,
+    custom_properties: &mut ThinVec<PropDef>,
+) {
+    let stylist = &per_doc_data.borrow().stylist;
+
+    custom_properties.extend(
+        stylist
+            .custom_property_script_registry()
+            .get_all()
+            .iter()
+            .map(|(name, property_registration)| {
+                PropDef::new(name.clone(), property_registration, /* from_js */ true)
+            }),
+    );
+
+    for (cascade_data, _origin) in stylist.iter_origins() {
+        custom_properties.extend(cascade_data.custom_property_registrations().iter().map(
+            |(name, value)| {
+                let property_registration = &value.last().unwrap().0;
+                PropDef::new(
+                    name.clone(),
+                    property_registration,
+                    /* from_js */
+                    false,
+                )
+            },
+        ))
+    }
+}
+
+#[repr(C)]
+pub struct SelectorWarningData {
+    /// Index to the selector generating the warning.
+    pub index: usize,
+    /// Kind of the warning.
+    pub kind: SelectorWarningKind,
+}
+
+#[no_mangle]
+pub extern "C" fn Servo_GetSelectorWarnings(
+    rule: &LockedStyleRule,
+    warnings: &mut ThinVec<SelectorWarningData>,
+) {
+    read_locked_arc(rule, |r| {
+        for (i, selector) in r.selectors.slice().iter().enumerate() {
+            for k in SelectorWarningKind::from_selector(selector) {
+                warnings.push(SelectorWarningData { index: i, kind: k });
+            }
+        }
+    });
+}
diff --git a/servo/ports/geckolib/lib.rs b/servo/ports/geckolib/lib.rs
new file mode 100644
index 0000000000..c11f6ab36e
--- /dev/null
+++ b/servo/ports/geckolib/lib.rs
@@ -0,0 +1,36 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+extern crate bincode;
+extern crate cssparser;
+#[macro_use]
+extern crate cstr;
+extern crate dom;
+#[macro_use]
+extern crate gecko_profiler;
+extern crate libc;
+#[macro_use]
+extern crate log;
+extern crate malloc_size_of;
+extern crate nsstring;
+extern crate num_traits;
+extern crate selectors;
+extern crate servo_arc;
+extern crate smallvec;
+#[macro_use]
+extern crate style;
+extern crate style_traits;
+extern crate thin_vec;
+extern crate to_shmem;
+
+mod error_reporter;
+#[allow(non_snake_case)]
+pub mod glue;
+mod stylesheet_loader;
+
+// FIXME(bholley): This should probably go away once we harmonize the allocators.
+#[no_mangle]
+pub extern "C" fn je_malloc_usable_size(_: *const ::libc::c_void) -> ::libc::size_t {
+    0
+}
diff --git a/servo/ports/geckolib/stylesheet_loader.rs b/servo/ports/geckolib/stylesheet_loader.rs
new file mode 100644
index 0000000000..08706fa6a8
--- /dev/null
+++ b/servo/ports/geckolib/stylesheet_loader.rs
@@ -0,0 +1,200 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use cssparser::SourceLocation;
+use nsstring::nsCString;
+use servo_arc::Arc;
+use style::context::QuirksMode;
+use style::gecko::data::GeckoStyleSheet;
+use style::gecko_bindings::bindings;
+use style::gecko_bindings::bindings::Gecko_LoadStyleSheet;
+use style::gecko_bindings::structs::{Loader, LoaderReusableStyleSheets};
+use style::gecko_bindings::structs::{
+    SheetLoadData, SheetLoadDataHolder, StyleSheet as DomStyleSheet,
+};
+use style::gecko_bindings::sugar::refptr::RefPtr;
+use style::global_style_data::GLOBAL_STYLE_DATA;
+use style::media_queries::MediaList;
+use style::parser::ParserContext;
+use style::shared_lock::{Locked, SharedRwLock};
+use style::stylesheets::import_rule::{ImportLayer, ImportSheet, ImportSupportsCondition};
+use style::stylesheets::AllowImportRules;
+use style::stylesheets::{ImportRule, Origin, StylesheetLoader as StyleStylesheetLoader};
+use style::stylesheets::{StylesheetContents, UrlExtraData};
+use style::use_counters::UseCounters;
+use style::values::CssUrl;
+
+pub struct StylesheetLoader(
+    *mut Loader,
+    *mut DomStyleSheet,
+    *mut SheetLoadData,
+    *mut LoaderReusableStyleSheets,
+);
+
+impl StylesheetLoader {
+    pub fn new(
+        loader: *mut Loader,
+        parent: *mut DomStyleSheet,
+        parent_load_data: *mut SheetLoadData,
+        reusable_sheets: *mut LoaderReusableStyleSheets,
+    ) -> Self {
+        StylesheetLoader(loader, parent, parent_load_data, reusable_sheets)
+    }
+}
+
+impl StyleStylesheetLoader for StylesheetLoader {
+    fn request_stylesheet(
+        &self,
+        url: CssUrl,
+        source_location: SourceLocation,
+        _context: &ParserContext,
+        lock: &SharedRwLock,
+        media: Arc<Locked<MediaList>>,
+        supports: Option<ImportSupportsCondition>,
+        layer: ImportLayer,
+    ) -> Arc<Locked<ImportRule>> {
+        // Ensure the supports conditions for this @import are true, if not, refuse to load
+        if !supports.as_ref().map_or(true, |s| s.enabled) {
+            return Arc::new(lock.wrap(ImportRule {
+                url,
+                stylesheet: ImportSheet::new_refused(),
+                supports,
+                layer,
+                source_location,
+            }));
+        }
+
+        // After we get this raw pointer ImportRule will be moved into a lock and Arc
+        // and so the Arc<Url> pointer inside will also move,
+        // but the Url it points to or the allocating backing the String inside that Url won’t,
+        // so this raw pointer will still be valid.
+
+        let child_sheet =
+            unsafe { Gecko_LoadStyleSheet(self.0, self.1, self.2, self.3, &url, media.into()) };
+
+        debug_assert!(
+            !child_sheet.is_null(),
+            "Import rules should always have a strong sheet"
+        );
+        let sheet = unsafe { GeckoStyleSheet::from_addrefed(child_sheet) };
+        let stylesheet = ImportSheet::new(sheet);
+        Arc::new(lock.wrap(ImportRule {
+            url,
+            stylesheet,
+            supports,
+            layer,
+            source_location,
+        }))
+    }
+}
+
+pub struct AsyncStylesheetParser {
+    load_data: RefPtr<SheetLoadDataHolder>,
+    extra_data: UrlExtraData,
+    bytes: nsCString,
+    origin: Origin,
+    quirks_mode: QuirksMode,
+    should_record_use_counters: bool,
+    allow_import_rules: AllowImportRules,
+}
+
+impl AsyncStylesheetParser {
+    pub fn new(
+        load_data: RefPtr<SheetLoadDataHolder>,
+        extra_data: UrlExtraData,
+        bytes: nsCString,
+        origin: Origin,
+        quirks_mode: QuirksMode,
+        should_record_use_counters: bool,
+        allow_import_rules: AllowImportRules,
+    ) -> Self {
+        AsyncStylesheetParser {
+            load_data,
+            extra_data,
+            bytes,
+            origin,
+            quirks_mode,
+            should_record_use_counters,
+            allow_import_rules,
+        }
+    }
+
+    pub fn parse(self) {
+        let global_style_data = &*GLOBAL_STYLE_DATA;
+        let input: &str = unsafe { (*self.bytes).as_str_unchecked() };
+
+        let use_counters = if self.should_record_use_counters {
+            Some(Box::new(UseCounters::default()))
+        } else {
+            None
+        };
+
+        // Note: Parallel CSS parsing doesn't report CSS errors. When errors are
+        // being logged, Gecko prevents the parallel parsing path from running.
+        let sheet = StylesheetContents::from_str(
+            input,
+            self.extra_data.clone(),
+            self.origin,
+            &global_style_data.shared_lock,
+            Some(&self),
+            None,
+            self.quirks_mode.into(),
+            use_counters.as_deref(),
+            self.allow_import_rules,
+            /* sanitized_output = */ None,
+        );
+
+        unsafe {
+            bindings::Gecko_StyleSheet_FinishAsyncParse(
+                self.load_data.get(),
+                sheet.into(),
+                use_counters.map_or(std::ptr::null_mut(), Box::into_raw),
+            );
+        }
+    }
+}
+
+impl StyleStylesheetLoader for AsyncStylesheetParser {
+    fn request_stylesheet(
+        &self,
+        url: CssUrl,
+        source_location: SourceLocation,
+        _context: &ParserContext,
+        lock: &SharedRwLock,
+        media: Arc<Locked<MediaList>>,
+        supports: Option<ImportSupportsCondition>,
+        layer: ImportLayer,
+    ) -> Arc<Locked<ImportRule>> {
+        // Ensure the supports conditions for this @import are true, if not, refuse to load
+        if !supports.as_ref().map_or(true, |s| s.enabled) {
+            return Arc::new(lock.wrap(ImportRule {
+                url: url.clone(),
+                stylesheet: ImportSheet::new_refused(),
+                supports,
+                layer,
+                source_location,
+            }));
+        }
+
+        let stylesheet = ImportSheet::new_pending();
+        let rule = Arc::new(lock.wrap(ImportRule {
+            url: url.clone(),
+            stylesheet,
+            supports,
+            layer,
+            source_location,
+        }));
+
+        unsafe {
+            bindings::Gecko_LoadStyleSheetAsync(
+                self.load_data.get(),
+                &url,
+                media.into(),
+                rule.clone().into(),
+            );
+        }
+
+        rule
+    }
+}
diff --git a/servo/ports/geckolib/tests/Cargo.toml b/servo/ports/geckolib/tests/Cargo.toml
new file mode 100644
index 0000000000..124ba91d96
--- /dev/null
+++ b/servo/ports/geckolib/tests/Cargo.toml
@@ -0,0 +1,14 @@
+[package]
+name = "stylo_tests"
+version = "0.0.1"
+authors = ["The Servo Project Developers"]
+license = "MPL-2.0"
+
+[lib]
+name = "stylo_tests"
+path = "lib.rs"
+doctest = false
+
+[dependencies]
+style = {path = "../../../components/style", features = ["gecko"]}
+euclid = "0.22"
diff --git a/servo/ports/geckolib/tests/lib.rs b/servo/ports/geckolib/tests/lib.rs
new file mode 100644
index 0000000000..40e361a2d5
--- /dev/null
+++ b/servo/ports/geckolib/tests/lib.rs
@@ -0,0 +1,17 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+// Disable this entire crate on Windows when Gecko symbols are not available
+// as linking would fail:
+// https://github.com/rust-lang/rust/pull/44603#issuecomment-338807312
+//
+// On Linux and OS X linking succeeds anyway.
+// Presumably these symbol declarations don’t need to be resolved
+// as they’re not used in any code called from this crate.
+#![cfg(any(linking_with_gecko, not(windows)))]
+
+extern crate euclid;
+extern crate style;
+
+mod piecewise_linear;
diff --git a/servo/ports/geckolib/tests/piecewise_linear.rs b/servo/ports/geckolib/tests/piecewise_linear.rs
new file mode 100644
index 0000000000..728c76638a
--- /dev/null
+++ b/servo/ports/geckolib/tests/piecewise_linear.rs
@@ -0,0 +1,345 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use euclid::approxeq::ApproxEq;
+use style::piecewise_linear::{PiecewiseLinearFunction, PiecewiseLinearFunctionBuilder};
+
+fn get_linear_keyword_equivalent() -> PiecewiseLinearFunction {
+    PiecewiseLinearFunctionBuilder::default().build()
+}
+#[test]
+fn linear_keyword_equivalent_in_bound() {
+    let function = get_linear_keyword_equivalent();
+    assert!(function.at(0.).approx_eq(&0.));
+    assert!(function.at(0.5).approx_eq(&0.5));
+    assert!(function.at(1.0).approx_eq(&1.0));
+}
+
+#[test]
+fn linear_keyword_equivalent_out_of_bounds() {
+    let function = get_linear_keyword_equivalent();
+    assert!(function.at(-0.1).approx_eq(&-0.1));
+    assert!(function.at(1.1).approx_eq(&1.1));
+}
+
+fn get_const_function() -> PiecewiseLinearFunction {
+    let mut builder = PiecewiseLinearFunctionBuilder::default();
+    builder.push(CONST_VALUE as f32, None);
+    builder.build()
+}
+
+const CONST_VALUE: f32 = 0.2;
+
+#[test]
+fn const_function() {
+    let function = get_const_function();
+    assert!(function.at(0.).approx_eq(&CONST_VALUE));
+    assert!(function.at(0.5).approx_eq(&CONST_VALUE));
+    assert!(function.at(1.0).approx_eq(&CONST_VALUE));
+}
+
+#[test]
+fn const_function_out_of_bounds() {
+    let function = get_const_function();
+    assert!(function.at(-0.1).approx_eq(&CONST_VALUE));
+    assert!(function.at(1.1).approx_eq(&CONST_VALUE));
+}
+
+#[test]
+fn implied_input_spacing() {
+    let explicit_spacing = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    let implied_spacing = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, None);
+        builder.push(1.0, None);
+        builder.build()
+    };
+
+    assert!(implied_spacing.at(0.).approx_eq(&explicit_spacing.at(0.)));
+    assert!(implied_spacing.at(0.5).approx_eq(&explicit_spacing.at(0.5)));
+    assert!(implied_spacing.at(1.0).approx_eq(&explicit_spacing.at(1.0)));
+}
+
+#[test]
+fn interpolation() {
+    let interpolate = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, None);
+        builder.push(0.7, None);
+        builder.push(1.0, None);
+        builder.build()
+    };
+    assert!(interpolate.at(0.1).approx_eq(&0.14));
+    assert!(interpolate.at(0.25).approx_eq(&0.35));
+    assert!(interpolate.at(0.45).approx_eq(&0.63));
+    assert!(interpolate.at(0.7).approx_eq(&0.82));
+    assert!(interpolate.at(0.75).approx_eq(&0.85));
+    assert!(interpolate.at(0.95).approx_eq(&0.97));
+}
+
+#[test]
+fn implied_multiple_input_spacing() {
+    let multiple_implied = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, None);
+        builder.push(0.8, None);
+        builder.push(0.6, None);
+        builder.push(0.4, None);
+        builder.push(0.5, Some(0.4));
+        builder.push(0.1, None);
+        builder.push(0.9, None);
+        builder.push(1.0, None);
+        builder.build()
+    };
+    assert!(multiple_implied.at(0.1).approx_eq(&0.8));
+    assert!(multiple_implied.at(0.2).approx_eq(&0.6));
+    assert!(multiple_implied.at(0.3).approx_eq(&0.4));
+    assert!(multiple_implied.at(0.4).approx_eq(&0.5));
+    assert!(multiple_implied.at(0.6).approx_eq(&0.1));
+    assert!(multiple_implied.at(0.8).approx_eq(&0.9));
+    assert!(multiple_implied.at(1.).approx_eq(&1.));
+}
+
+#[test]
+fn nonzero_edge_values() {
+    let nonzero_edges = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.1, Some(0.0));
+        builder.push(0.7, Some(1.0));
+        builder.build()
+    };
+    assert!(nonzero_edges.at(0.).approx_eq(&0.1));
+    assert!(nonzero_edges.at(0.5).approx_eq(&0.4));
+    assert!(nonzero_edges.at(1.0).approx_eq(&0.7));
+}
+
+#[test]
+fn out_of_bounds_extrapolate() {
+    // General case: extrapolate from the edges' slope
+    let oob_extend = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, None);
+        builder.push(0.7, None);
+        builder.push(1.0, None);
+        builder.build()
+    };
+    assert!(oob_extend.at(-0.25).approx_eq(&-0.35));
+    assert!(oob_extend.at(1.25).approx_eq(&1.15));
+}
+
+#[test]
+fn out_of_bounds_flat() {
+    // Repeated endpoints: flat extrapolation out-of-bounds
+    let oob_flat = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.0, Some(0.0));
+        builder.push(0.7, None);
+        builder.push(1.0, Some(1.0));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(oob_flat.at(0.0).approx_eq(&oob_flat.at(-0.25)));
+    assert!(oob_flat.at(1.0).approx_eq(&oob_flat.at(1.25)));
+}
+
+#[test]
+fn flat_region() {
+    let flat = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.5, Some(0.25));
+        builder.push(0.5, Some(0.7));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(flat.at(0.125).approx_eq(&0.25));
+    assert!(flat.at(0.5).approx_eq(&0.5));
+    assert!(flat.at(0.85).approx_eq(&0.75));
+}
+
+#[test]
+fn step() {
+    let step = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.0, Some(0.5));
+        builder.push(1.0, Some(0.5));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(step.at(0.25).approx_eq(&0.0));
+    // At the discontinuity, take the right hand side value
+    assert!(step.at(0.5).approx_eq(&1.0));
+    assert!(step.at(0.75).approx_eq(&1.0));
+}
+
+#[test]
+fn step_multiple_conflicting() {
+    let step = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.0, Some(0.5));
+        builder.push(0.75, Some(0.5));
+        builder.push(0.75, Some(0.5));
+        builder.push(1.0, Some(0.5));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(step.at(0.25).approx_eq(&0.0));
+    assert!(step.at(0.5).approx_eq(&1.0));
+    assert!(step.at(0.75).approx_eq(&1.0));
+}
+
+#[test]
+fn always_monotonic() {
+    let monotonic = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.3, Some(0.5));
+        builder.push(0.4, Some(0.4));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(monotonic.at(0.25).approx_eq(&0.15));
+    // A discontinuity at x = 0.5 from y = 0.3 to 0.4
+    assert!(monotonic.at(0.5).approx_eq(&0.4));
+    assert!(monotonic.at(0.6).approx_eq(&0.52));
+}
+
+#[test]
+fn always_monotonic_flat() {
+    let monotonic = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.2, Some(0.2));
+        builder.push(0.4, Some(0.1));
+        builder.push(0.4, Some(0.15));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(monotonic.at(0.2).approx_eq(&0.4));
+    // A discontinuity at x = 0.2 from y = 0.2 to 0.4
+    assert!(monotonic.at(0.3).approx_eq(&0.475));
+}
+
+#[test]
+fn always_monotonic_flat_backwards() {
+    let monotonic = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.2, Some(0.2));
+        builder.push(0.3, Some(0.3));
+        builder.push(0.3, Some(0.2));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(monotonic.at(0.2).approx_eq(&0.2));
+    assert!(monotonic.at(0.3).approx_eq(&0.3));
+    assert!(monotonic.at(0.4).approx_eq(&0.4));
+}
+
+#[test]
+fn input_out_of_bounds() {
+    let oob = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(-0.5));
+        builder.push(1.0, Some(1.5));
+        builder.build()
+    };
+    assert!(oob.at(-0.5).approx_eq(&0.0));
+    assert!(oob.at(0.0).approx_eq(&0.25));
+    assert!(oob.at(0.5).approx_eq(&0.5));
+    assert!(oob.at(1.0).approx_eq(&0.75));
+    assert!(oob.at(1.5).approx_eq(&1.0));
+}
+
+#[test]
+fn invalid_builder_input() {
+    let built_from_invalid = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(f32::NEG_INFINITY));
+        builder.push(0.7, Some(f32::NAN));
+        builder.push(1.0, Some(f32::INFINITY));
+        builder.build()
+    };
+    let equivalent = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, None);
+        builder.push(0.7, None);
+        builder.push(1.0, None);
+        builder.build()
+    };
+
+    assert!(built_from_invalid.at(0.0).approx_eq(&equivalent.at(0.0)));
+    assert!(built_from_invalid.at(0.25).approx_eq(&equivalent.at(0.25)));
+    assert!(built_from_invalid.at(0.5).approx_eq(&equivalent.at(0.5)));
+    assert!(built_from_invalid.at(0.75).approx_eq(&equivalent.at(0.75)));
+    assert!(built_from_invalid.at(1.0).approx_eq(&equivalent.at(1.0)));
+}
+
+#[test]
+fn input_domain_not_complete() {
+    let not_covered = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.2, Some(0.2));
+        builder.push(0.8, Some(0.8));
+        builder.build()
+    };
+    assert!(not_covered.at(0.0).approx_eq(&0.0));
+    assert!(not_covered.at(0.5).approx_eq(&0.5));
+    assert!(not_covered.at(1.0).approx_eq(&1.0));
+}
+
+#[test]
+fn input_second_negative() {
+    let function = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, None);
+        builder.push(0.0, Some(-0.1));
+        builder.push(0.3, Some(-0.05));
+        builder.push(0.5, None);
+        builder.push(0.2, Some(0.6));
+        builder.push(1.0, None);
+        builder.build()
+    };
+    let equivalent = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(0.0, Some(0.0));
+        builder.push(0.3, Some(0.0));
+        builder.push(0.5, Some(0.3));
+        builder.push(0.2, Some(0.6));
+        builder.push(1.0, Some(1.0));
+        builder.build()
+    };
+    assert!(function.at(-0.1).approx_eq(&equivalent.at(-0.1)));
+    assert!(function.at(0.0).approx_eq(&equivalent.at(0.0)));
+    assert!(function.at(0.3).approx_eq(&equivalent.at(0.3)));
+    assert!(function.at(0.6).approx_eq(&equivalent.at(0.6)));
+    assert!(function.at(1.0).approx_eq(&equivalent.at(1.0)));
+}
+
+#[test]
+fn input_second_last_above_1() {
+    let function = {
+        let mut builder = PiecewiseLinearFunctionBuilder::default();
+        builder.push(0.0, Some(0.0));
+        builder.push(1.0, Some(2.0));
+        builder.push(1.0, None);
+        builder.build()
+    };
+    assert!(function.at(-0.5).approx_eq(&-0.25));
+    assert!(function.at(0.0).approx_eq(&0.0));
+    assert!(function.at(0.5).approx_eq(&0.25));
+    assert!(function.at(1.0).approx_eq(&0.5));
+    assert!(function.at(1.5).approx_eq(&0.75));
+    assert!(function.at(2.0).approx_eq(&1.0));
+    assert!(function.at(3.0).approx_eq(&1.0));
+}