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diff --git a/servo/components/style/values/generics/easing.rs b/servo/components/style/values/generics/easing.rs
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+++ b/servo/components/style/values/generics/easing.rs
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+/* 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/. */
+
+//! Generic types for CSS Easing Functions.
+//! https://drafts.csswg.org/css-easing/#timing-functions
+
+use crate::parser::ParserContext;
+
+/// A generic easing function.
+#[derive(
+    Clone,
+    Debug,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToCss,
+    ToShmem,
+    Serialize,
+    Deserialize,
+)]
+#[value_info(ty = "TIMING_FUNCTION")]
+#[repr(u8, C)]
+/// cbindgen:private-default-tagged-enum-constructor=false
+pub enum TimingFunction<Integer, Number, LinearStops> {
+    /// `linear | ease | ease-in | ease-out | ease-in-out`
+    Keyword(TimingKeyword),
+    /// `cubic-bezier(<number>, <number>, <number>, <number>)`
+    #[allow(missing_docs)]
+    #[css(comma, function)]
+    CubicBezier {
+        x1: Number,
+        y1: Number,
+        x2: Number,
+        y2: Number,
+    },
+    /// `step-start | step-end | steps(<integer>, [ <step-position> ]?)`
+    /// `<step-position> = jump-start | jump-end | jump-none | jump-both | start | end`
+    #[css(comma, function)]
+    #[value_info(other_values = "step-start,step-end")]
+    Steps(Integer, #[css(skip_if = "is_end")] StepPosition),
+    /// linear([<linear-stop>]#)
+    /// <linear-stop> = <output> && <linear-stop-length>?
+    /// <linear-stop-length> = <percentage>{1, 2}
+    #[css(function = "linear")]
+    LinearFunction(LinearStops),
+}
+
+#[allow(missing_docs)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+    Serialize,
+    Deserialize,
+)]
+#[repr(u8)]
+pub enum TimingKeyword {
+    Linear,
+    Ease,
+    EaseIn,
+    EaseOut,
+    EaseInOut,
+}
+
+/// Before flag, defined as per https://drafts.csswg.org/css-easing/#before-flag
+/// This flag is never user-specified.
+#[allow(missing_docs)]
+#[derive(PartialEq)]
+#[repr(u8)]
+pub enum BeforeFlag {
+    Unset,
+    Set,
+}
+
+#[cfg(feature = "gecko")]
+fn step_position_jump_enabled(_context: &ParserContext) -> bool {
+    static_prefs::pref!("layout.css.step-position-jump.enabled")
+}
+
+#[cfg(feature = "servo")]
+fn step_position_jump_enabled(_context: &ParserContext) -> bool {
+    false
+}
+
+#[allow(missing_docs)]
+#[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(
+    Clone,
+    Copy,
+    Debug,
+    Eq,
+    MallocSizeOf,
+    Parse,
+    PartialEq,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+    Serialize,
+    Deserialize,
+)]
+#[repr(u8)]
+pub enum StepPosition {
+    #[parse(condition = "step_position_jump_enabled")]
+    JumpStart,
+    #[parse(condition = "step_position_jump_enabled")]
+    JumpEnd,
+    #[parse(condition = "step_position_jump_enabled")]
+    JumpNone,
+    #[parse(condition = "step_position_jump_enabled")]
+    JumpBoth,
+    Start,
+    End,
+}
+
+#[inline]
+fn is_end(position: &StepPosition) -> bool {
+    *position == StepPosition::JumpEnd || *position == StepPosition::End
+}
+
+impl<Integer, Number, LinearStops> TimingFunction<Integer, Number, LinearStops> {
+    /// `ease`
+    #[inline]
+    pub fn ease() -> Self {
+        TimingFunction::Keyword(TimingKeyword::Ease)
+    }
+}