Adding upstream version 124.0.1.upstream/124.0.1

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

1 files changed, 2222 insertions, 0 deletions

diff --git a/servo/components/style/values/specified/font.rs b/servo/components/style/values/specified/font.rs
new file mode 100644
index 0000000000..2435682ce3
--- /dev/null
+++ b/servo/components/style/values/specified/font.rs
@@ -0,0 +1,2222 @@
+/* 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/. */
+
+//! Specified values for font properties
+
+use crate::context::QuirksMode;
+use crate::parser::{Parse, ParserContext};
+use crate::values::computed::font::{FamilyName, FontFamilyList, SingleFontFamily};
+use crate::values::computed::Percentage as ComputedPercentage;
+use crate::values::computed::{font as computed, Length, NonNegativeLength};
+use crate::values::computed::{CSSPixelLength, Context, ToComputedValue};
+use crate::values::generics::font::{
+    self as generics, FeatureTagValue, FontSettings, FontTag, GenericLineHeight, VariationValue,
+};
+use crate::values::generics::NonNegative;
+use crate::values::specified::length::{FontBaseSize, LineHeightBase, PX_PER_PT};
+use crate::values::specified::{AllowQuirks, Angle, Integer, LengthPercentage};
+use crate::values::specified::{
+    FontRelativeLength, NoCalcLength, NonNegativeLengthPercentage, NonNegativeNumber,
+    NonNegativePercentage, Number,
+};
+use crate::values::{serialize_atom_identifier, CustomIdent, SelectorParseErrorKind};
+use crate::Atom;
+use cssparser::{Parser, Token};
+#[cfg(feature = "gecko")]
+use malloc_size_of::{MallocSizeOf, MallocSizeOfOps, MallocUnconditionalSizeOf};
+use std::fmt::{self, Write};
+use style_traits::values::SequenceWriter;
+use style_traits::{CssWriter, KeywordsCollectFn, ParseError};
+use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
+
+// FIXME(emilio): The system font code is copy-pasta, and should be cleaned up.
+macro_rules! system_font_methods {
+    ($ty:ident, $field:ident) => {
+        system_font_methods!($ty);
+
+        fn compute_system(&self, _context: &Context) -> <$ty as ToComputedValue>::ComputedValue {
+            debug_assert!(matches!(*self, $ty::System(..)));
+            #[cfg(feature = "gecko")]
+            {
+                _context.cached_system_font.as_ref().unwrap().$field.clone()
+            }
+            #[cfg(feature = "servo")]
+            {
+                unreachable!()
+            }
+        }
+    };
+
+    ($ty:ident) => {
+        /// Get a specified value that represents a system font.
+        pub fn system_font(f: SystemFont) -> Self {
+            $ty::System(f)
+        }
+
+        /// Retreive a SystemFont from the specified value.
+        pub fn get_system(&self) -> Option<SystemFont> {
+            if let $ty::System(s) = *self {
+                Some(s)
+            } else {
+                None
+            }
+        }
+    };
+}
+
+/// System fonts.
+#[repr(u8)]
+#[derive(
+    Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+#[allow(missing_docs)]
+pub enum SystemFont {
+    /// https://drafts.csswg.org/css-fonts/#valdef-font-caption
+    Caption,
+    /// https://drafts.csswg.org/css-fonts/#valdef-font-icon
+    Icon,
+    /// https://drafts.csswg.org/css-fonts/#valdef-font-menu
+    Menu,
+    /// https://drafts.csswg.org/css-fonts/#valdef-font-message-box
+    MessageBox,
+    /// https://drafts.csswg.org/css-fonts/#valdef-font-small-caption
+    SmallCaption,
+    /// https://drafts.csswg.org/css-fonts/#valdef-font-status-bar
+    StatusBar,
+    /// Internal system font, used by the `<menupopup>`s on macOS.
+    #[parse(condition = "ParserContext::chrome_rules_enabled")]
+    MozPullDownMenu,
+    /// Internal system font, used for `<button>` elements.
+    #[parse(condition = "ParserContext::chrome_rules_enabled")]
+    MozButton,
+    /// Internal font, used by `<select>` elements.
+    #[parse(condition = "ParserContext::chrome_rules_enabled")]
+    MozList,
+    /// Internal font, used by `<input>` elements.
+    #[parse(condition = "ParserContext::chrome_rules_enabled")]
+    MozField,
+    #[css(skip)]
+    End, // Just for indexing purposes.
+}
+
+const DEFAULT_SCRIPT_MIN_SIZE_PT: u32 = 8;
+const DEFAULT_SCRIPT_SIZE_MULTIPLIER: f64 = 0.71;
+
+/// The minimum font-weight value per:
+///
+/// https://drafts.csswg.org/css-fonts-4/#font-weight-numeric-values
+pub const MIN_FONT_WEIGHT: f32 = 1.;
+
+/// The maximum font-weight value per:
+///
+/// https://drafts.csswg.org/css-fonts-4/#font-weight-numeric-values
+pub const MAX_FONT_WEIGHT: f32 = 1000.;
+
+/// A specified font-weight value.
+///
+/// https://drafts.csswg.org/css-fonts-4/#propdef-font-weight
+#[derive(
+    Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+pub enum FontWeight {
+    /// `<font-weight-absolute>`
+    Absolute(AbsoluteFontWeight),
+    /// Bolder variant
+    Bolder,
+    /// Lighter variant
+    Lighter,
+    /// System font variant.
+    #[css(skip)]
+    System(SystemFont),
+}
+
+impl FontWeight {
+    system_font_methods!(FontWeight, font_weight);
+
+    /// `normal`
+    #[inline]
+    pub fn normal() -> Self {
+        FontWeight::Absolute(AbsoluteFontWeight::Normal)
+    }
+
+    /// Get a specified FontWeight from a gecko keyword
+    pub fn from_gecko_keyword(kw: u32) -> Self {
+        debug_assert!(kw % 100 == 0);
+        debug_assert!(kw as f32 <= MAX_FONT_WEIGHT);
+        FontWeight::Absolute(AbsoluteFontWeight::Weight(Number::new(kw as f32)))
+    }
+}
+
+impl ToComputedValue for FontWeight {
+    type ComputedValue = computed::FontWeight;
+
+    #[inline]
+    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        match *self {
+            FontWeight::Absolute(ref abs) => abs.compute(),
+            FontWeight::Bolder => context
+                .builder
+                .get_parent_font()
+                .clone_font_weight()
+                .bolder(),
+            FontWeight::Lighter => context
+                .builder
+                .get_parent_font()
+                .clone_font_weight()
+                .lighter(),
+            FontWeight::System(_) => self.compute_system(context),
+        }
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &computed::FontWeight) -> Self {
+        FontWeight::Absolute(AbsoluteFontWeight::Weight(Number::from_computed_value(
+            &computed.value(),
+        )))
+    }
+}
+
+/// An absolute font-weight value for a @font-face rule.
+///
+/// https://drafts.csswg.org/css-fonts-4/#font-weight-absolute-values
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+pub enum AbsoluteFontWeight {
+    /// A `<number>`, with the additional constraints specified in:
+    ///
+    ///   https://drafts.csswg.org/css-fonts-4/#font-weight-numeric-values
+    Weight(Number),
+    /// Normal font weight. Same as 400.
+    Normal,
+    /// Bold font weight. Same as 700.
+    Bold,
+}
+
+impl AbsoluteFontWeight {
+    /// Returns the computed value for this absolute font weight.
+    pub fn compute(&self) -> computed::FontWeight {
+        match *self {
+            AbsoluteFontWeight::Weight(weight) => computed::FontWeight::from_float(weight.get()),
+            AbsoluteFontWeight::Normal => computed::FontWeight::NORMAL,
+            AbsoluteFontWeight::Bold => computed::FontWeight::BOLD,
+        }
+    }
+}
+
+impl Parse for AbsoluteFontWeight {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        if let Ok(number) = input.try_parse(|input| Number::parse(context, input)) {
+            // We could add another AllowedNumericType value, but it doesn't
+            // seem worth it just for a single property with such a weird range,
+            // so we do the clamping here manually.
+            if !number.was_calc() &&
+                (number.get() < MIN_FONT_WEIGHT || number.get() > MAX_FONT_WEIGHT)
+            {
+                return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+            }
+            return Ok(AbsoluteFontWeight::Weight(number));
+        }
+
+        Ok(try_match_ident_ignore_ascii_case! { input,
+            "normal" => AbsoluteFontWeight::Normal,
+            "bold" => AbsoluteFontWeight::Bold,
+        })
+    }
+}
+
+/// The specified value of the `font-style` property, without the system font
+/// crap.
+pub type SpecifiedFontStyle = generics::FontStyle<Angle>;
+
+impl ToCss for SpecifiedFontStyle {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        match *self {
+            generics::FontStyle::Normal => dest.write_str("normal"),
+            generics::FontStyle::Italic => dest.write_str("italic"),
+            generics::FontStyle::Oblique(ref angle) => {
+                dest.write_str("oblique")?;
+                if *angle != Self::default_angle() {
+                    dest.write_char(' ')?;
+                    angle.to_css(dest)?;
+                }
+                Ok(())
+            },
+        }
+    }
+}
+
+impl Parse for SpecifiedFontStyle {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Ok(try_match_ident_ignore_ascii_case! { input,
+            "normal" => generics::FontStyle::Normal,
+            "italic" => generics::FontStyle::Italic,
+            "oblique" => {
+                let angle = input.try_parse(|input| Self::parse_angle(context, input))
+                    .unwrap_or_else(|_| Self::default_angle());
+
+                generics::FontStyle::Oblique(angle)
+            },
+        })
+    }
+}
+
+impl ToComputedValue for SpecifiedFontStyle {
+    type ComputedValue = computed::FontStyle;
+
+    fn to_computed_value(&self, _: &Context) -> Self::ComputedValue {
+        match *self {
+            Self::Normal => computed::FontStyle::NORMAL,
+            Self::Italic => computed::FontStyle::ITALIC,
+            Self::Oblique(ref angle) => computed::FontStyle::oblique(angle.degrees()),
+        }
+    }
+
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        if *computed == computed::FontStyle::NORMAL {
+            return Self::Normal;
+        }
+        if *computed == computed::FontStyle::ITALIC {
+            return Self::Italic;
+        }
+        let degrees = computed.oblique_degrees();
+        generics::FontStyle::Oblique(Angle::from_degrees(degrees, /* was_calc = */ false))
+    }
+}
+
+/// From https://drafts.csswg.org/css-fonts-4/#valdef-font-style-oblique-angle:
+///
+///     Values less than -90deg or values greater than 90deg are
+///     invalid and are treated as parse errors.
+///
+/// The maximum angle value that `font-style: oblique` should compute to.
+pub const FONT_STYLE_OBLIQUE_MAX_ANGLE_DEGREES: f32 = 90.;
+
+/// The minimum angle value that `font-style: oblique` should compute to.
+pub const FONT_STYLE_OBLIQUE_MIN_ANGLE_DEGREES: f32 = -90.;
+
+impl SpecifiedFontStyle {
+    /// Gets a clamped angle in degrees from a specified Angle.
+    pub fn compute_angle_degrees(angle: &Angle) -> f32 {
+        angle
+            .degrees()
+            .max(FONT_STYLE_OBLIQUE_MIN_ANGLE_DEGREES)
+            .min(FONT_STYLE_OBLIQUE_MAX_ANGLE_DEGREES)
+    }
+
+    /// Parse a suitable angle for font-style: oblique.
+    pub fn parse_angle<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Angle, ParseError<'i>> {
+        let angle = Angle::parse(context, input)?;
+        if angle.was_calc() {
+            return Ok(angle);
+        }
+
+        let degrees = angle.degrees();
+        if degrees < FONT_STYLE_OBLIQUE_MIN_ANGLE_DEGREES ||
+            degrees > FONT_STYLE_OBLIQUE_MAX_ANGLE_DEGREES
+        {
+            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+        }
+        return Ok(angle);
+    }
+
+    /// The default angle for `font-style: oblique`.
+    pub fn default_angle() -> Angle {
+        Angle::from_degrees(
+            computed::FontStyle::DEFAULT_OBLIQUE_DEGREES as f32,
+            /* was_calc = */ false,
+        )
+    }
+}
+
+/// The specified value of the `font-style` property.
+#[derive(
+    Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+#[allow(missing_docs)]
+pub enum FontStyle {
+    Specified(SpecifiedFontStyle),
+    #[css(skip)]
+    System(SystemFont),
+}
+
+impl FontStyle {
+    /// Return the `normal` value.
+    #[inline]
+    pub fn normal() -> Self {
+        FontStyle::Specified(generics::FontStyle::Normal)
+    }
+
+    system_font_methods!(FontStyle, font_style);
+}
+
+impl ToComputedValue for FontStyle {
+    type ComputedValue = computed::FontStyle;
+
+    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        match *self {
+            FontStyle::Specified(ref specified) => specified.to_computed_value(context),
+            FontStyle::System(..) => self.compute_system(context),
+        }
+    }
+
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        FontStyle::Specified(SpecifiedFontStyle::from_computed_value(computed))
+    }
+}
+
+/// A value for the `font-stretch` property.
+///
+/// https://drafts.csswg.org/css-fonts-4/#font-stretch-prop
+#[allow(missing_docs)]
+#[derive(
+    Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+pub enum FontStretch {
+    Stretch(NonNegativePercentage),
+    Keyword(FontStretchKeyword),
+    #[css(skip)]
+    System(SystemFont),
+}
+
+/// A keyword value for `font-stretch`.
+#[derive(
+    Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+#[allow(missing_docs)]
+pub enum FontStretchKeyword {
+    Normal,
+    Condensed,
+    UltraCondensed,
+    ExtraCondensed,
+    SemiCondensed,
+    SemiExpanded,
+    Expanded,
+    ExtraExpanded,
+    UltraExpanded,
+}
+
+impl FontStretchKeyword {
+    /// Turns the keyword into a computed value.
+    pub fn compute(&self) -> computed::FontStretch {
+        computed::FontStretch::from_keyword(*self)
+    }
+
+    /// Does the opposite operation to `compute`, in order to serialize keywords
+    /// if possible.
+    pub fn from_percentage(p: f32) -> Option<Self> {
+        computed::FontStretch::from_percentage(p).as_keyword()
+    }
+}
+
+impl FontStretch {
+    /// `normal`.
+    pub fn normal() -> Self {
+        FontStretch::Keyword(FontStretchKeyword::Normal)
+    }
+
+    system_font_methods!(FontStretch, font_stretch);
+}
+
+impl ToComputedValue for FontStretch {
+    type ComputedValue = computed::FontStretch;
+
+    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        match *self {
+            FontStretch::Stretch(ref percentage) => {
+                let percentage = percentage.to_computed_value(context).0;
+                computed::FontStretch::from_percentage(percentage.0)
+            },
+            FontStretch::Keyword(ref kw) => kw.compute(),
+            FontStretch::System(_) => self.compute_system(context),
+        }
+    }
+
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        FontStretch::Stretch(NonNegativePercentage::from_computed_value(&NonNegative(
+            computed.to_percentage(),
+        )))
+    }
+}
+
+#[cfg(feature = "gecko")]
+fn math_depth_enabled(_context: &ParserContext) -> bool {
+    static_prefs::pref!("layout.css.math-depth.enabled")
+}
+
+#[cfg(feature = "servo")]
+fn math_depth_enabled(_context: &ParserContext) -> bool {
+    false
+}
+
+/// CSS font keywords
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+    Serialize,
+    Deserialize,
+)]
+#[allow(missing_docs)]
+#[repr(u8)]
+pub enum FontSizeKeyword {
+    #[css(keyword = "xx-small")]
+    XXSmall,
+    XSmall,
+    Small,
+    Medium,
+    Large,
+    XLarge,
+    #[css(keyword = "xx-large")]
+    XXLarge,
+    #[css(keyword = "xxx-large")]
+    XXXLarge,
+    /// Indicate whether to apply font-size: math is specified so that extra
+    /// scaling due to math-depth changes is applied during the cascade.
+    #[parse(condition = "math_depth_enabled")]
+    Math,
+    #[css(skip)]
+    None,
+}
+
+impl FontSizeKeyword {
+    /// Convert to an HTML <font size> value
+    #[inline]
+    pub fn html_size(self) -> u8 {
+        self as u8
+    }
+}
+
+impl Default for FontSizeKeyword {
+    fn default() -> Self {
+        FontSizeKeyword::Medium
+    }
+}
+
+#[derive(
+    Animate,
+    Clone,
+    ComputeSquaredDistance,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    ToAnimatedValue,
+    ToAnimatedZero,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[cfg_attr(feature = "servo", derive(Serialize, Deserialize))]
+/// Additional information for keyword-derived font sizes.
+pub struct KeywordInfo {
+    /// The keyword used
+    pub kw: FontSizeKeyword,
+    /// A factor to be multiplied by the computed size of the keyword
+    #[css(skip)]
+    pub factor: f32,
+    /// An additional fixed offset to add to the kw * factor in the case of
+    /// `calc()`.
+    #[css(skip)]
+    pub offset: CSSPixelLength,
+}
+
+impl KeywordInfo {
+    /// KeywordInfo value for font-size: medium
+    pub fn medium() -> Self {
+        Self::new(FontSizeKeyword::Medium)
+    }
+
+    /// KeywordInfo value for font-size: none
+    pub fn none() -> Self {
+        Self::new(FontSizeKeyword::None)
+    }
+
+    fn new(kw: FontSizeKeyword) -> Self {
+        KeywordInfo {
+            kw,
+            factor: 1.,
+            offset: CSSPixelLength::new(0.),
+        }
+    }
+
+    /// Computes the final size for this font-size keyword, accounting for
+    /// text-zoom.
+    fn to_computed_value(&self, context: &Context) -> CSSPixelLength {
+        debug_assert_ne!(self.kw, FontSizeKeyword::None);
+        debug_assert_ne!(self.kw, FontSizeKeyword::Math);
+        let base = context.maybe_zoom_text(self.kw.to_length(context).0);
+        base * self.factor + context.maybe_zoom_text(self.offset)
+    }
+
+    /// Given a parent keyword info (self), apply an additional factor/offset to
+    /// it.
+    fn compose(self, factor: f32) -> Self {
+        if self.kw == FontSizeKeyword::None {
+            return self;
+        }
+        KeywordInfo {
+            kw: self.kw,
+            factor: self.factor * factor,
+            offset: self.offset * factor,
+        }
+    }
+}
+
+impl SpecifiedValueInfo for KeywordInfo {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        <FontSizeKeyword as SpecifiedValueInfo>::collect_completion_keywords(f);
+    }
+}
+
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+/// A specified font-size value
+pub enum FontSize {
+    /// A length; e.g. 10px.
+    Length(LengthPercentage),
+    /// A keyword value, along with a ratio and absolute offset.
+    /// The ratio in any specified keyword value
+    /// will be 1 (with offset 0), but we cascade keywordness even
+    /// after font-relative (percent and em) values
+    /// have been applied, which is where the ratio
+    /// comes in. The offset comes in if we cascaded a calc value,
+    /// where the font-relative portion (em and percentage) will
+    /// go into the ratio, and the remaining units all computed together
+    /// will go into the offset.
+    /// See bug 1355707.
+    Keyword(KeywordInfo),
+    /// font-size: smaller
+    Smaller,
+    /// font-size: larger
+    Larger,
+    /// Derived from a specified system font.
+    #[css(skip)]
+    System(SystemFont),
+}
+
+/// Specifies a prioritized list of font family names or generic family names.
+#[derive(Clone, Debug, Eq, PartialEq, ToCss, ToShmem)]
+#[cfg_attr(feature = "servo", derive(Hash))]
+pub enum FontFamily {
+    /// List of `font-family`
+    #[css(comma)]
+    Values(#[css(iterable)] FontFamilyList),
+    /// System font
+    #[css(skip)]
+    System(SystemFont),
+}
+
+impl FontFamily {
+    system_font_methods!(FontFamily, font_family);
+}
+
+impl ToComputedValue for FontFamily {
+    type ComputedValue = computed::FontFamily;
+
+    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        match *self {
+            FontFamily::Values(ref list) => computed::FontFamily {
+                families: list.clone(),
+                is_system_font: false,
+                is_initial: false,
+            },
+            FontFamily::System(_) => self.compute_system(context),
+        }
+    }
+
+    fn from_computed_value(other: &computed::FontFamily) -> Self {
+        FontFamily::Values(other.families.clone())
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl MallocSizeOf for FontFamily {
+    fn size_of(&self, ops: &mut MallocSizeOfOps) -> usize {
+        match *self {
+            FontFamily::Values(ref v) => {
+                // Although the family list is refcounted, we always attribute
+                // its size to the specified value.
+                v.list.unconditional_size_of(ops)
+            },
+            FontFamily::System(_) => 0,
+        }
+    }
+}
+
+impl Parse for FontFamily {
+    /// <family-name>#
+    /// <family-name> = <string> | [ <ident>+ ]
+    /// TODO: <generic-family>
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<FontFamily, ParseError<'i>> {
+        let values =
+            input.parse_comma_separated(|input| SingleFontFamily::parse(context, input))?;
+        Ok(FontFamily::Values(FontFamilyList {
+            list: crate::ArcSlice::from_iter(values.into_iter()),
+        }))
+    }
+}
+
+impl SpecifiedValueInfo for FontFamily {}
+
+/// `FamilyName::parse` is based on `SingleFontFamily::parse` and not the other
+/// way around because we want the former to exclude generic family keywords.
+impl Parse for FamilyName {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        match SingleFontFamily::parse(context, input) {
+            Ok(SingleFontFamily::FamilyName(name)) => Ok(name),
+            Ok(SingleFontFamily::Generic(_)) => {
+                Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+            },
+            Err(e) => Err(e),
+        }
+    }
+}
+
+/// A factor for one of the font-size-adjust metrics, which may be either a number
+/// or the `from-font` keyword.
+#[derive(
+    Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+pub enum FontSizeAdjustFactor {
+    /// An explicitly-specified number.
+    Number(NonNegativeNumber),
+    /// The from-font keyword: resolve the number from font metrics.
+    FromFont,
+}
+
+/// Specified value for font-size-adjust, intended to help
+/// preserve the readability of text when font fallback occurs.
+///
+/// https://drafts.csswg.org/css-fonts-5/#font-size-adjust-prop
+pub type FontSizeAdjust = generics::GenericFontSizeAdjust<FontSizeAdjustFactor>;
+
+impl Parse for FontSizeAdjust {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        // First check if we have an adjustment factor without a metrics-basis keyword.
+        if let Ok(factor) = input.try_parse(|i| FontSizeAdjustFactor::parse(context, i)) {
+            return Ok(Self::ExHeight(factor));
+        }
+
+        let ident = input.expect_ident()?;
+        let basis = match_ignore_ascii_case! { &ident,
+            "none" => return Ok(Self::None),
+            // Check for size adjustment basis keywords.
+            "ex-height" => Self::ExHeight,
+            "cap-height" => Self::CapHeight,
+            "ch-width" => Self::ChWidth,
+            "ic-width" => Self::IcWidth,
+            "ic-height" => Self::IcHeight,
+            // Unknown keyword.
+            _ => return Err(location.new_custom_error(
+                SelectorParseErrorKind::UnexpectedIdent(ident.clone())
+            )),
+        };
+
+        Ok(basis(FontSizeAdjustFactor::parse(context, input)?))
+    }
+}
+
+/// This is the ratio applied for font-size: larger
+/// and smaller by both Firefox and Chrome
+const LARGER_FONT_SIZE_RATIO: f32 = 1.2;
+
+/// The default font size.
+pub const FONT_MEDIUM_PX: f32 = 16.0;
+/// The default line height.
+pub const FONT_MEDIUM_LINE_HEIGHT_PX: f32 = FONT_MEDIUM_PX * 1.2;
+
+impl FontSizeKeyword {
+    #[inline]
+    #[cfg(feature = "servo")]
+    fn to_length(&self, _: &Context) -> NonNegativeLength {
+        let medium = Length::new(FONT_MEDIUM_PX);
+        // https://drafts.csswg.org/css-fonts-3/#font-size-prop
+        NonNegative(match *self {
+            FontSizeKeyword::XXSmall => medium * 3.0 / 5.0,
+            FontSizeKeyword::XSmall => medium * 3.0 / 4.0,
+            FontSizeKeyword::Small => medium * 8.0 / 9.0,
+            FontSizeKeyword::Medium => medium,
+            FontSizeKeyword::Large => medium * 6.0 / 5.0,
+            FontSizeKeyword::XLarge => medium * 3.0 / 2.0,
+            FontSizeKeyword::XXLarge => medium * 2.0,
+            FontSizeKeyword::XXXLarge => medium * 3.0,
+            FontSizeKeyword::Math | FontSizeKeyword::None => unreachable!(),
+        })
+    }
+
+    #[cfg(feature = "gecko")]
+    #[inline]
+    fn to_length(&self, cx: &Context) -> NonNegativeLength {
+        let font = cx.style().get_font();
+        let family = &font.mFont.family.families;
+        let generic = family
+            .single_generic()
+            .unwrap_or(computed::GenericFontFamily::None);
+        let base_size = unsafe {
+            Atom::with(font.mLanguage.mRawPtr, |language| {
+                cx.device().base_size_for_generic(language, generic)
+            })
+        };
+        self.to_length_without_context(cx.quirks_mode, base_size)
+    }
+
+    /// Resolve a keyword length without any context, with explicit arguments.
+    #[cfg(feature = "gecko")]
+    #[inline]
+    pub fn to_length_without_context(
+        &self,
+        quirks_mode: QuirksMode,
+        base_size: Length,
+    ) -> NonNegativeLength {
+        debug_assert_ne!(*self, FontSizeKeyword::Math);
+        // The tables in this function are originally from
+        // nsRuleNode::CalcFontPointSize in Gecko:
+        //
+        // https://searchfox.org/mozilla-central/rev/c05d9d61188d32b8/layout/style/nsRuleNode.cpp#3150
+        //
+        // Mapping from base size and HTML size to pixels
+        // The first index is (base_size - 9), the second is the
+        // HTML size. "0" is CSS keyword xx-small, not HTML size 0,
+        // since HTML size 0 is the same as 1.
+        //
+        //  xxs   xs      s      m     l      xl     xxl   -
+        //  -     0/1     2      3     4      5      6     7
+        static FONT_SIZE_MAPPING: [[i32; 8]; 8] = [
+            [9, 9, 9, 9, 11, 14, 18, 27],
+            [9, 9, 9, 10, 12, 15, 20, 30],
+            [9, 9, 10, 11, 13, 17, 22, 33],
+            [9, 9, 10, 12, 14, 18, 24, 36],
+            [9, 10, 12, 13, 16, 20, 26, 39],
+            [9, 10, 12, 14, 17, 21, 28, 42],
+            [9, 10, 13, 15, 18, 23, 30, 45],
+            [9, 10, 13, 16, 18, 24, 32, 48],
+        ];
+
+        // This table gives us compatibility with WinNav4 for the default fonts only.
+        // In WinNav4, the default fonts were:
+        //
+        //     Times/12pt ==   Times/16px at 96ppi
+        //   Courier/10pt == Courier/13px at 96ppi
+        //
+        // xxs   xs     s      m      l     xl     xxl    -
+        // -     1      2      3      4     5      6      7
+        static QUIRKS_FONT_SIZE_MAPPING: [[i32; 8]; 8] = [
+            [9, 9, 9, 9, 11, 14, 18, 28],
+            [9, 9, 9, 10, 12, 15, 20, 31],
+            [9, 9, 9, 11, 13, 17, 22, 34],
+            [9, 9, 10, 12, 14, 18, 24, 37],
+            [9, 9, 10, 13, 16, 20, 26, 40],
+            [9, 9, 11, 14, 17, 21, 28, 42],
+            [9, 10, 12, 15, 17, 23, 30, 45],
+            [9, 10, 13, 16, 18, 24, 32, 48],
+        ];
+
+        static FONT_SIZE_FACTORS: [i32; 8] = [60, 75, 89, 100, 120, 150, 200, 300];
+        let base_size_px = base_size.px().round() as i32;
+        let html_size = self.html_size() as usize;
+        NonNegative(if base_size_px >= 9 && base_size_px <= 16 {
+            let mapping = if quirks_mode == QuirksMode::Quirks {
+                QUIRKS_FONT_SIZE_MAPPING
+            } else {
+                FONT_SIZE_MAPPING
+            };
+            Length::new(mapping[(base_size_px - 9) as usize][html_size] as f32)
+        } else {
+            base_size * FONT_SIZE_FACTORS[html_size] as f32 / 100.0
+        })
+    }
+}
+
+impl FontSize {
+    /// <https://html.spec.whatwg.org/multipage/#rules-for-parsing-a-legacy-font-size>
+    pub fn from_html_size(size: u8) -> Self {
+        FontSize::Keyword(KeywordInfo::new(match size {
+            // If value is less than 1, let it be 1.
+            0 | 1 => FontSizeKeyword::XSmall,
+            2 => FontSizeKeyword::Small,
+            3 => FontSizeKeyword::Medium,
+            4 => FontSizeKeyword::Large,
+            5 => FontSizeKeyword::XLarge,
+            6 => FontSizeKeyword::XXLarge,
+            // If value is greater than 7, let it be 7.
+            _ => FontSizeKeyword::XXXLarge,
+        }))
+    }
+
+    /// Compute it against a given base font size
+    pub fn to_computed_value_against(
+        &self,
+        context: &Context,
+        base_size: FontBaseSize,
+        line_height_base: LineHeightBase,
+    ) -> computed::FontSize {
+        let compose_keyword = |factor| {
+            context
+                .style()
+                .get_parent_font()
+                .clone_font_size()
+                .keyword_info
+                .compose(factor)
+        };
+        let mut info = KeywordInfo::none();
+        let size = match *self {
+            FontSize::Length(LengthPercentage::Length(ref l)) => {
+                if let NoCalcLength::FontRelative(ref value) = *l {
+                    if let FontRelativeLength::Em(em) = *value {
+                        // If the parent font was keyword-derived, this is
+                        // too. Tack the em unit onto the factor
+                        info = compose_keyword(em);
+                    }
+                }
+                let result =
+                    l.to_computed_value_with_base_size(context, base_size, line_height_base);
+                if l.should_zoom_text() {
+                    context.maybe_zoom_text(result)
+                } else {
+                    result
+                }
+            },
+            FontSize::Length(LengthPercentage::Percentage(pc)) => {
+                // If the parent font was keyword-derived, this is too.
+                // Tack the % onto the factor
+                info = compose_keyword(pc.0);
+                (base_size.resolve(context).computed_size() * pc.0).normalized()
+            },
+            FontSize::Length(LengthPercentage::Calc(ref calc)) => {
+                let calc = calc.to_computed_value_zoomed(context, base_size, line_height_base);
+                calc.resolve(base_size.resolve(context).computed_size())
+            },
+            FontSize::Keyword(i) => {
+                if i.kw == FontSizeKeyword::Math {
+                    // Scaling is done in recompute_math_font_size_if_needed().
+                    info = compose_keyword(1.);
+                    info.kw = FontSizeKeyword::Math;
+                    FontRelativeLength::Em(1.).to_computed_value(
+                        context,
+                        base_size,
+                        line_height_base,
+                    )
+                } else {
+                    // As a specified keyword, this is keyword derived
+                    info = i;
+                    i.to_computed_value(context).clamp_to_non_negative()
+                }
+            },
+            FontSize::Smaller => {
+                info = compose_keyword(1. / LARGER_FONT_SIZE_RATIO);
+                FontRelativeLength::Em(1. / LARGER_FONT_SIZE_RATIO).to_computed_value(
+                    context,
+                    base_size,
+                    line_height_base,
+                )
+            },
+            FontSize::Larger => {
+                info = compose_keyword(LARGER_FONT_SIZE_RATIO);
+                FontRelativeLength::Em(LARGER_FONT_SIZE_RATIO).to_computed_value(
+                    context,
+                    base_size,
+                    line_height_base,
+                )
+            },
+
+            FontSize::System(_) => {
+                #[cfg(feature = "servo")]
+                {
+                    unreachable!()
+                }
+                #[cfg(feature = "gecko")]
+                {
+                    context
+                        .cached_system_font
+                        .as_ref()
+                        .unwrap()
+                        .font_size
+                        .computed_size()
+                }
+            },
+        };
+        computed::FontSize {
+            computed_size: NonNegative(size),
+            used_size: NonNegative(size),
+            keyword_info: info,
+        }
+    }
+}
+
+impl ToComputedValue for FontSize {
+    type ComputedValue = computed::FontSize;
+
+    #[inline]
+    fn to_computed_value(&self, context: &Context) -> computed::FontSize {
+        self.to_computed_value_against(
+            context,
+            FontBaseSize::InheritedStyle,
+            LineHeightBase::InheritedStyle,
+        )
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &computed::FontSize) -> Self {
+        FontSize::Length(LengthPercentage::Length(
+            ToComputedValue::from_computed_value(&computed.computed_size()),
+        ))
+    }
+}
+
+impl FontSize {
+    system_font_methods!(FontSize);
+
+    /// Get initial value for specified font size.
+    #[inline]
+    pub fn medium() -> Self {
+        FontSize::Keyword(KeywordInfo::medium())
+    }
+
+    /// Parses a font-size, with quirks.
+    pub fn parse_quirky<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+        allow_quirks: AllowQuirks,
+    ) -> Result<FontSize, ParseError<'i>> {
+        if let Ok(lp) = input
+            .try_parse(|i| LengthPercentage::parse_non_negative_quirky(context, i, allow_quirks))
+        {
+            return Ok(FontSize::Length(lp));
+        }
+
+        if let Ok(kw) = input.try_parse(|i| FontSizeKeyword::parse(context, i)) {
+            return Ok(FontSize::Keyword(KeywordInfo::new(kw)));
+        }
+
+        try_match_ident_ignore_ascii_case! { input,
+            "smaller" => Ok(FontSize::Smaller),
+            "larger" => Ok(FontSize::Larger),
+        }
+    }
+}
+
+impl Parse for FontSize {
+    /// <length> | <percentage> | <absolute-size> | <relative-size>
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<FontSize, ParseError<'i>> {
+        FontSize::parse_quirky(context, input, AllowQuirks::No)
+    }
+}
+
+bitflags! {
+    #[derive(Clone, Copy)]
+    /// Flags of variant alternates in bit
+    struct VariantAlternatesParsingFlags: u8 {
+        /// None of variant alternates enabled
+        const NORMAL = 0;
+        /// Historical forms
+        const HISTORICAL_FORMS = 0x01;
+        /// Stylistic Alternates
+        const STYLISTIC = 0x02;
+        /// Stylistic Sets
+        const STYLESET = 0x04;
+        /// Character Variant
+        const CHARACTER_VARIANT = 0x08;
+        /// Swash glyphs
+        const SWASH = 0x10;
+        /// Ornaments glyphs
+        const ORNAMENTS = 0x20;
+        /// Annotation forms
+        const ANNOTATION = 0x40;
+    }
+}
+
+#[derive(
+    Clone,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToCss,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C, u8)]
+/// Set of variant alternates
+pub enum VariantAlternates {
+    /// Enables display of stylistic alternates
+    #[css(function)]
+    Stylistic(CustomIdent),
+    /// Enables display with stylistic sets
+    #[css(comma, function)]
+    Styleset(#[css(iterable)] crate::OwnedSlice<CustomIdent>),
+    /// Enables display of specific character variants
+    #[css(comma, function)]
+    CharacterVariant(#[css(iterable)] crate::OwnedSlice<CustomIdent>),
+    /// Enables display of swash glyphs
+    #[css(function)]
+    Swash(CustomIdent),
+    /// Enables replacement of default glyphs with ornaments
+    #[css(function)]
+    Ornaments(CustomIdent),
+    /// Enables display of alternate annotation forms
+    #[css(function)]
+    Annotation(CustomIdent),
+    /// Enables display of historical forms
+    HistoricalForms,
+}
+
+#[derive(
+    Clone,
+    Debug,
+    Default,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(transparent)]
+/// List of Variant Alternates
+pub struct FontVariantAlternates(
+    #[css(if_empty = "normal", iterable)] crate::OwnedSlice<VariantAlternates>,
+);
+
+impl FontVariantAlternates {
+    /// Returns the length of all variant alternates.
+    pub fn len(&self) -> usize {
+        self.0.iter().fold(0, |acc, alternate| match *alternate {
+            VariantAlternates::Swash(_) |
+            VariantAlternates::Stylistic(_) |
+            VariantAlternates::Ornaments(_) |
+            VariantAlternates::Annotation(_) => acc + 1,
+            VariantAlternates::Styleset(ref slice) |
+            VariantAlternates::CharacterVariant(ref slice) => acc + slice.len(),
+            _ => acc,
+        })
+    }
+}
+
+impl FontVariantAlternates {
+    #[inline]
+    /// Get initial specified value with VariantAlternatesList
+    pub fn get_initial_specified_value() -> Self {
+        Default::default()
+    }
+}
+
+impl Parse for FontVariantAlternates {
+    /// normal |
+    ///  [ stylistic(<feature-value-name>)           ||
+    ///    historical-forms                          ||
+    ///    styleset(<feature-value-name> #)          ||
+    ///    character-variant(<feature-value-name> #) ||
+    ///    swash(<feature-value-name>)               ||
+    ///    ornaments(<feature-value-name>)           ||
+    ///    annotation(<feature-value-name>) ]
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<FontVariantAlternates, ParseError<'i>> {
+        if input
+            .try_parse(|input| input.expect_ident_matching("normal"))
+            .is_ok()
+        {
+            return Ok(Default::default());
+        }
+
+        let mut stylistic = None;
+        let mut historical = None;
+        let mut styleset = None;
+        let mut character_variant = None;
+        let mut swash = None;
+        let mut ornaments = None;
+        let mut annotation = None;
+
+        // Parse values for the various alternate types in any order.
+        let mut parsed_alternates = VariantAlternatesParsingFlags::empty();
+        macro_rules! check_if_parsed(
+            ($input:expr, $flag:path) => (
+                if parsed_alternates.contains($flag) {
+                    return Err($input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+                }
+                parsed_alternates |= $flag;
+            )
+        );
+        while let Ok(_) = input.try_parse(|input| match *input.next()? {
+            Token::Ident(ref value) if value.eq_ignore_ascii_case("historical-forms") => {
+                check_if_parsed!(input, VariantAlternatesParsingFlags::HISTORICAL_FORMS);
+                historical = Some(VariantAlternates::HistoricalForms);
+                Ok(())
+            },
+            Token::Function(ref name) => {
+                let name = name.clone();
+                input.parse_nested_block(|i| {
+                    match_ignore_ascii_case! { &name,
+                        "swash" => {
+                            check_if_parsed!(i, VariantAlternatesParsingFlags::SWASH);
+                            let ident = CustomIdent::parse(i, &[])?;
+                            swash = Some(VariantAlternates::Swash(ident));
+                            Ok(())
+                        },
+                        "stylistic" => {
+                            check_if_parsed!(i, VariantAlternatesParsingFlags::STYLISTIC);
+                            let ident = CustomIdent::parse(i, &[])?;
+                            stylistic = Some(VariantAlternates::Stylistic(ident));
+                            Ok(())
+                        },
+                        "ornaments" => {
+                            check_if_parsed!(i, VariantAlternatesParsingFlags::ORNAMENTS);
+                            let ident = CustomIdent::parse(i, &[])?;
+                            ornaments = Some(VariantAlternates::Ornaments(ident));
+                            Ok(())
+                        },
+                        "annotation" => {
+                            check_if_parsed!(i, VariantAlternatesParsingFlags::ANNOTATION);
+                            let ident = CustomIdent::parse(i, &[])?;
+                            annotation = Some(VariantAlternates::Annotation(ident));
+                            Ok(())
+                        },
+                        "styleset" => {
+                            check_if_parsed!(i, VariantAlternatesParsingFlags::STYLESET);
+                            let idents = i.parse_comma_separated(|i| {
+                                CustomIdent::parse(i, &[])
+                            })?;
+                            styleset = Some(VariantAlternates::Styleset(idents.into()));
+                            Ok(())
+                        },
+                        "character-variant" => {
+                            check_if_parsed!(i, VariantAlternatesParsingFlags::CHARACTER_VARIANT);
+                            let idents = i.parse_comma_separated(|i| {
+                                CustomIdent::parse(i, &[])
+                            })?;
+                            character_variant = Some(VariantAlternates::CharacterVariant(idents.into()));
+                            Ok(())
+                        },
+                        _ => return Err(i.new_custom_error(StyleParseErrorKind::UnspecifiedError)),
+                    }
+                })
+            },
+            _ => Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError)),
+        }) {}
+
+        if parsed_alternates.is_empty() {
+            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+        }
+
+        // Collect the parsed values in canonical order, so that we'll serialize correctly.
+        let mut alternates = Vec::new();
+        macro_rules! push_if_some(
+            ($value:expr) => (
+                if let Some(v) = $value {
+                    alternates.push(v);
+                }
+            )
+        );
+        push_if_some!(stylistic);
+        push_if_some!(historical);
+        push_if_some!(styleset);
+        push_if_some!(character_variant);
+        push_if_some!(swash);
+        push_if_some!(ornaments);
+        push_if_some!(annotation);
+
+        Ok(FontVariantAlternates(alternates.into()))
+    }
+}
+
+macro_rules! impl_variant_east_asian {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $gecko:ident = $value:expr,
+        )+
+    } => {
+        #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToResolvedValue, ToShmem)]
+        /// Variants for east asian variant
+        pub struct FontVariantEastAsian(u16);
+        bitflags! {
+            impl FontVariantEastAsian: u16 {
+                /// None of the features
+                const NORMAL = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+            }
+        }
+
+        impl ToCss for FontVariantEastAsian {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("normal");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.intersects(Self::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
+        #[cfg(feature = "gecko")]
+        #[inline]
+        pub fn assert_variant_east_asian_matches() {
+            use crate::gecko_bindings::structs;
+            $(
+                debug_assert_eq!(structs::$gecko as u16, FontVariantEastAsian::$ident.bits());
+            )+
+        }
+
+        impl SpecifiedValueInfo for FontVariantEastAsian {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["normal", $($css,)+]);
+            }
+        }
+    }
+}
+
+impl_variant_east_asian! {
+    /// Enables rendering of JIS78 forms (OpenType feature: jp78)
+    JIS78 / "jis78" => NS_FONT_VARIANT_EAST_ASIAN_JIS78 = 0x01,
+    /// Enables rendering of JIS83 forms (OpenType feature: jp83).
+    JIS83 / "jis83" => NS_FONT_VARIANT_EAST_ASIAN_JIS83 = 0x02,
+    /// Enables rendering of JIS90 forms (OpenType feature: jp90).
+    JIS90 / "jis90" => NS_FONT_VARIANT_EAST_ASIAN_JIS90 = 0x04,
+    /// Enables rendering of JIS2004 forms (OpenType feature: jp04).
+    JIS04 / "jis04" => NS_FONT_VARIANT_EAST_ASIAN_JIS04 = 0x08,
+    /// Enables rendering of simplified forms (OpenType feature: smpl).
+    SIMPLIFIED / "simplified" => NS_FONT_VARIANT_EAST_ASIAN_SIMPLIFIED = 0x10,
+    /// Enables rendering of traditional forms (OpenType feature: trad).
+    TRADITIONAL / "traditional" => NS_FONT_VARIANT_EAST_ASIAN_TRADITIONAL = 0x20,
+    /// Enables rendering of full-width variants (OpenType feature: fwid).
+    FULL_WIDTH / "full-width" => NS_FONT_VARIANT_EAST_ASIAN_FULL_WIDTH = 0x40,
+    /// Enables rendering of proportionally-spaced variants (OpenType feature: pwid).
+    PROPORTIONAL_WIDTH / "proportional-width" => NS_FONT_VARIANT_EAST_ASIAN_PROP_WIDTH = 0x80,
+    /// Enables display of ruby variant glyphs (OpenType feature: ruby).
+    RUBY / "ruby" => NS_FONT_VARIANT_EAST_ASIAN_RUBY = 0x100,
+}
+
+#[cfg(feature = "gecko")]
+impl FontVariantEastAsian {
+    /// Obtain a specified value from a Gecko keyword value
+    ///
+    /// Intended for use with presentation attributes, not style structs
+    pub fn from_gecko_keyword(kw: u16) -> Self {
+        Self::from_bits_truncate(kw)
+    }
+
+    /// Transform into gecko keyword
+    pub fn to_gecko_keyword(self) -> u16 {
+        self.bits()
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl_gecko_keyword_conversions!(FontVariantEastAsian, u16);
+
+impl Parse for FontVariantEastAsian {
+    /// normal | [ <east-asian-variant-values> || <east-asian-width-values> || ruby ]
+    /// <east-asian-variant-values> = [ jis78 | jis83 | jis90 | jis04 | simplified | traditional ]
+    /// <east-asian-width-values>   = [ full-width | proportional-width ]
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let mut result = Self::empty();
+
+        if input
+            .try_parse(|input| input.expect_ident_matching("normal"))
+            .is_ok()
+        {
+            return Ok(result);
+        }
+
+        while let Ok(flag) = input.try_parse(|input| {
+            Ok(
+                match_ignore_ascii_case! { &input.expect_ident().map_err(|_| ())?,
+                    "jis78" =>
+                        exclusive_value!((result, Self::JIS78 | Self::JIS83 |
+                                                  Self::JIS90 | Self::JIS04 |
+                                                  Self::SIMPLIFIED | Self::TRADITIONAL
+                                        ) => Self::JIS78),
+                    "jis83" =>
+                        exclusive_value!((result, Self::JIS78 | Self::JIS83 |
+                                                  Self::JIS90 | Self::JIS04 |
+                                                  Self::SIMPLIFIED | Self::TRADITIONAL
+                                        ) => Self::JIS83),
+                    "jis90" =>
+                        exclusive_value!((result, Self::JIS78 | Self::JIS83 |
+                                                  Self::JIS90 | Self::JIS04 |
+                                                  Self::SIMPLIFIED | Self::TRADITIONAL
+                                        ) => Self::JIS90),
+                    "jis04" =>
+                        exclusive_value!((result, Self::JIS78 | Self::JIS83 |
+                                                  Self::JIS90 | Self::JIS04 |
+                                                  Self::SIMPLIFIED | Self::TRADITIONAL
+                                        ) => Self::JIS04),
+                    "simplified" =>
+                        exclusive_value!((result, Self::JIS78 | Self::JIS83 |
+                                                  Self::JIS90 | Self::JIS04 |
+                                                  Self::SIMPLIFIED | Self::TRADITIONAL
+                                        ) => Self::SIMPLIFIED),
+                    "traditional" =>
+                        exclusive_value!((result, Self::JIS78 | Self::JIS83 |
+                                                  Self::JIS90 | Self::JIS04 |
+                                                  Self::SIMPLIFIED | Self::TRADITIONAL
+                                        ) => Self::TRADITIONAL),
+                    "full-width" =>
+                        exclusive_value!((result, Self::FULL_WIDTH |
+                                                  Self::PROPORTIONAL_WIDTH
+                                        ) => Self::FULL_WIDTH),
+                    "proportional-width" =>
+                        exclusive_value!((result, Self::FULL_WIDTH |
+                                                  Self::PROPORTIONAL_WIDTH
+                                        ) => Self::PROPORTIONAL_WIDTH),
+                    "ruby" =>
+                        exclusive_value!((result, Self::RUBY) => Self::RUBY),
+                    _ => return Err(()),
+                },
+            )
+        }) {
+            result.insert(flag);
+        }
+
+        if !result.is_empty() {
+            Ok(result)
+        } else {
+            Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+        }
+    }
+}
+
+macro_rules! impl_variant_ligatures {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $gecko:ident = $value:expr,
+        )+
+    } => {
+        #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToResolvedValue, ToShmem)]
+        /// Variants of ligatures
+        pub struct FontVariantLigatures(u16);
+        bitflags! {
+            impl FontVariantLigatures: u16 {
+                /// Specifies that common default features are enabled
+                const NORMAL = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+            }
+        }
+
+        impl ToCss for FontVariantLigatures {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("normal");
+                }
+                if self.contains(FontVariantLigatures::NONE) {
+                    return dest.write_str("none");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.intersects(FontVariantLigatures::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
+        #[cfg(feature = "gecko")]
+        #[inline]
+        pub fn assert_variant_ligatures_matches() {
+            use crate::gecko_bindings::structs;
+            $(
+                debug_assert_eq!(structs::$gecko as u16, FontVariantLigatures::$ident.bits());
+            )+
+        }
+
+        impl SpecifiedValueInfo for FontVariantLigatures {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["normal", $($css,)+]);
+            }
+        }
+    }
+}
+
+impl_variant_ligatures! {
+    /// Specifies that all types of ligatures and contextual forms
+    /// covered by this property are explicitly disabled
+    NONE / "none" => NS_FONT_VARIANT_LIGATURES_NONE = 0x01,
+    /// Enables display of common ligatures
+    COMMON_LIGATURES / "common-ligatures" => NS_FONT_VARIANT_LIGATURES_COMMON = 0x02,
+    /// Disables display of common ligatures
+    NO_COMMON_LIGATURES / "no-common-ligatures" => NS_FONT_VARIANT_LIGATURES_NO_COMMON = 0x04,
+    /// Enables display of discretionary ligatures
+    DISCRETIONARY_LIGATURES / "discretionary-ligatures" => NS_FONT_VARIANT_LIGATURES_DISCRETIONARY = 0x08,
+    /// Disables display of discretionary ligatures
+    NO_DISCRETIONARY_LIGATURES / "no-discretionary-ligatures" => NS_FONT_VARIANT_LIGATURES_NO_DISCRETIONARY = 0x10,
+    /// Enables display of historical ligatures
+    HISTORICAL_LIGATURES / "historical-ligatures" => NS_FONT_VARIANT_LIGATURES_HISTORICAL = 0x20,
+    /// Disables display of historical ligatures
+    NO_HISTORICAL_LIGATURES / "no-historical-ligatures" => NS_FONT_VARIANT_LIGATURES_NO_HISTORICAL = 0x40,
+    /// Enables display of contextual alternates
+    CONTEXTUAL / "contextual" => NS_FONT_VARIANT_LIGATURES_CONTEXTUAL = 0x80,
+    /// Disables display of contextual alternates
+    NO_CONTEXTUAL / "no-contextual" => NS_FONT_VARIANT_LIGATURES_NO_CONTEXTUAL = 0x100,
+}
+
+#[cfg(feature = "gecko")]
+impl FontVariantLigatures {
+    /// Obtain a specified value from a Gecko keyword value
+    ///
+    /// Intended for use with presentation attributes, not style structs
+    pub fn from_gecko_keyword(kw: u16) -> Self {
+        Self::from_bits_truncate(kw)
+    }
+
+    /// Transform into gecko keyword
+    pub fn to_gecko_keyword(self) -> u16 {
+        self.bits()
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl_gecko_keyword_conversions!(FontVariantLigatures, u16);
+
+impl Parse for FontVariantLigatures {
+    /// normal | none |
+    /// [ <common-lig-values> ||
+    ///   <discretionary-lig-values> ||
+    ///   <historical-lig-values> ||
+    ///   <contextual-alt-values> ]
+    /// <common-lig-values>        = [ common-ligatures | no-common-ligatures ]
+    /// <discretionary-lig-values> = [ discretionary-ligatures | no-discretionary-ligatures ]
+    /// <historical-lig-values>    = [ historical-ligatures | no-historical-ligatures ]
+    /// <contextual-alt-values>    = [ contextual | no-contextual ]
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let mut result = Self::empty();
+        if input
+            .try_parse(|input| input.expect_ident_matching("normal"))
+            .is_ok()
+        {
+            return Ok(result);
+        }
+        if input
+            .try_parse(|input| input.expect_ident_matching("none"))
+            .is_ok()
+        {
+            return Ok(Self::NONE);
+        }
+
+        while let Ok(flag) = input.try_parse(|input| {
+            Ok(
+                match_ignore_ascii_case! { &input.expect_ident().map_err(|_| ())?,
+                    "common-ligatures" =>
+                        exclusive_value!((result, Self::COMMON_LIGATURES |
+                                                  Self::NO_COMMON_LIGATURES
+                                        ) => Self::COMMON_LIGATURES),
+                    "no-common-ligatures" =>
+                        exclusive_value!((result, Self::COMMON_LIGATURES |
+                                                  Self::NO_COMMON_LIGATURES
+                                        ) => Self::NO_COMMON_LIGATURES),
+                    "discretionary-ligatures" =>
+                        exclusive_value!((result, Self::DISCRETIONARY_LIGATURES |
+                                                  Self::NO_DISCRETIONARY_LIGATURES
+                                        ) => Self::DISCRETIONARY_LIGATURES),
+                    "no-discretionary-ligatures" =>
+                        exclusive_value!((result, Self::DISCRETIONARY_LIGATURES |
+                                                  Self::NO_DISCRETIONARY_LIGATURES
+                                        ) => Self::NO_DISCRETIONARY_LIGATURES),
+                    "historical-ligatures" =>
+                        exclusive_value!((result, Self::HISTORICAL_LIGATURES |
+                                                  Self::NO_HISTORICAL_LIGATURES
+                                        ) => Self::HISTORICAL_LIGATURES),
+                    "no-historical-ligatures" =>
+                        exclusive_value!((result, Self::HISTORICAL_LIGATURES |
+                                                  Self::NO_HISTORICAL_LIGATURES
+                                        ) => Self::NO_HISTORICAL_LIGATURES),
+                    "contextual" =>
+                        exclusive_value!((result, Self::CONTEXTUAL |
+                                                  Self::NO_CONTEXTUAL
+                                        ) => Self::CONTEXTUAL),
+                    "no-contextual" =>
+                        exclusive_value!((result, Self::CONTEXTUAL |
+                                                  Self::NO_CONTEXTUAL
+                                        ) => Self::NO_CONTEXTUAL),
+                    _ => return Err(()),
+                },
+            )
+        }) {
+            result.insert(flag);
+        }
+
+        if !result.is_empty() {
+            Ok(result)
+        } else {
+            Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+        }
+    }
+}
+
+macro_rules! impl_variant_numeric {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $gecko:ident = $value:expr,
+        )+
+    } => {
+        #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToResolvedValue, ToShmem)]
+        /// Variants of numeric values
+        pub struct FontVariantNumeric(u8);
+        bitflags! {
+            impl FontVariantNumeric: u8 {
+                /// None of other variants are enabled.
+                const NORMAL = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+            }
+        }
+
+        impl ToCss for FontVariantNumeric {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("normal");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.intersects(FontVariantNumeric::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
+        #[cfg(feature = "gecko")]
+        #[inline]
+        pub fn assert_variant_numeric_matches() {
+            use crate::gecko_bindings::structs;
+            $(
+                debug_assert_eq!(structs::$gecko as u8, FontVariantNumeric::$ident.bits());
+            )+
+        }
+
+        impl SpecifiedValueInfo for FontVariantNumeric {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["normal", $($css,)+]);
+            }
+        }
+    }
+}
+
+impl_variant_numeric! {
+    /// Enables display of lining numerals.
+    LINING_NUMS / "lining-nums" => NS_FONT_VARIANT_NUMERIC_LINING = 0x01,
+    /// Enables display of old-style numerals.
+    OLDSTYLE_NUMS / "oldstyle-nums" => NS_FONT_VARIANT_NUMERIC_OLDSTYLE = 0x02,
+    /// Enables display of proportional numerals.
+    PROPORTIONAL_NUMS / "proportional-nums" => NS_FONT_VARIANT_NUMERIC_PROPORTIONAL = 0x04,
+    /// Enables display of tabular numerals.
+    TABULAR_NUMS / "tabular-nums" => NS_FONT_VARIANT_NUMERIC_TABULAR = 0x08,
+    /// Enables display of lining diagonal fractions.
+    DIAGONAL_FRACTIONS / "diagonal-fractions" => NS_FONT_VARIANT_NUMERIC_DIAGONAL_FRACTIONS = 0x10,
+    /// Enables display of lining stacked fractions.
+    STACKED_FRACTIONS / "stacked-fractions" => NS_FONT_VARIANT_NUMERIC_STACKED_FRACTIONS = 0x20,
+    /// Enables display of letter forms used with ordinal numbers.
+    ORDINAL / "ordinal" => NS_FONT_VARIANT_NUMERIC_ORDINAL = 0x80,
+    /// Enables display of slashed zeros.
+    SLASHED_ZERO / "slashed-zero" => NS_FONT_VARIANT_NUMERIC_SLASHZERO = 0x40,
+}
+
+#[cfg(feature = "gecko")]
+impl FontVariantNumeric {
+    /// Obtain a specified value from a Gecko keyword value
+    ///
+    /// Intended for use with presentation attributes, not style structs
+    pub fn from_gecko_keyword(kw: u8) -> Self {
+        Self::from_bits_truncate(kw)
+    }
+
+    /// Transform into gecko keyword
+    pub fn to_gecko_keyword(self) -> u8 {
+        self.bits()
+    }
+}
+
+#[cfg(feature = "gecko")]
+impl_gecko_keyword_conversions!(FontVariantNumeric, u8);
+
+impl Parse for FontVariantNumeric {
+    /// normal |
+    ///  [ <numeric-figure-values>   ||
+    ///    <numeric-spacing-values>  ||
+    ///    <numeric-fraction-values> ||
+    ///    ordinal                   ||
+    ///    slashed-zero ]
+    /// <numeric-figure-values>   = [ lining-nums | oldstyle-nums ]
+    /// <numeric-spacing-values>  = [ proportional-nums | tabular-nums ]
+    /// <numeric-fraction-values> = [ diagonal-fractions | stacked-fractions ]
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let mut result = Self::empty();
+
+        if input
+            .try_parse(|input| input.expect_ident_matching("normal"))
+            .is_ok()
+        {
+            return Ok(result);
+        }
+
+        while let Ok(flag) = input.try_parse(|input| {
+            Ok(
+                match_ignore_ascii_case! { &input.expect_ident().map_err(|_| ())?,
+                    "ordinal" =>
+                        exclusive_value!((result, Self::ORDINAL) => Self::ORDINAL),
+                    "slashed-zero" =>
+                        exclusive_value!((result, Self::SLASHED_ZERO) => Self::SLASHED_ZERO),
+                    "lining-nums" =>
+                        exclusive_value!((result, Self::LINING_NUMS |
+                                                  Self::OLDSTYLE_NUMS
+                                        ) => Self::LINING_NUMS),
+                    "oldstyle-nums" =>
+                        exclusive_value!((result, Self::LINING_NUMS |
+                                                  Self::OLDSTYLE_NUMS
+                                        ) => Self::OLDSTYLE_NUMS),
+                    "proportional-nums" =>
+                        exclusive_value!((result, Self::PROPORTIONAL_NUMS |
+                                                  Self::TABULAR_NUMS
+                                        ) => Self::PROPORTIONAL_NUMS),
+                    "tabular-nums" =>
+                        exclusive_value!((result, Self::PROPORTIONAL_NUMS |
+                                                  Self::TABULAR_NUMS
+                                        ) => Self::TABULAR_NUMS),
+                    "diagonal-fractions" =>
+                        exclusive_value!((result, Self::DIAGONAL_FRACTIONS |
+                                                  Self::STACKED_FRACTIONS
+                                        ) => Self::DIAGONAL_FRACTIONS),
+                    "stacked-fractions" =>
+                        exclusive_value!((result, Self::DIAGONAL_FRACTIONS |
+                                                  Self::STACKED_FRACTIONS
+                                        ) => Self::STACKED_FRACTIONS),
+                    _ => return Err(()),
+                },
+            )
+        }) {
+            result.insert(flag);
+        }
+
+        if !result.is_empty() {
+            Ok(result)
+        } else {
+            Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+        }
+    }
+}
+
+/// This property provides low-level control over OpenType or TrueType font features.
+pub type FontFeatureSettings = FontSettings<FeatureTagValue<Integer>>;
+
+/// For font-language-override, use the same representation as the computed value.
+pub use crate::values::computed::font::FontLanguageOverride;
+
+impl Parse for FontLanguageOverride {
+    /// normal | <string>
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<FontLanguageOverride, ParseError<'i>> {
+        if input
+            .try_parse(|input| input.expect_ident_matching("normal"))
+            .is_ok()
+        {
+            return Ok(FontLanguageOverride::normal());
+        }
+
+        let string = input.expect_string()?;
+
+        // The OpenType spec requires tags to be 1 to 4 ASCII characters:
+        // https://learn.microsoft.com/en-gb/typography/opentype/spec/otff#data-types
+        if string.is_empty() || string.len() > 4 || !string.is_ascii() {
+            return Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError));
+        }
+
+        let mut bytes = [b' '; 4];
+        for (byte, str_byte) in bytes.iter_mut().zip(string.as_bytes()) {
+            *byte = *str_byte;
+        }
+
+        Ok(FontLanguageOverride(u32::from_be_bytes(bytes)))
+    }
+}
+
+/// A value for any of the font-synthesis-{weight,style,small-caps} properties.
+#[repr(u8)]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+pub enum FontSynthesis {
+    /// This attribute may be synthesized if not supported by a face.
+    Auto,
+    /// Do not attempt to synthesis this style attribute.
+    None,
+}
+
+#[derive(
+    Clone,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(C)]
+/// Allows authors to choose a palette from those supported by a color font
+/// (and potentially @font-palette-values overrides).
+pub struct FontPalette(Atom);
+
+#[allow(missing_docs)]
+impl FontPalette {
+    pub fn normal() -> Self {
+        Self(atom!("normal"))
+    }
+    pub fn light() -> Self {
+        Self(atom!("light"))
+    }
+    pub fn dark() -> Self {
+        Self(atom!("dark"))
+    }
+}
+
+impl Parse for FontPalette {
+    /// normal | light | dark | dashed-ident
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<FontPalette, ParseError<'i>> {
+        let location = input.current_source_location();
+        let ident = input.expect_ident()?;
+        match_ignore_ascii_case! { &ident,
+            "normal" => Ok(Self::normal()),
+            "light" => Ok(Self::light()),
+            "dark" => Ok(Self::dark()),
+            _ => if ident.starts_with("--") {
+                Ok(Self(Atom::from(ident.as_ref())))
+            } else {
+                Err(location.new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone())))
+            },
+        }
+    }
+}
+
+impl ToCss for FontPalette {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        serialize_atom_identifier(&self.0, dest)
+    }
+}
+
+/// This property provides low-level control over OpenType or TrueType font
+/// variations.
+pub type FontVariationSettings = FontSettings<VariationValue<Number>>;
+
+fn parse_one_feature_value<'i, 't>(
+    context: &ParserContext,
+    input: &mut Parser<'i, 't>,
+) -> Result<Integer, ParseError<'i>> {
+    if let Ok(integer) = input.try_parse(|i| Integer::parse_non_negative(context, i)) {
+        return Ok(integer);
+    }
+
+    try_match_ident_ignore_ascii_case! { input,
+        "on" => Ok(Integer::new(1)),
+        "off" => Ok(Integer::new(0)),
+    }
+}
+
+impl Parse for FeatureTagValue<Integer> {
+    /// https://drafts.csswg.org/css-fonts-4/#feature-tag-value
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let tag = FontTag::parse(context, input)?;
+        let value = input
+            .try_parse(|i| parse_one_feature_value(context, i))
+            .unwrap_or_else(|_| Integer::new(1));
+
+        Ok(Self { tag, value })
+    }
+}
+
+impl Parse for VariationValue<Number> {
+    /// This is the `<string> <number>` part of the font-variation-settings
+    /// syntax.
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let tag = FontTag::parse(context, input)?;
+        let value = Number::parse(context, input)?;
+        Ok(Self { tag, value })
+    }
+}
+
+/// A metrics override value for a @font-face descriptor
+///
+/// https://drafts.csswg.org/css-fonts/#font-metrics-override-desc
+#[derive(
+    Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo, ToCss, ToShmem,
+)]
+pub enum MetricsOverride {
+    /// A non-negative `<percentage>` of the computed font size
+    Override(NonNegativePercentage),
+    /// Normal metrics from the font.
+    Normal,
+}
+
+impl MetricsOverride {
+    #[inline]
+    /// Get default value with `normal`
+    pub fn normal() -> MetricsOverride {
+        MetricsOverride::Normal
+    }
+
+    /// The ToComputedValue implementation, used for @font-face descriptors.
+    ///
+    /// Valid override percentages must be non-negative; we return -1.0 to indicate
+    /// the absence of an override (i.e. 'normal').
+    #[inline]
+    pub fn compute(&self) -> ComputedPercentage {
+        match *self {
+            MetricsOverride::Normal => ComputedPercentage(-1.0),
+            MetricsOverride::Override(percent) => ComputedPercentage(percent.0.get()),
+        }
+    }
+}
+
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(u8)]
+/// How to do font-size scaling.
+pub enum XTextScale {
+    /// Both min-font-size and text zoom are enabled.
+    All,
+    /// Text-only zoom is enabled, but min-font-size is not honored.
+    ZoomOnly,
+    /// Neither of them is enabled.
+    None,
+}
+
+impl XTextScale {
+    /// Returns whether text zoom is enabled.
+    #[inline]
+    pub fn text_zoom_enabled(self) -> bool {
+        self != Self::None
+    }
+}
+
+#[derive(
+    Clone,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+/// Internal property that reflects the lang attribute
+pub struct XLang(#[css(skip)] pub Atom);
+
+impl XLang {
+    #[inline]
+    /// Get default value for `-x-lang`
+    pub fn get_initial_value() -> XLang {
+        XLang(atom!(""))
+    }
+}
+
+impl Parse for XLang {
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<XLang, ParseError<'i>> {
+        debug_assert!(
+            false,
+            "Should be set directly by presentation attributes only."
+        );
+        Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+    }
+}
+
+#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+/// Specifies the minimum font size allowed due to changes in scriptlevel.
+/// Ref: https://wiki.mozilla.org/MathML:mstyle
+pub struct MozScriptMinSize(pub NoCalcLength);
+
+impl MozScriptMinSize {
+    #[inline]
+    /// Calculate initial value of -moz-script-min-size.
+    pub fn get_initial_value() -> Length {
+        Length::new(DEFAULT_SCRIPT_MIN_SIZE_PT as f32 * PX_PER_PT)
+    }
+}
+
+impl Parse for MozScriptMinSize {
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<MozScriptMinSize, ParseError<'i>> {
+        debug_assert!(
+            false,
+            "Should be set directly by presentation attributes only."
+        );
+        Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+    }
+}
+
+/// A value for the `math-depth` property.
+/// https://mathml-refresh.github.io/mathml-core/#the-math-script-level-property
+#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToCss, ToShmem)]
+pub enum MathDepth {
+    /// Increment math-depth if math-style is compact.
+    AutoAdd,
+
+    /// Add the function's argument to math-depth.
+    #[css(function)]
+    Add(Integer),
+
+    /// Set math-depth to the specified value.
+    Absolute(Integer),
+}
+
+impl Parse for MathDepth {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<MathDepth, ParseError<'i>> {
+        if input
+            .try_parse(|i| i.expect_ident_matching("auto-add"))
+            .is_ok()
+        {
+            return Ok(MathDepth::AutoAdd);
+        }
+        if let Ok(math_depth_value) = input.try_parse(|input| Integer::parse(context, input)) {
+            return Ok(MathDepth::Absolute(math_depth_value));
+        }
+        input.expect_function_matching("add")?;
+        let math_depth_delta_value =
+            input.parse_nested_block(|input| Integer::parse(context, input))?;
+        Ok(MathDepth::Add(math_depth_delta_value))
+    }
+}
+
+#[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+/// Specifies the multiplier to be used to adjust font size
+/// due to changes in scriptlevel.
+///
+/// Ref: https://www.w3.org/TR/MathML3/chapter3.html#presm.mstyle.attrs
+pub struct MozScriptSizeMultiplier(pub f32);
+
+impl MozScriptSizeMultiplier {
+    #[inline]
+    /// Get default value of `-moz-script-size-multiplier`
+    pub fn get_initial_value() -> MozScriptSizeMultiplier {
+        MozScriptSizeMultiplier(DEFAULT_SCRIPT_SIZE_MULTIPLIER as f32)
+    }
+}
+
+impl Parse for MozScriptSizeMultiplier {
+    fn parse<'i, 't>(
+        _: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<MozScriptSizeMultiplier, ParseError<'i>> {
+        debug_assert!(
+            false,
+            "Should be set directly by presentation attributes only."
+        );
+        Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+    }
+}
+
+impl From<f32> for MozScriptSizeMultiplier {
+    fn from(v: f32) -> Self {
+        MozScriptSizeMultiplier(v)
+    }
+}
+
+impl From<MozScriptSizeMultiplier> for f32 {
+    fn from(v: MozScriptSizeMultiplier) -> f32 {
+        v.0
+    }
+}
+
+/// A specified value for the `line-height` property.
+pub type LineHeight = GenericLineHeight<NonNegativeNumber, NonNegativeLengthPercentage>;
+
+impl ToComputedValue for LineHeight {
+    type ComputedValue = computed::LineHeight;
+
+    #[inline]
+    fn to_computed_value(&self, context: &Context) -> Self::ComputedValue {
+        match *self {
+            GenericLineHeight::Normal => GenericLineHeight::Normal,
+            #[cfg(feature = "gecko")]
+            GenericLineHeight::MozBlockHeight => GenericLineHeight::MozBlockHeight,
+            GenericLineHeight::Number(number) => {
+                GenericLineHeight::Number(number.to_computed_value(context))
+            },
+            GenericLineHeight::Length(ref non_negative_lp) => {
+                let result = match non_negative_lp.0 {
+                    LengthPercentage::Length(NoCalcLength::Absolute(ref abs)) => {
+                        context.maybe_zoom_text(abs.to_computed_value(context))
+                    },
+                    LengthPercentage::Length(ref length) => {
+                        // line-height units specifically resolve against parent's
+                        // font and line-height properties, while the rest of font
+                        // relative units still resolve against the element's own
+                        // properties.
+                        length.to_computed_value_with_base_size(
+                            context,
+                            FontBaseSize::CurrentStyle,
+                            LineHeightBase::InheritedStyle,
+                        )
+                    },
+                    LengthPercentage::Percentage(ref p) => FontRelativeLength::Em(p.0)
+                        .to_computed_value(
+                            context,
+                            FontBaseSize::CurrentStyle,
+                            LineHeightBase::InheritedStyle,
+                        ),
+                    LengthPercentage::Calc(ref calc) => {
+                        let computed_calc = calc.to_computed_value_zoomed(
+                            context,
+                            FontBaseSize::CurrentStyle,
+                            LineHeightBase::InheritedStyle,
+                        );
+                        let base = context.style().get_font().clone_font_size().computed_size();
+                        computed_calc.resolve(base)
+                    },
+                };
+                GenericLineHeight::Length(result.into())
+            },
+        }
+    }
+
+    #[inline]
+    fn from_computed_value(computed: &Self::ComputedValue) -> Self {
+        match *computed {
+            GenericLineHeight::Normal => GenericLineHeight::Normal,
+            #[cfg(feature = "gecko")]
+            GenericLineHeight::MozBlockHeight => GenericLineHeight::MozBlockHeight,
+            GenericLineHeight::Number(ref number) => {
+                GenericLineHeight::Number(NonNegativeNumber::from_computed_value(number))
+            },
+            GenericLineHeight::Length(ref length) => {
+                GenericLineHeight::Length(NoCalcLength::from_computed_value(&length.0).into())
+            },
+        }
+    }
+}