diff --git a/components/style/gecko/url.rs b/components/style/gecko/url.rs
index 1b5bc424e4d..a0ecfc7b381 100644
--- a/components/style/gecko/url.rs
+++ b/components/style/gecko/url.rs
@@ -15,7 +15,7 @@ use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use parser::{Parse, ParserContext};
 use servo_arc::{Arc, RawOffsetArc};
 use std::mem;
-use style_traits::ParseError;
+use style_traits::{ParseError, SpecifiedValueInfo};
 
 /// A CSS url() value for gecko.
 #[css(function = "url")]
@@ -120,8 +120,10 @@ impl MallocSizeOf for CssUrl {
     }
 }
 
+impl SpecifiedValueInfo for CssUrl {}
+
 /// A specified url() value for general usage.
-#[derive(Clone, Debug, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub struct SpecifiedUrl {
     /// The specified url value.
     pub url: CssUrl,
@@ -179,7 +181,7 @@ impl MallocSizeOf for SpecifiedUrl {
 /// A specified url() value for image.
 ///
 /// This exists so that we can construct `ImageValue` and reuse it.
-#[derive(Clone, Debug, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub struct SpecifiedImageUrl {
     /// The specified url value.
     pub url: CssUrl,
diff --git a/components/style/gecko_string_cache/mod.rs b/components/style/gecko_string_cache/mod.rs
index ead705fa231..297599e2080 100644
--- a/components/style/gecko_string_cache/mod.rs
+++ b/components/style/gecko_string_cache/mod.rs
@@ -20,6 +20,7 @@ use std::fmt::{self, Write};
 use std::hash::{Hash, Hasher};
 use std::iter::Cloned;
 use std::ops::Deref;
+use style_traits::SpecifiedValueInfo;
 
 #[macro_use]
 #[allow(improper_ctypes, non_camel_case_types, missing_docs)]
@@ -415,3 +416,5 @@ impl From<String> for Atom {
 }
 
 malloc_size_of_is_0!(Atom);
+
+impl SpecifiedValueInfo for Atom {}
diff --git a/components/style/macros.rs b/components/style/macros.rs
index f8f4759c148..671ba35b8bc 100644
--- a/components/style/macros.rs
+++ b/components/style/macros.rs
@@ -68,8 +68,9 @@ macro_rules! try_match_ident_ignore_ascii_case {
 macro_rules! define_keyword_type {
     ($name:ident, $css:expr) => {
         #[allow(missing_docs)]
-        #[derive(Animate, Clone, ComputeSquaredDistance, Copy, MallocSizeOf, PartialEq,
-                 ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
+        #[derive(Animate, Clone, ComputeSquaredDistance, Copy, MallocSizeOf,
+                 PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+                 ToComputedValue, ToCss)]
         pub struct $name;
 
         impl fmt::Debug for $name {
diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index 90e070d03c4..3c5bb762e1f 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -164,7 +164,7 @@
         % if separator == "Comma":
         #[css(comma)]
         % endif
-        #[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+        #[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
         pub struct SpecifiedValue(
             % if not allow_empty:
             #[css(iterable)]
@@ -396,8 +396,8 @@
 
         pub mod computed_value {
             #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-            #[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse)]
-            #[derive(PartialEq, ToCss)]
+            #[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse,
+                     PartialEq, SpecifiedValueInfo, ToCss)]
             pub enum T {
             % for value in keyword.values_for(product):
                 ${to_camel_case(value)},
@@ -408,7 +408,7 @@
         }
 
         #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-        #[derive(Clone, Copy, Debug, Eq, PartialEq, ToCss)]
+        #[derive(Clone, Copy, Debug, Eq, PartialEq, SpecifiedValueInfo, ToCss)]
         pub enum SpecifiedValue {
             Keyword(computed_value::T),
             System(SystemFont),
@@ -558,7 +558,8 @@
         </%def>
         % if extra_specified:
             #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-            #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToCss)]
+            #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+                     SpecifiedValueInfo, ToCss)]
             pub enum SpecifiedValue {
                 ${variants(keyword.values_for(product) + extra_specified.split(), bool(extra_specified))}
             }
@@ -569,7 +570,7 @@
             #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
             #[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
             % if not extra_specified:
-            #[derive(Parse, ToComputedValue)]
+            #[derive(Parse, SpecifiedValueInfo, ToComputedValue)]
             % endif
             pub enum T {
                 ${variants(data.longhands_by_name[name].keyword.values_for(product), not extra_specified)}
@@ -634,7 +635,7 @@
         #[allow(unused_imports)]
         use style_traits::{ParseError, StyleParseErrorKind};
         #[allow(unused_imports)]
-        use style_traits::{CssWriter, ToCss};
+        use style_traits::{CssWriter, SpecifiedValueInfo, ToCss};
 
         pub struct Longhands {
             % for sub_property in shorthand.sub_properties:
@@ -742,6 +743,26 @@
             })
         }
 
+        <%
+            sub_properties_for_value_info = shorthand.sub_properties
+            if shorthand.name == "border":
+                # border-image subproperties are simply reset by border
+                # shorthand, so border cannot accept values of them.
+                # XXX We may want a better mechanism for this, but this
+                # is probably fine for now.
+                sub_properties_for_value_info = [
+                    subprop for subprop in shorthand.sub_properties
+                    if not subprop.name.startswith("border-image")
+                ]
+        %>
+        impl SpecifiedValueInfo for Longhands {
+            const SUPPORTED_TYPES: u8 = 0
+                % for subprop in sub_properties_for_value_info:
+                | <longhands::${subprop.ident}::SpecifiedValue as SpecifiedValueInfo>::SUPPORTED_TYPES
+                % endfor
+                ;
+        }
+
         ${caller.body()}
     }
     % endif
diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index e2d15139128..059d5a51c1b 100644
--- a/components/style/properties/helpers/animated_properties.mako.rs
+++ b/components/style/properties/helpers/animated_properties.mako.rs
@@ -27,7 +27,7 @@ use smallvec::SmallVec;
 use std::{cmp, ptr};
 use std::mem::{self, ManuallyDrop};
 #[cfg(feature = "gecko")] use hash::FnvHashMap;
-use style_traits::ParseError;
+use style_traits::{ParseError, SpecifiedValueInfo};
 use super::ComputedValues;
 use values::{CSSFloat, CustomIdent, Either};
 use values::animated::{Animate, Procedure, ToAnimatedValue, ToAnimatedZero};
@@ -172,6 +172,8 @@ impl From<nsCSSPropertyID> for TransitionProperty {
     }
 }
 
+impl SpecifiedValueInfo for TransitionProperty {}
+
 /// Returns true if this nsCSSPropertyID is one of the transitionable properties.
 #[cfg(feature = "gecko")]
 pub fn nscsspropertyid_is_transitionable(property: nsCSSPropertyID) -> bool {
diff --git a/components/style/properties/longhand/font.mako.rs b/components/style/properties/longhand/font.mako.rs
index 0477a2cd0d5..3cd10daf96b 100644
--- a/components/style/properties/longhand/font.mako.rs
+++ b/components/style/properties/longhand/font.mako.rs
@@ -296,7 +296,8 @@ ${helpers.predefined_type("-x-text-zoom",
             kw_cast = """font_variant_caps font_kerning font_variant_position
                          font_optical_sizing""".split()
         %>
-        #[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, PartialEq, ToCss)]
+        #[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, PartialEq,
+                 SpecifiedValueInfo, ToCss)]
         pub enum SystemFont {
             % for font in system_fonts:
                 ${to_camel_case(font)},
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 1f9c3b49513..da1bbb9f149 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -42,7 +42,8 @@ use selector_parser::PseudoElement;
 use selectors::parser::SelectorParseErrorKind;
 #[cfg(feature = "servo")] use servo_config::prefs::PREFS;
 use shared_lock::StylesheetGuards;
-use style_traits::{CssWriter, ParseError, ParsingMode, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, ParseError, ParsingMode};
+use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 use stylesheets::{CssRuleType, Origin, UrlExtraData};
 #[cfg(feature = "servo")] use values::Either;
 use values::generics::text::LineHeight;
@@ -541,6 +542,24 @@ impl NonCustomPropertyId {
 
         false
     }
+
+    /// The supported types of this property. The return value should be
+    /// style_traits::CssType when it can become a bitflags type.
+    fn supported_types(&self) -> u8 {
+        const SUPPORTED_TYPES: [u8; ${len(data.longhands) + len(data.shorthands)}] = [
+            % for prop in data.longhands:
+                <${prop.specified_type()} as SpecifiedValueInfo>::SUPPORTED_TYPES,
+            % endfor
+            % for prop in data.shorthands:
+            % if prop.name == "all":
+                0, // 'all' accepts no value other than CSS-wide keywords
+            % else:
+                <shorthands::${prop.ident}::Longhands as SpecifiedValueInfo>::SUPPORTED_TYPES,
+            % endif
+            % endfor
+        ];
+        SUPPORTED_TYPES[self.0]
+    }
 }
 
 impl From<LonghandId> for NonCustomPropertyId {
@@ -1713,6 +1732,19 @@ impl PropertyId {
         };
         id.allowed_in(context)
     }
+
+    /// Whether the property supports the given CSS type.
+    /// `ty` should a bitflags of constants in style_traits::CssType.
+    pub fn supports_type(&self, ty: u8) -> bool {
+        let non_custom_id: NonCustomPropertyId = match *self {
+            PropertyId::Custom(_) => return false,
+            PropertyId::Shorthand(id) => id.into(),
+            PropertyId::Longhand(id) => id.into(),
+            PropertyId::ShorthandAlias(id, _) => id.into(),
+            PropertyId::LonghandAlias(id, _) => id.into(),
+        };
+        non_custom_id.supported_types() & ty != 0
+    }
 }
 
 /// A declaration using a CSS-wide keyword.
diff --git a/components/style/values/computed/length.rs b/components/style/values/computed/length.rs
index fd63ec7e666..beb33553d7f 100644
--- a/components/style/values/computed/length.rs
+++ b/components/style/values/computed/length.rs
@@ -916,7 +916,8 @@ pub type NonNegativeLengthOrPercentageOrNormal = Either<NonNegativeLengthOrPerce
 /// block-size, and inline-size.
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToCss)]
 pub enum ExtremumLength {
     MozMaxContent,
     MozMinContent,
diff --git a/components/style/values/generics/background.rs b/components/style/values/generics/background.rs
index 91c6f4ef06c..ad42fcfb555 100644
--- a/components/style/values/generics/background.rs
+++ b/components/style/values/generics/background.rs
@@ -5,8 +5,8 @@
 //! Generic types for CSS values related to backgrounds.
 
 /// A generic value for the `background-size` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum BackgroundSize<LengthOrPercentageOrAuto> {
     /// `<width> <height>`
     Explicit {
diff --git a/components/style/values/generics/basic_shape.rs b/components/style/values/generics/basic_shape.rs
index 0da3b53f2c8..80375ad8ffa 100644
--- a/components/style/values/generics/basic_shape.rs
+++ b/components/style/values/generics/basic_shape.rs
@@ -18,7 +18,8 @@ pub type ClippingShape<BasicShape, Url> = ShapeSource<BasicShape, GeometryBox, U
 
 /// <https://drafts.fxtf.org/css-masking-1/#typedef-geometry-box>
 #[allow(missing_docs)]
-#[derive(Animate, Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, Copy, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum GeometryBox {
     FillBox,
     StrokeBox,
@@ -32,7 +33,8 @@ pub type FloatAreaShape<BasicShape, Image> = ShapeSource<BasicShape, ShapeBox, I
 /// https://drafts.csswg.org/css-shapes-1/#typedef-shape-box
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Animate, Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum ShapeBox {
     MarginBox,
     BorderBox,
@@ -43,7 +45,8 @@ pub enum ShapeBox {
 /// A shape source, for some reference box.
 #[allow(missing_docs)]
 #[animation(no_bound(ImageOrUrl))]
-#[derive(Animate, Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum ShapeSource<BasicShape, ReferenceBox, ImageOrUrl> {
     #[animation(error)]
     ImageOrUrl(ImageOrUrl),
@@ -55,8 +58,8 @@ pub enum ShapeSource<BasicShape, ReferenceBox, ImageOrUrl> {
 }
 
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToComputedValue,
-         ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum BasicShape<H, V, LengthOrPercentage> {
     Inset(#[css(field_bound)] InsetRect<LengthOrPercentage>),
     Circle(#[css(field_bound)] Circle<H, V, LengthOrPercentage>),
@@ -66,7 +69,8 @@ pub enum BasicShape<H, V, LengthOrPercentage> {
 
 /// <https://drafts.csswg.org/css-shapes/#funcdef-inset>
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToComputedValue)]
 pub struct InsetRect<LengthOrPercentage> {
     pub rect: Rect<LengthOrPercentage>,
     pub round: Option<BorderRadius<LengthOrPercentage>>,
@@ -74,8 +78,8 @@ pub struct InsetRect<LengthOrPercentage> {
 
 /// <https://drafts.csswg.org/css-shapes/#funcdef-circle>
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue)]
 pub struct Circle<H, V, LengthOrPercentage> {
     pub position: Position<H, V>,
     pub radius: ShapeRadius<LengthOrPercentage>,
@@ -83,8 +87,8 @@ pub struct Circle<H, V, LengthOrPercentage> {
 
 /// <https://drafts.csswg.org/css-shapes/#funcdef-ellipse>
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue)]
 pub struct Ellipse<H, V, LengthOrPercentage> {
     pub position: Position<H, V>,
     pub semiaxis_x: ShapeRadius<LengthOrPercentage>,
@@ -93,8 +97,8 @@ pub struct Ellipse<H, V, LengthOrPercentage> {
 
 /// <https://drafts.csswg.org/css-shapes/#typedef-shape-radius>
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum ShapeRadius<LengthOrPercentage> {
     Length(LengthOrPercentage),
     #[animation(error)]
@@ -106,7 +110,8 @@ pub enum ShapeRadius<LengthOrPercentage> {
 /// A generic type for representing the `polygon()` function
 ///
 /// <https://drafts.csswg.org/css-shapes/#funcdef-polygon>
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct Polygon<LengthOrPercentage> {
     /// The filling rule for a polygon.
     pub fill: FillRule,
@@ -120,7 +125,8 @@ pub struct Polygon<LengthOrPercentage> {
 // says that it can also be `inherit`
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum FillRule {
     Nonzero,
     Evenodd,
diff --git a/components/style/values/generics/border.rs b/components/style/values/generics/border.rs
index e4442ffdc51..79c8713bfba 100644
--- a/components/style/values/generics/border.rs
+++ b/components/style/values/generics/border.rs
@@ -10,7 +10,8 @@ use values::generics::rect::Rect;
 use values::generics::size::Size;
 
 /// A generic value for a single side of a `border-image-width` property.
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum BorderImageSideWidth<LengthOrPercentage, Number> {
     /// `<length-or-percentage>`
     Length(LengthOrPercentage),
@@ -21,7 +22,8 @@ pub enum BorderImageSideWidth<LengthOrPercentage, Number> {
 }
 
 /// A generic value for the `border-image-slice` property.
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct BorderImageSlice<NumberOrPercentage> {
     /// The offsets.
     pub offsets: Rect<NumberOrPercentage>,
@@ -30,8 +32,8 @@ pub struct BorderImageSlice<NumberOrPercentage> {
 }
 
 /// A generic value for the `border-*-radius` longhand properties.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub struct BorderCornerRadius<L>(#[css(field_bound)] pub Size<L>);
 
 impl<L> BorderCornerRadius<L> {
@@ -42,8 +44,9 @@ impl<L> BorderCornerRadius<L> {
 }
 
 /// A generic value for the `border-spacing` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub struct BorderSpacing<L>(#[css(field_bound)] pub Size<L>);
 
 impl<L> BorderSpacing<L> {
@@ -56,8 +59,8 @@ impl<L> BorderSpacing<L> {
 /// A generic value for `border-radius`, `outline-radius` and `inset()`.
 ///
 /// <https://drafts.csswg.org/css-backgrounds-3/#border-radius>
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue)]
 pub struct BorderRadius<LengthOrPercentage> {
     /// The top left radius.
     pub top_left: BorderCornerRadius<LengthOrPercentage>,
diff --git a/components/style/values/generics/box.rs b/components/style/values/generics/box.rs
index 3c780ea9899..ea79e98eefb 100644
--- a/components/style/values/generics/box.rs
+++ b/components/style/values/generics/box.rs
@@ -7,8 +7,8 @@
 use values::animated::ToAnimatedZero;
 
 /// A generic value for the `vertical-align` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum VerticalAlign<LengthOrPercentage> {
     /// `baseline`
     Baseline,
@@ -48,7 +48,8 @@ impl<L> ToAnimatedZero for VerticalAlign<L> {
 }
 
 /// https://drafts.csswg.org/css-animations/#animation-iteration-count
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum AnimationIterationCount<Number> {
     /// A `<number>` value.
     Number(Number),
@@ -57,8 +58,9 @@ pub enum AnimationIterationCount<Number> {
 }
 
 /// A generic value for the `perspective` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub enum Perspective<NonNegativeLength> {
     /// A non-negative length.
     Length(NonNegativeLength),
diff --git a/components/style/values/generics/column.rs b/components/style/values/generics/column.rs
index 936349b8786..1d76f6cb552 100644
--- a/components/style/values/generics/column.rs
+++ b/components/style/values/generics/column.rs
@@ -5,8 +5,9 @@
 //! Generic types for the column properties.
 
 /// A generic type for `column-count` values.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub enum ColumnCount<PositiveInteger> {
     /// A positive integer.
     Integer(PositiveInteger),
diff --git a/components/style/values/generics/counters.rs b/components/style/values/generics/counters.rs
index e47a120b1d5..037834abf6e 100644
--- a/components/style/values/generics/counters.rs
+++ b/components/style/values/generics/counters.rs
@@ -11,7 +11,8 @@ use style_traits::{CssWriter, ToCss};
 use values::CustomIdent;
 
 /// A generic value for the `counter-increment` property.
-#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct CounterIncrement<I>(Counters<I>);
 
 impl<I> CounterIncrement<I> {
@@ -32,7 +33,8 @@ impl<I> Deref for CounterIncrement<I> {
 }
 
 /// A generic value for the `counter-reset` property.
-#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct CounterReset<I>(Counters<I>);
 
 impl<I> CounterReset<I> {
@@ -55,7 +57,8 @@ impl<I> Deref for CounterReset<I> {
 /// A generic value for lists of counters.
 ///
 /// Keyword `none` is represented by an empty vector.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct Counters<I>(Box<[(CustomIdent, I)]>);
 
 impl<I> Default for Counters<I> {
diff --git a/components/style/values/generics/effects.rs b/components/style/values/generics/effects.rs
index e306699eeb2..136f45635c1 100644
--- a/components/style/values/generics/effects.rs
+++ b/components/style/values/generics/effects.rs
@@ -10,7 +10,8 @@ use style_traits::values::{CssWriter, SequenceWriter, ToCss};
 use values::specified::url::SpecifiedUrl;
 
 /// A generic value for a single `box-shadow`.
-#[derive(Animate, Clone, Debug, MallocSizeOf, PartialEq, ToAnimatedValue, ToAnimatedZero)]
+#[derive(Animate, Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToAnimatedValue, ToAnimatedZero)]
 pub struct BoxShadow<Color, SizeLength, BlurShapeLength, ShapeLength> {
     /// The base shadow.
     pub base: SimpleShadow<Color, SizeLength, BlurShapeLength>,
@@ -23,8 +24,8 @@ pub struct BoxShadow<Color, SizeLength, BlurShapeLength, ShapeLength> {
 
 /// A generic value for a single `filter`.
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToComputedValue, ToCss)]
 pub enum Filter<Angle, Factor, Length, DropShadow> {
     /// `blur(<length>)`
     #[css(function)]
@@ -66,8 +67,8 @@ pub enum Filter<Angle, Factor, Length, DropShadow> {
 ///
 /// Contrary to the canonical order from the spec, the color is serialised
 /// first, like in Gecko and Webkit.
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToCss)]
 pub struct SimpleShadow<Color, SizeLength, ShapeLength> {
     /// Color.
     pub color: Color,
diff --git a/components/style/values/generics/flex.rs b/components/style/values/generics/flex.rs
index e1747410f12..1ab53233c44 100644
--- a/components/style/values/generics/flex.rs
+++ b/components/style/values/generics/flex.rs
@@ -6,8 +6,9 @@
 
 /// A generic value for the `flex-basis` property.
 #[cfg_attr(feature = "servo", derive(MallocSizeOf))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToComputedValue,
+         ToCss)]
 pub enum FlexBasis<Width> {
     /// `content`
     Content,
diff --git a/components/style/values/generics/font.rs b/components/style/values/generics/font.rs
index cbcd64502c4..738a40a7844 100644
--- a/components/style/values/generics/font.rs
+++ b/components/style/values/generics/font.rs
@@ -11,11 +11,12 @@ use num_traits::One;
 use parser::{Parse, ParserContext};
 use std::fmt::{self, Write};
 use std::io::Cursor;
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 use values::distance::{ComputeSquaredDistance, SquaredDistance};
 
 /// https://drafts.csswg.org/css-fonts-4/#feature-tag-value
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct FeatureTagValue<Integer> {
     /// A four-character tag, packed into a u32 (one byte per character).
     pub tag: FontTag,
@@ -45,7 +46,8 @@ where
 /// Variation setting for a single feature, see:
 ///
 /// https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
-#[derive(Animate, Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct VariationValue<Number> {
     /// A four-character tag, packed into a u32 (one byte per character).
     #[animation(constant)]
@@ -69,7 +71,8 @@ where
 
 /// A value both for font-variation-settings and font-feature-settings.
 #[css(comma)]
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct FontSettings<T>(#[css(if_empty = "normal", iterable)] pub Box<[T]>);
 
 impl<T> FontSettings<T> {
@@ -105,7 +108,8 @@ impl<T: Parse> Parse for FontSettings<T> {
 ///   https://drafts.csswg.org/css-fonts-4/#font-variation-settings-def
 ///   https://drafts.csswg.org/css-fonts-4/#descdef-font-face-font-feature-settings
 ///
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct FontTag(pub u32);
 
 impl ToCss for FontTag {
@@ -177,9 +181,13 @@ where
     }
 }
 
+impl<Length> SpecifiedValueInfo for KeywordInfo<Length> {
+    const SUPPORTED_TYPES: u8 = <KeywordSize as SpecifiedValueInfo>::SUPPORTED_TYPES;
+}
+
 /// CSS font keywords
 #[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero)]
+         ToAnimatedValue, ToAnimatedZero, SpecifiedValueInfo)]
 #[allow(missing_docs)]
 pub enum KeywordSize {
     XXSmall,
diff --git a/components/style/values/generics/gecko.rs b/components/style/values/generics/gecko.rs
index 1591afbfd97..72a8b71d073 100644
--- a/components/style/values/generics/gecko.rs
+++ b/components/style/values/generics/gecko.rs
@@ -7,7 +7,8 @@
 
 /// A generic value for scroll snap points.
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToComputedValue,
+         ToCss)]
 pub enum ScrollSnapPoint<LengthOrPercentage> {
     /// `none`
     None,
diff --git a/components/style/values/generics/grid.rs b/components/style/values/generics/grid.rs
index eae06fe58b4..d805fb5e0d0 100644
--- a/components/style/values/generics/grid.rs
+++ b/components/style/values/generics/grid.rs
@@ -18,7 +18,8 @@ use values::specified::grid::parse_line_names;
 /// A `<grid-line>` type.
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-grid-row-start-grid-line>
-#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct GridLine<Integer> {
     /// Flag to check whether it's a `span` keyword.
     pub is_span: bool,
@@ -148,7 +149,8 @@ impl Parse for GridLine<specified::Integer> {
 
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum TrackKeyword {
     Auto,
     MaxContent,
@@ -159,7 +161,8 @@ pub enum TrackKeyword {
 /// avoid re-implementing it for the computed type.
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-track-breadth>
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum TrackBreadth<L> {
     /// The generic type is almost always a non-negative `<length-percentage>`
     Breadth(L),
@@ -187,7 +190,7 @@ impl<L> TrackBreadth<L> {
 /// generic only to avoid code bloat. It only takes `<length-percentage>`
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-track-size>
-#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo)]
 pub enum TrackSize<L> {
     /// A flexible `<track-breadth>`
     Breadth(TrackBreadth<L>),
@@ -343,7 +346,8 @@ where
 /// The initial argument of the `repeat` function.
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-track-repeat>
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum RepeatCount<Integer> {
     /// A positive integer. This is allowed only for `<track-repeat>` and `<fixed-repeat>`
     Number(Integer),
@@ -378,7 +382,8 @@ impl Parse for RepeatCount<specified::Integer> {
 ///
 /// It can also hold `repeat()` function parameters, which expands into the respective
 /// values in its computed form.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct TrackRepeat<L, I> {
     /// The number of times for the value to be repeated (could also be `auto-fit` or `auto-fill`)
     pub count: RepeatCount<I>,
@@ -464,7 +469,8 @@ impl<L: Clone> TrackRepeat<L, specified::Integer> {
 }
 
 /// Track list values. Can be <track-size> or <track-repeat>
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum TrackListValue<LengthOrPercentage, Integer> {
     /// A <track-size> value.
     TrackSize(TrackSize<LengthOrPercentage>),
@@ -475,7 +481,8 @@ pub enum TrackListValue<LengthOrPercentage, Integer> {
 /// The type of a `<track-list>` as determined during parsing.
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-track-list>
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub enum TrackListType {
     /// [`<auto-track-list>`](https://drafts.csswg.org/css-grid/#typedef-auto-track-list)
     ///
@@ -497,7 +504,7 @@ pub enum TrackListType {
 /// A grid `<track-list>` type.
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-track-list>
-#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo)]
 pub struct TrackList<LengthOrPercentage, Integer> {
     /// The type of this `<track-list>` (auto, explicit or general).
     ///
@@ -569,7 +576,8 @@ impl<L: ToCss, I: ToCss> ToCss for TrackList<L, I> {
 ///
 /// `subgrid [ <line-names> | repeat(<positive-integer> | auto-fill, <line-names>+) ]+`
 /// Old spec: https://www.w3.org/TR/2015/WD-css-grid-1-20150917/#typedef-line-name-list
-#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, Default, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct LineNameList {
     /// The optional `<line-name-list>`
     pub names: Box<[Box<[CustomIdent]>]>,
@@ -672,7 +680,8 @@ impl ToCss for LineNameList {
 /// Variants for `<grid-template-rows> | <grid-template-columns>`
 /// Subgrid deferred to Level 2 spec due to lack of implementation.
 /// But it's implemented in gecko, so we have to as well.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum GridTemplateComponent<L, I> {
     /// `none` value.
     None,
diff --git a/components/style/values/generics/image.rs b/components/style/values/generics/image.rs
index 2cbb8b14112..4501f94433f 100644
--- a/components/style/values/generics/image.rs
+++ b/components/style/values/generics/image.rs
@@ -16,7 +16,7 @@ use values::serialize_atom_identifier;
 /// An [image].
 ///
 /// [image]: https://drafts.csswg.org/css-images/#image-values
-#[derive(Clone, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToComputedValue)]
 pub enum Image<Gradient, MozImageRect, ImageUrl> {
     /// A `<url()>` image.
     Url(ImageUrl),
@@ -164,7 +164,8 @@ impl ToCss for PaintWorklet {
 /// `-moz-image-rect(<uri>, top, right, bottom, left);`
 #[allow(missing_docs)]
 #[css(comma, function)]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct MozImageRect<NumberOrPercentage, MozImageRectUrl> {
     pub url: MozImageRectUrl,
     pub top: NumberOrPercentage,
diff --git a/components/style/values/generics/mod.rs b/components/style/values/generics/mod.rs
index 03df2c69278..f47b2f29b89 100644
--- a/components/style/values/generics/mod.rs
+++ b/components/style/values/generics/mod.rs
@@ -79,7 +79,8 @@ impl SymbolsType {
 /// Since wherever <counter-style> is used, 'none' is a valid value as
 /// well, we combine them into one type to make code simpler.
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, Eq, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Eq, PartialEq, SpecifiedValueInfo, ToComputedValue,
+         ToCss)]
 pub enum CounterStyleOrNone {
     /// `none`
     None,
@@ -139,12 +140,14 @@ impl Parse for CounterStyleOrNone {
 
 /// A wrapper of Non-negative values.
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         PartialOrd, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, PartialOrd, SpecifiedValueInfo, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub struct NonNegative<T>(pub T);
 
 /// A wrapper of greater-than-or-equal-to-one values.
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         PartialOrd, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, PartialOrd, SpecifiedValueInfo, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub struct GreaterThanOrEqualToOne<T>(pub T);
diff --git a/components/style/values/generics/pointing.rs b/components/style/values/generics/pointing.rs
index f84e70b7bfa..9d9ec031225 100644
--- a/components/style/values/generics/pointing.rs
+++ b/components/style/values/generics/pointing.rs
@@ -9,8 +9,9 @@ use style_traits::{CssWriter, ToCss};
 use style_traits::cursor::CursorKind;
 
 /// A generic value for the `caret-color` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub enum CaretColor<Color> {
     /// An explicit color.
     Color(Color),
@@ -21,7 +22,8 @@ pub enum CaretColor<Color> {
 /// A generic value for the `cursor` property.
 ///
 /// https://drafts.csswg.org/css-ui/#cursor
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct Cursor<Image> {
     /// The parsed images for the cursor.
     pub images: Box<[Image]>,
@@ -54,7 +56,8 @@ impl<Image: ToCss> ToCss for Cursor<Image> {
 }
 
 /// A generic value for item of `image cursors`.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct CursorImage<ImageUrl, Number> {
     /// The url to parse images from.
     pub url: ImageUrl,
diff --git a/components/style/values/generics/position.rs b/components/style/values/generics/position.rs
index aef2d233fd5..67c167c41ab 100644
--- a/components/style/values/generics/position.rs
+++ b/components/style/values/generics/position.rs
@@ -6,8 +6,8 @@
 //! [`position`](https://drafts.csswg.org/css-backgrounds-3/#position)
 
 /// A generic type for representing a CSS [position](https://drafts.csswg.org/css-values/#position).
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedZero, ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedZero, ToComputedValue)]
 pub struct Position<H, V> {
     /// The horizontal component of position.
     pub horizontal: H,
@@ -26,8 +26,8 @@ impl<H, V> Position<H, V> {
 }
 
 /// A generic value for the `z-index` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedZero, ToComputedValue, ToCss)]
 pub enum ZIndex<Integer> {
     /// An integer value.
     Integer(Integer),
diff --git a/components/style/values/generics/rect.rs b/components/style/values/generics/rect.rs
index f45ac32ba91..fb67e48a395 100644
--- a/components/style/values/generics/rect.rs
+++ b/components/style/values/generics/rect.rs
@@ -11,8 +11,8 @@ use style_traits::{CssWriter, ParseError, ToCss};
 
 /// A CSS value made of four components, where its `ToCss` impl will try to
 /// serialize as few components as possible, like for example in `border-width`.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToComputedValue)]
 pub struct Rect<T>(pub T, pub T, pub T, pub T);
 
 impl<T> Rect<T> {
diff --git a/components/style/values/generics/size.rs b/components/style/values/generics/size.rs
index e3632c1075d..ad93b94e65e 100644
--- a/components/style/values/generics/size.rs
+++ b/components/style/values/generics/size.rs
@@ -8,7 +8,7 @@ use cssparser::Parser;
 use euclid::Size2D;
 use parser::ParserContext;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, ToCss};
 use values::animated::ToAnimatedValue;
 
 /// A generic size, for `border-*-radius` longhand properties, or
@@ -93,3 +93,7 @@ where
         ))
     }
 }
+
+impl<L: SpecifiedValueInfo> SpecifiedValueInfo for Size<L> {
+    const SUPPORTED_TYPES: u8 = L::SUPPORTED_TYPES;
+}
diff --git a/components/style/values/generics/svg.rs b/components/style/values/generics/svg.rs
index 7bc4c6b61eb..9246175068c 100644
--- a/components/style/values/generics/svg.rs
+++ b/components/style/values/generics/svg.rs
@@ -16,8 +16,8 @@ use values::distance::{ComputeSquaredDistance, SquaredDistance};
 ///
 /// <https://www.w3.org/TR/SVG2/painting.html#SpecifyingPaint>
 #[animation(no_bound(UrlPaintServer))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToComputedValue, ToCss)]
 pub struct SVGPaint<ColorType, UrlPaintServer> {
     /// The paint source
     pub kind: SVGPaintKind<ColorType, UrlPaintServer>,
@@ -31,8 +31,9 @@ pub struct SVGPaint<ColorType, UrlPaintServer> {
 /// to have a fallback, Gecko lets the context
 /// properties have a fallback as well.
 #[animation(no_bound(UrlPaintServer))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToComputedValue,
+         ToCss)]
 pub enum SVGPaintKind<ColorType, UrlPaintServer> {
     /// `none`
     #[animation(error)]
@@ -112,8 +113,8 @@ impl<ColorType: Parse, UrlPaintServer: Parse> Parse for SVGPaint<ColorType, UrlP
 
 /// A value of <length> | <percentage> | <number> for svg which allow unitless length.
 /// <https://www.w3.org/TR/SVG11/painting.html#StrokeProperties>
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToAnimatedValue, ToAnimatedZero,
-         ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
 pub enum SvgLengthOrPercentageOrNumber<LengthOrPercentage, Number> {
     /// <length> | <percentage>
     LengthOrPercentage(LengthOrPercentage),
@@ -190,8 +191,9 @@ impl<LengthOrPercentageType: Parse, NumberType: Parse> Parse
 }
 
 /// An SVG length value supports `context-value` in addition to length.
-#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToComputedValue,
+         ToCss)]
 pub enum SVGLength<LengthType> {
     /// `<length> | <percentage> | <number>`
     Length(LengthType),
@@ -200,8 +202,8 @@ pub enum SVGLength<LengthType> {
 }
 
 /// Generic value for stroke-dasharray.
-#[derive(Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToComputedValue, ToCss)]
 pub enum SVGStrokeDashArray<LengthType> {
     /// `[ <length> | <percentage> | <number> ]#`
     #[css(comma)]
@@ -216,8 +218,8 @@ pub enum SVGStrokeDashArray<LengthType> {
 
 /// An SVG opacity value accepts `context-{fill,stroke}-opacity` in
 /// addition to opacity value.
-#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq, ToAnimatedZero,
-         ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedZero, ToComputedValue, ToCss)]
 pub enum SVGOpacity<OpacityType> {
     /// `<opacity-value>`
     Opacity(OpacityType),
diff --git a/components/style/values/generics/text.rs b/components/style/values/generics/text.rs
index 28a0adc385a..6cc5caaac77 100644
--- a/components/style/values/generics/text.rs
+++ b/components/style/values/generics/text.rs
@@ -12,7 +12,8 @@ use values::animated::{Animate, Procedure, ToAnimatedZero};
 use values::distance::{ComputeSquaredDistance, SquaredDistance};
 
 /// A generic value for the `initial-letter` property.
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum InitialLetter<Number, Integer> {
     /// `normal`
     Normal,
@@ -29,7 +30,8 @@ impl<N, I> InitialLetter<N, I> {
 }
 
 /// A generic spacing value for the `letter-spacing` and `word-spacing` properties.
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum Spacing<Value> {
     /// `normal`
     Normal,
@@ -110,8 +112,8 @@ where
 }
 
 /// A generic value for the `line-height` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToCss)]
 pub enum LineHeight<Number, LengthOrPercentage> {
     /// `normal`
     Normal,
@@ -140,8 +142,9 @@ impl<N, L> LineHeight<N, L> {
 }
 
 /// A generic value for the `-moz-tab-size` property.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+         ToComputedValue, ToCss)]
 pub enum MozTabSize<Number, Length> {
     /// A number.
     Number(Number),
diff --git a/components/style/values/generics/transform.rs b/components/style/values/generics/transform.rs
index 7c82eea5e1c..2c671541ea4 100644
--- a/components/style/values/generics/transform.rs
+++ b/components/style/values/generics/transform.rs
@@ -15,7 +15,8 @@ use values::specified::length::LengthOrPercentage as SpecifiedLengthOrPercentage
 
 /// A generic 2D transformation matrix.
 #[allow(missing_docs)]
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 #[css(comma, function)]
 pub struct Matrix<T> {
     pub a: T,
@@ -29,7 +30,8 @@ pub struct Matrix<T> {
 #[allow(missing_docs)]
 #[cfg_attr(rustfmt, rustfmt_skip)]
 #[css(comma, function = "matrix3d")]
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct Matrix3D<T> {
     pub m11: T, pub m12: T, pub m13: T, pub m14: T,
     pub m21: T, pub m22: T, pub m23: T, pub m24: T,
@@ -64,8 +66,8 @@ impl<T: Into<f64>> From<Matrix3D<T>> for Transform3D<f64> {
 }
 
 /// A generic transform origin.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedZero, ToComputedValue, ToCss)]
 pub struct TransformOrigin<H, V, Depth> {
     /// The horizontal origin.
     pub horizontal: H,
@@ -157,7 +159,8 @@ impl TimingKeyword {
     }
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// A single operation in the list of a `transform` value
 pub enum TransformOperation<Angle, Number, Length, Integer, LengthOrPercentage> {
     /// Represents a 2D 2x3 matrix.
@@ -261,7 +264,8 @@ pub enum TransformOperation<Angle, Number, Length, Integer, LengthOrPercentage>
     },
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// A value of the `transform` property
 pub struct Transform<T>(#[css(if_empty = "none", iterable)] pub Vec<T>);
 
@@ -554,8 +558,8 @@ pub fn get_normalized_vector_and_angle<T: Zero>(
     }
 }
 
-#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq, ToAnimatedZero,
-         ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedZero, ToComputedValue, ToCss)]
 /// A value of the `Rotate` property
 ///
 /// <https://drafts.csswg.org/css-transforms-2/#individual-transforms>
@@ -568,8 +572,8 @@ pub enum Rotate<Number, Angle> {
     Rotate3D(Number, Number, Number, Angle),
 }
 
-#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq, ToAnimatedZero,
-         ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedZero, ToComputedValue, ToCss)]
 /// A value of the `Scale` property
 ///
 /// <https://drafts.csswg.org/css-transforms-2/#individual-transforms>
@@ -584,8 +588,8 @@ pub enum Scale<Number> {
     Scale3D(Number, Number, Number),
 }
 
-#[derive(Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedZero,
-         ToComputedValue, ToCss)]
+#[derive(Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedZero, ToComputedValue, ToCss)]
 /// A value of the `Translate` property
 ///
 /// <https://drafts.csswg.org/css-transforms-2/#individual-transforms>
@@ -601,7 +605,8 @@ pub enum Translate<LengthOrPercentage, Length> {
 }
 
 #[allow(missing_docs)]
-#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum TransformStyle {
     #[cfg(feature = "servo")]
     Auto,
diff --git a/components/style/values/generics/url.rs b/components/style/values/generics/url.rs
index a05c28b1f46..5da74a7b087 100644
--- a/components/style/values/generics/url.rs
+++ b/components/style/values/generics/url.rs
@@ -9,8 +9,9 @@ use parser::{Parse, ParserContext};
 use style_traits::ParseError;
 
 /// An image url or none, used for example in list-style-image
-#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToComputedValue,
+         ToCss)]
 pub enum UrlOrNone<Url> {
     /// `none`
     None,
diff --git a/components/style/values/mod.rs b/components/style/values/mod.rs
index 2f4104a08b0..a61b774bdbf 100644
--- a/components/style/values/mod.rs
+++ b/components/style/values/mod.rs
@@ -93,8 +93,9 @@ impl Parse for Impossible {
 }
 
 /// A struct representing one of two kinds of values.
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, MallocSizeOf, PartialEq, ToAnimatedValue,
-         ToAnimatedZero, ToComputedValue, ToCss)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero, ToComputedValue,
+         ToCss)]
 pub enum Either<A, B> {
     /// The first value.
     First(A),
@@ -125,7 +126,8 @@ impl<A: Parse, B: Parse> Parse for Either<A, B> {
 }
 
 /// <https://drafts.csswg.org/css-values-4/#custom-idents>
-#[derive(Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct CustomIdent(pub Atom);
 
 impl CustomIdent {
@@ -160,7 +162,7 @@ impl ToCss for CustomIdent {
 }
 
 /// <https://drafts.csswg.org/css-animations/#typedef-keyframes-name>
-#[derive(Clone, Debug, MallocSizeOf, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, ToComputedValue, SpecifiedValueInfo)]
 pub enum KeyframesName {
     /// <custom-ident>
     Ident(CustomIdent),
diff --git a/components/style/values/specified/align.rs b/components/style/values/specified/align.rs
index 7b9b003a50c..a92ca52c8b4 100644
--- a/components/style/values/specified/align.rs
+++ b/components/style/values/specified/align.rs
@@ -16,7 +16,7 @@ bitflags! {
     /// Constants shared by multiple CSS Box Alignment properties
     ///
     /// These constants match Gecko's `NS_STYLE_ALIGN_*` constants.
-    #[derive(MallocSizeOf, ToComputedValue)]
+    #[derive(MallocSizeOf, SpecifiedValueInfo, ToComputedValue)]
     pub struct AlignFlags: u8 {
         // Enumeration stored in the lower 5 bits:
         /// 'auto'
@@ -135,7 +135,8 @@ pub enum AxisDirection {
 /// Shared value for the `align-content` and `justify-content` properties.
 ///
 /// <https://drafts.csswg.org/css-align/#content-distribution>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 pub struct ContentDistribution {
     primary: AlignFlags,
@@ -232,7 +233,8 @@ impl ContentDistribution {
 /// Value for the `align-content` property.
 ///
 /// <https://drafts.csswg.org/css-align/#propdef-align-content>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct AlignContent(pub ContentDistribution);
 
 impl Parse for AlignContent {
@@ -264,7 +266,8 @@ impl From<AlignContent> for u16 {
 /// Value for the `justify-content` property.
 ///
 /// <https://drafts.csswg.org/css-align/#propdef-align-content>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct JustifyContent(pub ContentDistribution);
 
 impl Parse for JustifyContent {
@@ -294,7 +297,8 @@ impl From<JustifyContent> for u16 {
 }
 
 /// <https://drafts.csswg.org/css-align/#self-alignment>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct SelfAlignment(pub AlignFlags);
 
 impl SelfAlignment {
@@ -344,7 +348,8 @@ impl SelfAlignment {
 /// The specified value of the align-self property.
 ///
 /// <https://drafts.csswg.org/css-align/#propdef-align-self>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct AlignSelf(pub SelfAlignment);
 
 impl Parse for AlignSelf {
@@ -374,7 +379,8 @@ impl From<AlignSelf> for u8 {
 /// The specified value of the justify-self property.
 ///
 /// <https://drafts.csswg.org/css-align/#propdef-justify-self>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct JustifySelf(pub SelfAlignment);
 
 impl Parse for JustifySelf {
@@ -404,7 +410,8 @@ impl From<JustifySelf> for u8 {
 /// Value of the `align-items` property
 ///
 /// <https://drafts.csswg.org/css-align/#self-alignment>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct AlignItems(pub AlignFlags);
 
 impl AlignItems {
@@ -443,7 +450,8 @@ impl Parse for AlignItems {
 /// Value of the `justify-items` property
 ///
 /// <https://drafts.csswg.org/css-align/#justify-items-property>
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 pub struct JustifyItems(pub AlignFlags);
 
 impl JustifyItems {
diff --git a/components/style/values/specified/angle.rs b/components/style/values/specified/angle.rs
index 3f49862e406..040ea9d9a7c 100644
--- a/components/style/values/specified/angle.rs
+++ b/components/style/values/specified/angle.rs
@@ -7,7 +7,7 @@
 use cssparser::{Parser, Token};
 use parser::{Parse, ParserContext};
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, ToCss};
 use values::CSSFloat;
 use values::computed::{Context, ToComputedValue};
 use values::computed::angle::Angle as ComputedAngle;
@@ -203,3 +203,5 @@ impl Angle {
         }.map_err(|()| input.new_unexpected_token_error(token.clone()))
     }
 }
+
+impl SpecifiedValueInfo for Angle {}
diff --git a/components/style/values/specified/background.rs b/components/style/values/specified/background.rs
index 88dbe8a158f..b9feb8b8e27 100644
--- a/components/style/values/specified/background.rs
+++ b/components/style/values/specified/background.rs
@@ -48,7 +48,8 @@ impl BackgroundSize {
 }
 
 /// One of the keywords for `background-repeat`.
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 #[allow(missing_docs)]
 pub enum BackgroundRepeatKeyword {
     Repeat,
@@ -60,7 +61,8 @@ pub enum BackgroundRepeatKeyword {
 /// The specified value for the `background-repeat` property.
 ///
 /// https://drafts.csswg.org/css-backgrounds/#the-background-repeat
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 pub enum BackgroundRepeat {
     /// `repeat-x`
     RepeatX,
diff --git a/components/style/values/specified/border.rs b/components/style/values/specified/border.rs
index 4b24b6bb6c4..0713ed99eb9 100644
--- a/components/style/values/specified/border.rs
+++ b/components/style/values/specified/border.rs
@@ -20,7 +20,7 @@ use values::specified::{AllowQuirks, Number, NumberOrPercentage};
 use values::specified::length::{Length, LengthOrPercentage, NonNegativeLength};
 
 /// A specified value for a single side of the `border-width` property.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum BorderSideWidth {
     /// `thin`
     Thin,
@@ -189,7 +189,8 @@ impl Parse for BorderSpacing {
 /// A single border-image-repeat keyword.
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToCss)]
 pub enum BorderImageRepeatKeyword {
     Stretch,
     Repeat,
@@ -200,7 +201,8 @@ pub enum BorderImageRepeatKeyword {
 /// The specified value for the `border-image-repeat` property.
 ///
 /// https://drafts.csswg.org/css-backgrounds/#the-border-image-repeat
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct BorderImageRepeat(pub BorderImageRepeatKeyword, pub BorderImageRepeatKeyword);
 
 impl ToCss for BorderImageRepeat {
diff --git a/components/style/values/specified/box.rs b/components/style/values/specified/box.rs
index 0609b6d8607..e26d82c8f67 100644
--- a/components/style/values/specified/box.rs
+++ b/components/style/values/specified/box.rs
@@ -9,9 +9,8 @@ use cssparser::Parser;
 use parser::{Parse, ParserContext};
 use selectors::parser::SelectorParseErrorKind;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
-use values::CustomIdent;
-use values::KeyframesName;
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, StyleParseErrorKind, ToCss};
+use values::{CustomIdent, KeyframesName};
 use values::generics::box_::AnimationIterationCount as GenericAnimationIterationCount;
 use values::generics::box_::Perspective as GenericPerspective;
 use values::generics::box_::VerticalAlign as GenericVerticalAlign;
@@ -19,7 +18,8 @@ use values::specified::{AllowQuirks, Number};
 use values::specified::length::{LengthOrPercentage, NonNegativeLength};
 
 #[allow(missing_docs)]
-#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
 /// Defines an element’s display type, which consists of
 /// the two basic qualities of how an element generates boxes
@@ -296,7 +296,8 @@ impl AnimationIterationCount {
 }
 
 /// A value for the `animation-name` property.
-#[derive(Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, Eq, Hash, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct AnimationName(pub Option<KeyframesName>);
 
 impl AnimationName {
@@ -339,7 +340,8 @@ impl Parse for AnimationName {
 
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum ScrollSnapType {
     None,
     Mandatory,
@@ -348,7 +350,8 @@ pub enum ScrollSnapType {
 
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum OverscrollBehavior {
     Auto,
     Contain,
@@ -357,13 +360,15 @@ pub enum OverscrollBehavior {
 
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum OverflowClipBox {
     PaddingBox,
     ContentBox,
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// Provides a rendering hint to the user agent,
 /// stating what kinds of changes the author expects
 /// to perform on the element
@@ -488,6 +493,8 @@ impl Parse for TouchAction {
     }
 }
 
+impl SpecifiedValueInfo for TouchAction {}
+
 #[cfg(feature = "gecko")]
 impl_bitflags_conversions!(TouchAction);
 
@@ -598,6 +605,8 @@ impl Parse for Contain {
     }
 }
 
+impl SpecifiedValueInfo for Contain {}
+
 /// A specified value for the `perspective` property.
 pub type Perspective = GenericPerspective<NonNegativeLength>;
 
diff --git a/components/style/values/specified/calc.rs b/components/style/values/specified/calc.rs
index 45aa3b27145..06c1dba2955 100644
--- a/components/style/values/specified/calc.rs
+++ b/components/style/values/specified/calc.rs
@@ -9,7 +9,7 @@
 use cssparser::{AngleOrNumber, NumberOrPercentage, Parser, Token};
 use parser::ParserContext;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 use style_traits::values::specified::AllowedNumericType;
 use values::{CSSFloat, CSSInteger};
 use values::computed;
@@ -150,6 +150,8 @@ impl ToCss for CalcLengthOrPercentage {
     }
 }
 
+impl SpecifiedValueInfo for CalcLengthOrPercentage {}
+
 impl CalcNode {
     /// Tries to parse a single element in the expression, that is, a
     /// `<length>`, `<angle>`, `<time>`, `<percentage>`, according to
diff --git a/components/style/values/specified/color.rs b/components/style/values/specified/color.rs
index 7038dbd299d..32e0316f654 100644
--- a/components/style/values/specified/color.rs
+++ b/components/style/values/specified/color.rs
@@ -14,7 +14,8 @@ use parser::{Parse, ParserContext};
 use properties::longhands::system_colors::SystemColor;
 use std::fmt::{self, Write};
 use std::io::Write as IoWrite;
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss, ValueParseErrorKind};
+use style_traits::{CssType, CssWriter, ParseError, StyleParseErrorKind};
+use style_traits::{SpecifiedValueInfo, ToCss, ValueParseErrorKind};
 use super::AllowQuirks;
 use values::computed::{Color as ComputedColor, Context, ToComputedValue};
 use values::specified::calc::CalcNode;
@@ -394,7 +395,7 @@ impl ToComputedValue for Color {
 
 /// Specified color value, but resolved to just RGBA for computed value
 /// with value from color property at the same context.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub struct RGBAColor(pub Color);
 
 impl Parse for RGBAColor {
@@ -426,10 +427,14 @@ impl From<Color> for RGBAColor {
     }
 }
 
+impl SpecifiedValueInfo for Color {
+    const SUPPORTED_TYPES: u8 = CssType::COLOR;
+}
+
 /// Specified value for the "color" property, which resolves the `currentcolor`
 /// keyword to the parent color instead of self's color.
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, PartialEq, ToCss)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 pub struct ColorPropertyValue(pub Color);
 
 impl ToComputedValue for ColorPropertyValue {
diff --git a/components/style/values/specified/counters.rs b/components/style/values/specified/counters.rs
index 996c1becda8..8a8e25ab065 100644
--- a/components/style/values/specified/counters.rs
+++ b/components/style/values/specified/counters.rs
@@ -99,7 +99,8 @@ fn is_decimal(counter_type: &CounterStyleType) -> bool {
 /// The specified value for the `content` property.
 ///
 /// https://drafts.csswg.org/css-content/#propdef-content
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum Content {
     /// `normal` reserved keyword.
     Normal,
@@ -113,7 +114,8 @@ pub enum Content {
 }
 
 /// Items for the `content` property.
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum ContentItem {
     /// Literal string content.
     String(Box<str>),
diff --git a/components/style/values/specified/effects.rs b/components/style/values/specified/effects.rs
index cb37972ad76..86464f1ba0c 100644
--- a/components/style/values/specified/effects.rs
+++ b/components/style/values/specified/effects.rs
@@ -35,7 +35,7 @@ pub type Filter = GenericFilter<Angle, Factor, NonNegativeLength, SimpleShadow>;
 pub type Filter = GenericFilter<Angle, Factor, NonNegativeLength, Impossible>;
 
 /// A value for the `<factor>` parts in `Filter`.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub struct Factor(NumberOrPercentage);
 
 impl Factor {
diff --git a/components/style/values/specified/font.rs b/components/style/values/specified/font.rs
index fa4d972ef16..3ecc04fcca2 100644
--- a/components/style/values/specified/font.rs
+++ b/components/style/values/specified/font.rs
@@ -77,7 +77,7 @@ 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, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum FontWeight {
     /// `<font-weight-absolute>`
     Absolute(AbsoluteFontWeight),
@@ -154,7 +154,7 @@ impl ToComputedValue for FontWeight {
 /// 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, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum AbsoluteFontWeight {
     /// A `<number>`, with the additional constraints specified in:
     ///
@@ -333,7 +333,8 @@ impl SpecifiedFontStyle {
 }
 
 /// The specified value of the `font-style` property.
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 #[allow(missing_docs)]
 pub enum FontStyle {
     Specified(SpecifiedFontStyle),
@@ -378,7 +379,8 @@ impl Parse for FontStyle {
 ///
 /// https://drafts.csswg.org/css-fonts-4/#font-stretch-prop
 #[allow(missing_docs)]
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 pub enum FontStretch {
     Stretch(Percentage),
     Keyword(FontStretchKeyword),
@@ -386,7 +388,8 @@ pub enum FontStretch {
 }
 
 /// A keyword value for `font-stretch`.
-#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 #[allow(missing_docs)]
 pub enum FontStretchKeyword {
     Normal,
@@ -501,7 +504,7 @@ impl ToComputedValue for FontStretch {
     }
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// A specified font-size value
 pub enum FontSize {
     /// A length; e.g. 10px.
@@ -602,6 +605,8 @@ impl Parse for FontFamily {
     }
 }
 
+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 {
@@ -619,7 +624,7 @@ impl Parse for FamilyName {
     }
 }
 
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Preserve the readability of text when font fallback occurs
 pub enum FontSizeAdjust {
     /// None variant
@@ -1079,7 +1084,7 @@ bitflags! {
     }
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Set of variant alternates
 pub enum VariantAlternates {
     /// Enables display of stylistic alternates
@@ -1104,7 +1109,7 @@ pub enum VariantAlternates {
     HistoricalForms,
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// List of Variant Alternates
 pub struct VariantAlternatesList(
     #[css(if_empty = "normal", iterable)] pub Box<[VariantAlternates]>,
@@ -1125,7 +1130,7 @@ impl VariantAlternatesList {
     }
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Control over the selection of these alternate glyphs
 pub enum FontVariantAlternates {
     /// Use alternative glyph from value
@@ -1346,6 +1351,8 @@ impl ToCss for VariantEastAsian {
 #[cfg(feature = "gecko")]
 impl_gecko_keyword_conversions!(VariantEastAsian, u16);
 
+impl SpecifiedValueInfo for VariantEastAsian {}
+
 /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
 #[cfg(feature = "gecko")]
 #[inline]
@@ -1376,7 +1383,7 @@ pub fn assert_variant_east_asian_matches() {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, PartialEq, ToCss)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Allows control of glyph substitution and sizing in East Asian text.
 pub enum FontVariantEastAsian {
     /// Value variant with `variant-east-asian`
@@ -1568,6 +1575,8 @@ impl ToCss for VariantLigatures {
     }
 }
 
+impl SpecifiedValueInfo for VariantLigatures {}
+
 #[cfg(feature = "gecko")]
 impl_gecko_keyword_conversions!(VariantLigatures, u16);
 
@@ -1601,7 +1610,7 @@ pub fn assert_variant_ligatures_matches() {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, PartialEq, ToCss)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Ligatures and contextual forms are ways of combining glyphs
 /// to produce more harmonized forms
 pub enum FontVariantLigatures {
@@ -1798,6 +1807,8 @@ impl ToCss for VariantNumeric {
     }
 }
 
+impl SpecifiedValueInfo for VariantNumeric {}
+
 #[cfg(feature = "gecko")]
 impl_gecko_keyword_conversions!(VariantNumeric, u8);
 
@@ -1830,7 +1841,7 @@ pub fn assert_variant_numeric_matches() {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, PartialEq, ToCss)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Specifies control over numerical forms.
 pub enum FontVariantNumeric {
     /// Value variant with `variant-numeric`
@@ -1938,7 +1949,7 @@ pub type SpecifiedFontFeatureSettings = FontSettings<FeatureTagValue<Integer>>;
 
 /// Define initial settings that apply when the font defined by an @font-face
 /// rule is rendered.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum FontFeatureSettings {
     /// Value of `FontSettings`
     Value(SpecifiedFontFeatureSettings),
@@ -1981,7 +1992,8 @@ impl Parse for FontFeatureSettings {
     }
 }
 
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 /// Whether user agents are allowed to synthesize bold or oblique font faces
 /// when a font family lacks bold or italic faces
 pub struct FontSynthesis {
@@ -2079,7 +2091,7 @@ impl From<FontSynthesis> for u8 {
     }
 }
 
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Allows authors to explicitly specify the language system of the font,
 /// overriding the language system implied by the content language
 pub enum FontLanguageOverride {
@@ -2169,7 +2181,7 @@ pub type SpecifiedFontVariationSettings = FontSettings<VariationValue<Number>>;
 
 /// Define initial settings that apply when the font defined by an @font-face
 /// rule is rendered.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum FontVariationSettings {
     /// Value of `FontSettings`
     Value(SpecifiedFontVariationSettings),
@@ -2254,7 +2266,8 @@ impl Parse for VariationValue<Number> {
     }
 }
 
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// text-zoom. Enable if true, disable if false
 pub struct XTextZoom(#[css(skip)] pub bool);
 
@@ -2271,7 +2284,8 @@ impl Parse for XTextZoom {
     }
 }
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// Internal property that reflects the lang attribute
 pub struct XLang(#[css(skip)] pub Atom);
 
@@ -2297,7 +2311,7 @@ impl Parse for XLang {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Specifies the minimum font size allowed due to changes in scriptlevel.
 /// Ref: https://wiki.mozilla.org/MathML:mstyle
 pub struct MozScriptMinSize(pub NoCalcLength);
@@ -2324,7 +2338,7 @@ impl Parse for MozScriptMinSize {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 /// Changes the scriptlevel in effect for the children.
 /// Ref: https://wiki.mozilla.org/MathML:mstyle
 ///
@@ -2359,7 +2373,8 @@ impl Parse for MozScriptLevel {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Copy, Debug, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToComputedValue,
+         ToCss)]
 /// Specifies the multiplier to be used to adjust font size
 /// due to changes in scriptlevel.
 ///
diff --git a/components/style/values/specified/grid.rs b/components/style/values/specified/grid.rs
index bbf2596f34c..830cccaf2e2 100644
--- a/components/style/values/specified/grid.rs
+++ b/components/style/values/specified/grid.rs
@@ -104,7 +104,7 @@ pub fn parse_line_names<'i, 't>(
 /// The type of `repeat` function (only used in parsing).
 ///
 /// <https://drafts.csswg.org/css-grid/#typedef-track-repeat>
-#[derive(Clone, Copy, Debug, PartialEq)]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo)]
 #[cfg_attr(feature = "servo", derive(MallocSizeOf))]
 enum RepeatType {
     /// [`<auto-repeat>`](https://drafts.csswg.org/css-grid/#typedef-auto-repeat)
diff --git a/components/style/values/specified/image.rs b/components/style/values/specified/image.rs
index dd5cdc90823..854dc38edb6 100644
--- a/components/style/values/specified/image.rs
+++ b/components/style/values/specified/image.rs
@@ -17,7 +17,8 @@ use servo_url::ServoUrl;
 use std::cmp::Ordering;
 use std::f32::consts::PI;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssType, CssWriter, ParseError, StyleParseErrorKind};
+use style_traits::{SpecifiedValueInfo, ToCss};
 use values::{Either, None_};
 #[cfg(feature = "gecko")]
 use values::computed::{Context, Position as ComputedPosition, ToComputedValue};
@@ -54,6 +55,10 @@ pub type Gradient = generic::Gradient<
     Angle,
 >;
 
+impl SpecifiedValueInfo for Gradient {
+    const SUPPORTED_TYPES: u8 = CssType::GRADIENT;
+}
+
 /// A specified gradient kind.
 #[cfg(not(feature = "gecko"))]
 pub type GradientKind =
diff --git a/components/style/values/specified/inherited_box.rs b/components/style/values/specified/inherited_box.rs
index 84c0ed12e74..da8da7614be 100644
--- a/components/style/values/specified/inherited_box.rs
+++ b/components/style/values/specified/inherited_box.rs
@@ -15,7 +15,7 @@ use values::specified::Angle;
 
 /// The specified value of the `image-orientation` property.
 /// https://drafts.csswg.org/css-images/#propdef-image-orientation
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo)]
 pub struct ImageOrientation {
     /// The angle specified, if any
     pub angle: Option<Angle>,
diff --git a/components/style/values/specified/length.rs b/components/style/values/specified/length.rs
index ec736718f0b..27206a40969 100644
--- a/components/style/values/specified/length.rs
+++ b/components/style/values/specified/length.rs
@@ -13,7 +13,7 @@ use font_metrics::FontMetricsQueryResult;
 use parser::{Parse, ParserContext};
 use std::cmp;
 use std::ops::{Add, Mul};
-use style_traits::{ParseError, StyleParseErrorKind};
+use style_traits::{ParseError, SpecifiedValueInfo, StyleParseErrorKind};
 use style_traits::values::specified::AllowedNumericType;
 use super::{AllowQuirks, Number, Percentage, ToComputedValue};
 use values::{Auto, CSSFloat, Either, Normal};
@@ -494,11 +494,13 @@ impl NoCalcLength {
     }
 }
 
+impl SpecifiedValueInfo for NoCalcLength {}
+
 /// An extension to `NoCalcLength` to parse `calc` expressions.
 /// This is commonly used for the `<length>` values.
 ///
 /// <https://drafts.csswg.org/css-values/#lengths>
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum Length {
     /// The internal length type that cannot parse `calc`
     NoCalc(NoCalcLength),
@@ -699,7 +701,7 @@ pub type NonNegativeLengthOrAuto = Either<NonNegativeLength, Auto>;
 
 /// A length or a percentage value.
 #[allow(missing_docs)]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum LengthOrPercentage {
     Length(NoCalcLength),
     Percentage(computed::Percentage),
@@ -845,7 +847,7 @@ impl LengthOrPercentage {
 
 /// Either a `<length>`, a `<percentage>`, or the `auto` keyword.
 #[allow(missing_docs)]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum LengthOrPercentageOrAuto {
     Length(NoCalcLength),
     Percentage(computed::Percentage),
@@ -1015,7 +1017,7 @@ impl Parse for NonNegativeLengthOrPercentageOrAuto {
 }
 
 /// Either a `<length>`, a `<percentage>`, or the `none` keyword.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 #[allow(missing_docs)]
 pub enum LengthOrPercentageOrNone {
     Length(NoCalcLength),
@@ -1195,7 +1197,7 @@ impl LengthOrNumber {
 ///
 /// Note that it only accepts non-negative values.
 #[allow(missing_docs)]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum MozLength {
     LengthOrPercentageOrAuto(LengthOrPercentageOrAuto),
     ExtremumLength(ExtremumLength),
@@ -1252,7 +1254,7 @@ impl MozLength {
 
 /// A value suitable for a `max-width` or `max-height` property.
 #[allow(missing_docs)]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum MaxLength {
     LengthOrPercentageOrNone(LengthOrPercentageOrNone),
     ExtremumLength(ExtremumLength),
diff --git a/components/style/values/specified/list.rs b/components/style/values/specified/list.rs
index 4930d3bcec6..89e4afda6fc 100644
--- a/components/style/values/specified/list.rs
+++ b/components/style/values/specified/list.rs
@@ -15,7 +15,8 @@ use values::generics::CounterStyleOrNone;
 
 /// Specified and computed `list-style-type` property.
 #[cfg(feature = "gecko")]
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub enum ListStyleType {
     /// <counter-style> | none
     CounterStyle(CounterStyleOrNone),
@@ -77,7 +78,8 @@ impl Parse for ListStyleType {
 ///
 /// FIXME(emilio): It's a shame that this allocates all the time it's computed,
 /// probably should just be refcounted.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct Quotes(pub Box<[(Box<str>, Box<str>)]>);
 
 impl ToCss for Quotes {
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index 20b49596ab7..9b4edfac413 100644
--- a/components/style/values/specified/mod.rs
+++ b/components/style/values/specified/mod.rs
@@ -13,7 +13,7 @@ use num_traits::One;
 use parser::{Parse, ParserContext};
 use std::f32;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 use style_traits::values::specified::AllowedNumericType;
 use super::{Auto, CSSFloat, CSSInteger, Either};
 use super::computed::{Context, ToComputedValue};
@@ -149,8 +149,8 @@ fn parse_number_with_clamping_mode<'i, 't>(
 // FIXME(emilio): Should move to border.rs
 #[allow(missing_docs)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Ord, Parse, PartialEq, PartialOrd,
-         ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Ord, Parse, PartialEq,
+         PartialOrd, SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum BorderStyle {
     None = -1,
     Solid = 6,
@@ -273,6 +273,8 @@ impl ToCss for Number {
     }
 }
 
+impl SpecifiedValueInfo for Number {}
+
 impl From<Number> for f32 {
     #[inline]
     fn from(n: Number) -> Self {
@@ -326,7 +328,8 @@ impl Parse for GreaterThanOrEqualToOneNumber {
 ///
 /// FIXME(emilio): Should probably use Either.
 #[allow(missing_docs)]
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 pub enum NumberOrPercentage {
     Percentage(Percentage),
     Number(Number),
@@ -364,7 +367,8 @@ impl Parse for NumberOrPercentage {
 }
 
 #[allow(missing_docs)]
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, PartialOrd, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, PartialOrd,
+         SpecifiedValueInfo, ToCss)]
 pub struct Opacity(Number);
 
 impl Parse for Opacity {
@@ -533,6 +537,8 @@ impl ToCss for Integer {
     }
 }
 
+impl SpecifiedValueInfo for Integer {}
+
 /// A wrapper of Integer, with value >= 1.
 pub type PositiveInteger = GreaterThanOrEqualToOne<Integer>;
 
@@ -562,7 +568,7 @@ pub type GridLine = GenericGridLine<Integer>;
 /// `<grid-template-rows> | <grid-template-columns>`
 pub type GridTemplateComponent = GenericGridTemplateComponent<LengthOrPercentage, Integer>;
 
-#[derive(Clone, Debug, MallocSizeOf, PartialEq)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo)]
 /// rect(<top>, <left>, <bottom>, <right>) used by clip and image-region
 pub struct ClipRect {
     /// <top> (<length> | <auto>)
@@ -846,3 +852,5 @@ impl ToCss for Attr {
         dest.write_str(")")
     }
 }
+
+impl SpecifiedValueInfo for Attr {}
diff --git a/components/style/values/specified/outline.rs b/components/style/values/specified/outline.rs
index 54494692d42..c3357f87ec2 100644
--- a/components/style/values/specified/outline.rs
+++ b/components/style/values/specified/outline.rs
@@ -10,8 +10,8 @@ use selectors::parser::SelectorParseErrorKind;
 use style_traits::ParseError;
 use values::specified::BorderStyle;
 
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Ord, PartialEq, PartialOrd, ToComputedValue,
-         ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Ord, PartialEq, PartialOrd,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 /// <https://drafts.csswg.org/css-ui/#propdef-outline-style>
 pub enum OutlineStyle {
     /// auto
diff --git a/components/style/values/specified/percentage.rs b/components/style/values/specified/percentage.rs
index d7f1424382f..9f8fb1bfbf5 100644
--- a/components/style/values/specified/percentage.rs
+++ b/components/style/values/specified/percentage.rs
@@ -7,7 +7,7 @@
 use cssparser::{Parser, Token};
 use parser::{Parse, ParserContext};
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, ToCss};
 use style_traits::values::specified::AllowedNumericType;
 use values::{serialize_percentage, CSSFloat};
 use values::computed::{Context, ToComputedValue};
@@ -158,3 +158,5 @@ impl ToComputedValue for Percentage {
         Percentage::new(computed.0)
     }
 }
+
+impl SpecifiedValueInfo for Percentage {}
diff --git a/components/style/values/specified/position.rs b/components/style/values/specified/position.rs
index d82240a3228..cb4b4aeb45b 100644
--- a/components/style/values/specified/position.rs
+++ b/components/style/values/specified/position.rs
@@ -34,7 +34,7 @@ pub type HorizontalPosition = PositionComponent<X>;
 pub type VerticalPosition = PositionComponent<Y>;
 
 /// The specified value of a component of a CSS `<position>`.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum PositionComponent<S> {
     /// `center`
     Center,
@@ -45,7 +45,8 @@ pub enum PositionComponent<S> {
 }
 
 /// A keyword for the X direction.
-#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 #[allow(missing_docs)]
 pub enum X {
     Left,
@@ -53,7 +54,8 @@ pub enum X {
 }
 
 /// A keyword for the Y direction.
-#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 #[allow(missing_docs)]
 pub enum Y {
     Top,
@@ -409,7 +411,8 @@ impl ToCss for LegacyPosition {
     }
 }
 
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// Auto-placement algorithm Option
 pub enum AutoFlow {
     /// The auto-placement algorithm places items by filling each row in turn,
@@ -420,7 +423,8 @@ pub enum AutoFlow {
     Column,
 }
 
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 /// Controls how the auto-placement algorithm works
 /// specifying exactly how auto-placed items get flowed into the grid
 pub struct GridAutoFlow {
@@ -533,7 +537,7 @@ impl From<GridAutoFlow> for u8 {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToComputedValue, ToCss)]
 /// https://drafts.csswg.org/css-grid/#named-grid-area
 pub struct TemplateAreas {
     /// `named area` containing for each template area
@@ -639,7 +643,8 @@ impl Parse for TemplateAreas {
 }
 
 /// Arc type for `Arc<TemplateAreas>`
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct TemplateAreasArc(#[ignore_malloc_size_of = "Arc"] pub Arc<TemplateAreas>);
 
 impl Parse for TemplateAreasArc {
@@ -654,7 +659,7 @@ impl Parse for TemplateAreasArc {
 }
 
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Debug, PartialEq)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo)]
 /// Not associated with any particular grid item, but can
 /// be referenced from the grid-placement properties.
 pub struct NamedArea {
diff --git a/components/style/values/specified/svg.rs b/components/style/values/specified/svg.rs
index 120f2bf821a..766f36cfc1e 100644
--- a/components/style/values/specified/svg.rs
+++ b/components/style/values/specified/svg.rs
@@ -173,7 +173,8 @@ const PAINT_ORDER_MASK: u8 = 0b11;
 ///
 /// Higher priority values, i.e. the values specified first,
 /// will be painted first (and may be covered by paintings of lower priority)
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct SVGPaintOrder(pub u8);
 
 impl SVGPaintOrder {
@@ -280,7 +281,8 @@ impl ToCss for SVGPaintOrder {
 
 /// Specified MozContextProperties value.
 /// Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-context-properties)
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct MozContextProperties(pub CustomIdent);
 
 impl Parse for MozContextProperties {
diff --git a/components/style/values/specified/table.rs b/components/style/values/specified/table.rs
index a03db90340c..085c9adc9d8 100644
--- a/components/style/values/specified/table.rs
+++ b/components/style/values/specified/table.rs
@@ -8,7 +8,8 @@ use cssparser::Parser;
 use parser::{Parse, ParserContext};
 use style_traits::{ParseError, StyleParseErrorKind};
 
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 /// span. for `<col span>` pres attr
 pub struct XSpan(#[css(skip)] pub i32);
 
diff --git a/components/style/values/specified/text.rs b/components/style/values/specified/text.rs
index fa8a7764ad8..d2ce18dcf3f 100644
--- a/components/style/values/specified/text.rs
+++ b/components/style/values/specified/text.rs
@@ -158,7 +158,7 @@ impl ToComputedValue for LineHeight {
 }
 
 /// A generic value for the `text-overflow` property.
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum TextOverflowSide {
     /// Clip inline content.
     Clip,
@@ -192,7 +192,7 @@ impl Parse for TextOverflowSide {
     }
 }
 
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 /// text-overflow. Specifies rendering when inline content overflows its line box edge.
 pub struct TextOverflow {
     /// First value. Applies to end line box edge if no second is supplied; line-left edge otherwise.
@@ -252,7 +252,7 @@ impl ToComputedValue for TextOverflow {
 }
 
 bitflags! {
-    #[derive(MallocSizeOf, ToComputedValue)]
+    #[derive(MallocSizeOf, SpecifiedValueInfo, ToComputedValue)]
     /// Specified keyword values for the text-decoration-line property.
     pub struct TextDecorationLine: u8 {
         /// No text decoration line is specified
@@ -357,7 +357,8 @@ impl Parse for TextDecorationLine {
 macro_rules! define_text_align_keyword {
     ($($name: ident => $discriminant: expr,)+) => {
         /// Specified value of text-align keyword value.
-        #[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+        #[derive(Clone, Copy, Debug, Eq, Hash, MallocSizeOf, Parse, PartialEq,
+                 SpecifiedValueInfo, ToComputedValue, ToCss)]
         #[allow(missing_docs)]
         pub enum TextAlignKeyword {
             $(
@@ -417,7 +418,7 @@ impl TextAlignKeyword {
 
 /// Specified value of text-align property.
 #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
+#[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, SpecifiedValueInfo)]
 pub enum TextAlign {
     /// Keyword value of text-align property.
     Keyword(TextAlignKeyword),
@@ -534,7 +535,7 @@ impl ToComputedValue for TextAlign {
 }
 
 /// Specified value of text-emphasis-style property.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum TextEmphasisStyle {
     /// <fill> <shape>
     Keyword(TextEmphasisKeywordValue),
@@ -545,7 +546,7 @@ pub enum TextEmphasisStyle {
 }
 
 /// Keyword value for the text-emphasis-style property
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum TextEmphasisKeywordValue {
     /// <fill>
     Fill(TextEmphasisFillMode),
@@ -574,7 +575,8 @@ impl TextEmphasisKeywordValue {
 }
 
 /// Fill mode for the text-emphasis-style property
-#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, Parse, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 pub enum TextEmphasisFillMode {
     /// `filled`
     Filled,
@@ -583,7 +585,8 @@ pub enum TextEmphasisFillMode {
 }
 
 /// Shape keyword for the text-emphasis-style property
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToCss)]
 pub enum TextEmphasisShapeKeyword {
     /// `dot`
     Dot,
@@ -709,7 +712,8 @@ impl Parse for TextEmphasisStyle {
 }
 
 /// The allowed horizontal values for the `text-emphasis-position` property.
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum TextEmphasisHorizontalWritingModeValue {
     /// Draw marks over the text in horizontal writing mode.
     Over,
@@ -718,7 +722,8 @@ pub enum TextEmphasisHorizontalWritingModeValue {
 }
 
 /// The allowed vertical values for the `text-emphasis-position` property.
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, Parse, PartialEq,
+         SpecifiedValueInfo, ToComputedValue, ToCss)]
 pub enum TextEmphasisVerticalWritingModeValue {
     /// Draws marks to the right of the text in vertical writing mode.
     Right,
@@ -727,7 +732,8 @@ pub enum TextEmphasisVerticalWritingModeValue {
 }
 
 /// Specified value of `text-emphasis-position` property.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue, ToCss)]
 pub struct TextEmphasisPosition(
     pub TextEmphasisHorizontalWritingModeValue,
     pub TextEmphasisVerticalWritingModeValue,
diff --git a/components/style/values/specified/time.rs b/components/style/values/specified/time.rs
index 7fa5c0a52a4..107c45b2d48 100644
--- a/components/style/values/specified/time.rs
+++ b/components/style/values/specified/time.rs
@@ -7,7 +7,7 @@
 use cssparser::{Parser, Token};
 use parser::{Parse, ParserContext};
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, ParseError, SpecifiedValueInfo, StyleParseErrorKind, ToCss};
 use style_traits::values::specified::AllowedNumericType;
 use values::CSSFloat;
 use values::computed::{Context, ToComputedValue};
@@ -165,3 +165,5 @@ impl ToCss for Time {
         Ok(())
     }
 }
+
+impl SpecifiedValueInfo for Time {}
diff --git a/components/style/values/specified/transform.rs b/components/style/values/specified/transform.rs
index 4f4ef1c73df..b66e5744f39 100644
--- a/components/style/values/specified/transform.rs
+++ b/components/style/values/specified/transform.rs
@@ -7,7 +7,7 @@
 use cssparser::Parser;
 use parser::{Parse, ParserContext};
 use selectors::parser::SelectorParseErrorKind;
-use style_traits::{ParseError, StyleParseErrorKind};
+use style_traits::{CssType, ParseError, SpecifiedValueInfo, StyleParseErrorKind};
 use values::computed::{Context, LengthOrPercentage as ComputedLengthOrPercentage};
 use values::computed::{Percentage as ComputedPercentage, ToComputedValue};
 use values::computed::transform::TimingFunction as ComputedTimingFunction;
@@ -233,7 +233,7 @@ impl Parse for Transform {
 }
 
 /// The specified value of a component of a CSS `<transform-origin>`.
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo, ToCss)]
 pub enum OriginComponent<S> {
     /// `center`
     Center,
@@ -246,6 +246,10 @@ pub enum OriginComponent<S> {
 /// A specified timing function.
 pub type TimingFunction = generic::TimingFunction<Integer, Number>;
 
+impl SpecifiedValueInfo for TimingFunction {
+    const SUPPORTED_TYPES: u8 = CssType::TIMING_FUNCTION;
+}
+
 impl Parse for TransformOrigin {
     fn parse<'i, 't>(
         context: &ParserContext,
diff --git a/components/style/values/specified/ui.rs b/components/style/values/specified/ui.rs
index b86bab0d81e..fc7ef048082 100644
--- a/components/style/values/specified/ui.rs
+++ b/components/style/values/specified/ui.rs
@@ -10,7 +10,8 @@ use std::fmt::{self, Write};
 use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
 
 /// Specified value of `-moz-force-broken-image-icon`
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct MozForceBrokenImageIcon(pub bool);
 
 impl MozForceBrokenImageIcon {
diff --git a/components/style_derive/animate.rs b/components/style_derive/animate.rs
index e54f1819c99..d591e3db108 100644
--- a/components/style_derive/animate.rs
+++ b/components/style_derive/animate.rs
@@ -68,7 +68,7 @@ pub fn derive(mut input: DeriveInput) -> Tokens {
 }
 
 fn derive_variant_arm(variant: &VariantInfo) -> Result<Tokens, ()> {
-    let variant_attrs = cg::parse_variant_attrs::<AnimationVariantAttrs>(&variant.ast());
+    let variant_attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
     if variant_attrs.error {
         return Err(());
     }
diff --git a/components/style_derive/cg.rs b/components/style_derive/cg.rs
index ff391c79180..b370a5c55d4 100644
--- a/components/style_derive/cg.rs
+++ b/components/style_derive/cg.rs
@@ -188,7 +188,7 @@ where
     }
 }
 
-pub fn parse_variant_attrs<A>(variant: &VariantAst) -> A
+pub fn parse_variant_attrs_from_ast<A>(variant: &VariantAst) -> A
 where
     A: FromVariant,
 {
@@ -198,7 +198,14 @@ where
         fields: variant.fields.clone(),
         discriminant: variant.discriminant.clone(),
     };
-    match A::from_variant(&v) {
+    parse_variant_attrs(&v)
+}
+
+pub fn parse_variant_attrs<A>(variant: &Variant) -> A
+where
+    A: FromVariant
+{
+    match A::from_variant(variant) {
         Ok(attrs) => attrs,
         Err(e) => panic!("failed to parse variant attributes: {}", e),
     }
diff --git a/components/style_derive/compute_squared_distance.rs b/components/style_derive/compute_squared_distance.rs
index 07408bbcddb..5b414206cda 100644
--- a/components/style_derive/compute_squared_distance.rs
+++ b/components/style_derive/compute_squared_distance.rs
@@ -26,7 +26,7 @@ pub fn derive(mut input: DeriveInput) -> Tokens {
         let mut append_error_clause = s.variants().len() > 1;
 
         let match_body = s.variants().iter().fold(quote!(), |body, variant| {
-            let attrs = cg::parse_variant_attrs::<AnimationVariantAttrs>(&variant.ast());
+            let attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
             if attrs.error {
                 append_error_clause = true;
                 return body;
diff --git a/components/style_derive/lib.rs b/components/style_derive/lib.rs
index e9d799fe9a9..86442070ca1 100644
--- a/components/style_derive/lib.rs
+++ b/components/style_derive/lib.rs
@@ -16,6 +16,7 @@ mod animate;
 mod cg;
 mod compute_squared_distance;
 mod parse;
+mod specified_value_info;
 mod to_animated_value;
 mod to_animated_zero;
 mod to_computed_value;
@@ -62,3 +63,9 @@ pub fn derive_to_css(stream: TokenStream) -> TokenStream {
     let input = syn::parse(stream).unwrap();
     to_css::derive(input).into()
 }
+
+#[proc_macro_derive(SpecifiedValueInfo, attributes(css))]
+pub fn derive_specified_value_info(stream: TokenStream) -> TokenStream {
+    let input = syn::parse(stream).unwrap();
+    specified_value_info::derive(input).into()
+}
diff --git a/components/style_derive/parse.rs b/components/style_derive/parse.rs
index fb429a05599..620ba3fee82 100644
--- a/components/style_derive/parse.rs
+++ b/components/style_derive/parse.rs
@@ -19,7 +19,7 @@ pub fn derive(input: DeriveInput) -> Tokens {
             "Parse is only supported for single-variant enums for now"
         );
 
-        let variant_attrs = cg::parse_variant_attrs::<CssVariantAttrs>(&variant.ast());
+        let variant_attrs = cg::parse_variant_attrs_from_ast::<CssVariantAttrs>(&variant.ast());
         let identifier = cg::to_css_identifier(
             &variant_attrs.keyword.unwrap_or(variant.ast().ident.as_ref().into()),
         );
diff --git a/components/style_derive/specified_value_info.rs b/components/style_derive/specified_value_info.rs
new file mode 100644
index 00000000000..be3e00f994b
--- /dev/null
+++ b/components/style_derive/specified_value_info.rs
@@ -0,0 +1,68 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+use cg;
+use quote::Tokens;
+use syn::{Data, DeriveInput, Fields};
+use to_css::{CssFieldAttrs, CssInputAttrs, CssVariantAttrs};
+
+pub fn derive(mut input: DeriveInput) -> Tokens {
+    let attrs = cg::parse_input_attrs::<CssInputAttrs>(&input);
+    let mut types_value = quote!(0);
+    // If the whole value is wrapped in a function, value types of its
+    // fields should not be propagated.
+    if attrs.function.is_none() {
+        let mut where_clause = input.generics.where_clause.take();
+        for param in input.generics.type_params() {
+            cg::add_predicate(
+                &mut where_clause,
+                parse_quote!(#param: ::style_traits::SpecifiedValueInfo),
+            );
+        }
+        input.generics.where_clause = where_clause;
+
+        match input.data {
+            Data::Enum(ref e) => {
+                for v in e.variants.iter() {
+                    let attrs = cg::parse_variant_attrs::<CssVariantAttrs>(&v);
+                    if attrs.function.is_none() {
+                        derive_struct_fields(&v.fields, &mut types_value);
+                    }
+                }
+            }
+            Data::Struct(ref s) => {
+                derive_struct_fields(&s.fields, &mut types_value)
+            }
+            Data::Union(_) => unreachable!("union is not supported"),
+        }
+    }
+
+    let name = &input.ident;
+    let (impl_generics, ty_generics, where_clause) = input.generics.split_for_impl();
+    quote! {
+        impl #impl_generics ::style_traits::SpecifiedValueInfo for #name #ty_generics
+        #where_clause
+        {
+            const SUPPORTED_TYPES: u8 = #types_value;
+        }
+    }
+}
+
+fn derive_struct_fields(fields: &Fields, supports_body: &mut Tokens) {
+    let fields = match *fields {
+        Fields::Unit => return,
+        Fields::Named(ref fields) => fields.named.iter(),
+        Fields::Unnamed(ref fields) => fields.unnamed.iter(),
+    };
+    supports_body.append_all(fields.map(|field| {
+        let attrs = cg::parse_field_attrs::<CssFieldAttrs>(field);
+        if attrs.skip {
+            return quote!();
+        }
+        let ty = &field.ty;
+        quote! {
+            | <#ty as ::style_traits::SpecifiedValueInfo>::SUPPORTED_TYPES
+        }
+    }));
+}
diff --git a/components/style_derive/to_animated_zero.rs b/components/style_derive/to_animated_zero.rs
index 9ee786f7ec8..00ddbd2cea6 100644
--- a/components/style_derive/to_animated_zero.rs
+++ b/components/style_derive/to_animated_zero.rs
@@ -22,7 +22,7 @@ pub fn derive(mut input: syn::DeriveInput) -> quote::Tokens {
     }
 
     let to_body = synstructure::Structure::new(&input).each_variant(|variant| {
-        let attrs = cg::parse_variant_attrs::<AnimationVariantAttrs>(&variant.ast());
+        let attrs = cg::parse_variant_attrs_from_ast::<AnimationVariantAttrs>(&variant.ast());
         if attrs.error {
             return Some(quote! { Err(()) });
         }
diff --git a/components/style_derive/to_css.rs b/components/style_derive/to_css.rs
index 4f8841810c1..148599586ed 100644
--- a/components/style_derive/to_css.rs
+++ b/components/style_derive/to_css.rs
@@ -75,7 +75,7 @@ fn derive_variant_arm(
     let bindings = variant.bindings();
     let identifier = cg::to_css_identifier(variant.ast().ident.as_ref());
     let ast = variant.ast();
-    let variant_attrs = cg::parse_variant_attrs::<CssVariantAttrs>(&ast);
+    let variant_attrs = cg::parse_variant_attrs_from_ast::<CssVariantAttrs>(&ast);
     let separator = if variant_attrs.comma { ", " } else { " " };
 
     if variant_attrs.dimension {
@@ -207,12 +207,12 @@ fn derive_single_field_expr(
 
 #[darling(attributes(css), default)]
 #[derive(Default, FromDeriveInput)]
-struct CssInputAttrs {
-    derive_debug: bool,
+pub struct CssInputAttrs {
+    pub derive_debug: bool,
     // Here because structs variants are also their whole type definition.
-    function: Option<Override<String>>,
+    pub function: Option<Override<String>>,
     // Here because structs variants are also their whole type definition.
-    comma: bool,
+    pub comma: bool,
 }
 
 #[darling(attributes(css), default)]
@@ -227,10 +227,10 @@ pub struct CssVariantAttrs {
 
 #[darling(attributes(css), default)]
 #[derive(Default, FromField)]
-struct CssFieldAttrs {
-    if_empty: Option<String>,
-    field_bound: bool,
-    iterable: bool,
-    skip: bool,
-    skip_if: Option<Path>,
+pub struct CssFieldAttrs {
+    pub if_empty: Option<String>,
+    pub field_bound: bool,
+    pub iterable: bool,
+    pub skip: bool,
+    pub skip_if: Option<Path>,
 }
diff --git a/components/style_traits/cursor.rs b/components/style_traits/cursor.rs
index 3ffd2814382..fb529496206 100644
--- a/components/style_traits/cursor.rs
+++ b/components/style_traits/cursor.rs
@@ -4,7 +4,7 @@
 
 //! A list of common mouse cursors per CSS3-UI § 8.1.1.
 
-use super::{CssWriter, ToCss};
+use super::{CssWriter, SpecifiedValueInfo, ToCss};
 
 macro_rules! define_cursor {
     (
@@ -57,6 +57,8 @@ macro_rules! define_cursor {
                 }
             }
         }
+
+        impl SpecifiedValueInfo for CursorKind {}
     }
 }
 
diff --git a/components/style_traits/lib.rs b/components/style_traits/lib.rs
index 3b7304b1aa7..bf7a9b59cd9 100644
--- a/components/style_traits/lib.rs
+++ b/components/style_traits/lib.rs
@@ -73,11 +73,13 @@ pub enum CSSPixel {}
 //     / desktop_zoom => CSSPixel
 
 pub mod cursor;
+pub mod specified_value_info;
 #[macro_use]
 pub mod values;
 #[macro_use]
 pub mod viewport;
 
+pub use specified_value_info::{CssType, SpecifiedValueInfo};
 pub use values::{Comma, CommaWithSpace, CssWriter, OneOrMoreSeparated, Separator, Space, ToCss};
 
 /// The error type for all CSS parsing routines.
diff --git a/components/style_traits/specified_value_info.rs b/components/style_traits/specified_value_info.rs
new file mode 100644
index 00000000000..d6bc5011483
--- /dev/null
+++ b/components/style_traits/specified_value_info.rs
@@ -0,0 +1,71 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+//! Value information for devtools.
+
+use servo_arc::Arc;
+use std::ops::Range;
+
+/// Type of value that a property supports. This is used by Gecko's
+/// devtools to make sense about value it parses, and types listed
+/// here should match TYPE_* constants in InspectorUtils.webidl.
+///
+/// XXX This should really be a bitflags rather than a namespace mod,
+/// but currently we cannot use bitflags in const.
+#[allow(non_snake_case)]
+pub mod CssType {
+    /// <color>
+    pub const COLOR: u8 = 1 << 0;
+    /// <gradient>
+    pub const GRADIENT: u8 = 1 << 1;
+    /// <timing-function>
+    pub const TIMING_FUNCTION: u8 = 1 << 2;
+}
+
+/// Information of values of a given specified value type.
+pub trait SpecifiedValueInfo {
+    /// Supported CssTypes by the given value type.
+    ///
+    /// XXX This should be typed CssType when that becomes a bitflags.
+    /// Currently we cannot do so since bitflags cannot be used in constant.
+    const SUPPORTED_TYPES: u8 = 0;
+}
+
+impl SpecifiedValueInfo for bool {}
+impl SpecifiedValueInfo for f32 {}
+impl SpecifiedValueInfo for i8 {}
+impl SpecifiedValueInfo for i32 {}
+impl SpecifiedValueInfo for u8 {}
+impl SpecifiedValueInfo for u16 {}
+impl SpecifiedValueInfo for u32 {}
+impl SpecifiedValueInfo for str {}
+impl SpecifiedValueInfo for String {}
+
+impl<T: SpecifiedValueInfo + ?Sized> SpecifiedValueInfo for Box<T> {
+    const SUPPORTED_TYPES: u8 = T::SUPPORTED_TYPES;
+}
+
+impl<T: SpecifiedValueInfo> SpecifiedValueInfo for [T] {
+    const SUPPORTED_TYPES: u8 = T::SUPPORTED_TYPES;
+}
+
+macro_rules! impl_generic_specified_value_info {
+    ($ty:ident<$param:ident>) => {
+        impl<$param: SpecifiedValueInfo> SpecifiedValueInfo for $ty<$param> {
+            const SUPPORTED_TYPES: u8 = $param::SUPPORTED_TYPES;
+        }
+    }
+}
+impl_generic_specified_value_info!(Option<T>);
+impl_generic_specified_value_info!(Vec<T>);
+impl_generic_specified_value_info!(Arc<T>);
+impl_generic_specified_value_info!(Range<Idx>);
+
+impl<T1, T2> SpecifiedValueInfo for (T1, T2)
+where
+    T1: SpecifiedValueInfo,
+    T2: SpecifiedValueInfo,
+{
+    const SUPPORTED_TYPES: u8 = T1::SUPPORTED_TYPES | T2::SUPPORTED_TYPES;
+}