diff --git a/Cargo.lock b/Cargo.lock
index c6002808308..6e5c91f372a 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -997,7 +997,6 @@ dependencies = [
  "atomic_refcell 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.23.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "cstr 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)",
- "env_logger 0.5.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.39 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "malloc_size_of 0.0.1",
@@ -3123,6 +3122,7 @@ dependencies = [
  "serde 1.0.37 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo_arc 0.1.1",
  "servo_atoms 0.0.1",
+ "servo_url 0.0.1",
  "webrender_api 0.57.2 (git+https://github.com/servo/webrender)",
 ]
 
diff --git a/components/layout/display_list/builder.rs b/components/layout/display_list/builder.rs
index 141bbb52b80..65b12137c68 100644
--- a/components/layout/display_list/builder.rs
+++ b/components/layout/display_list/builder.rs
@@ -66,9 +66,9 @@ use style::servo::restyle_damage::ServoRestyleDamage;
 use style::values::{Either, RGBA};
 use style::values::computed::Gradient;
 use style::values::computed::effects::SimpleShadow;
-use style::values::computed::pointing::Cursor;
 use style::values::generics::background::BackgroundSize;
 use style::values::generics::image::{GradientKind, Image, PaintWorklet};
+use style::values::generics::pointing::Cursor;
 use style_traits::CSSPixel;
 use style_traits::ToCss;
 use style_traits::cursor::CursorKind;
@@ -2952,11 +2952,11 @@ impl ComputedValuesCursorUtility for ComputedValues {
     fn get_cursor(&self, default_cursor: CursorKind) -> Option<CursorKind> {
         match (
             self.get_pointing().pointer_events,
-            self.get_pointing().cursor,
+            &self.get_pointing().cursor,
         ) {
             (PointerEvents::None, _) => None,
-            (PointerEvents::Auto, Cursor(CursorKind::Auto)) => Some(default_cursor),
-            (PointerEvents::Auto, Cursor(cursor)) => Some(cursor),
+            (PointerEvents::Auto, &Cursor { keyword: CursorKind::Auto, .. }) => Some(default_cursor),
+            (PointerEvents::Auto, &Cursor { keyword, .. }) => Some(keyword),
         }
     }
 }
diff --git a/components/servo_arc/lib.rs b/components/servo_arc/lib.rs
index 04a76c64291..e2063c79a9c 100644
--- a/components/servo_arc/lib.rs
+++ b/components/servo_arc/lib.rs
@@ -39,6 +39,7 @@ use std::convert::From;
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::iter::{ExactSizeIterator, Iterator};
+use std::marker::PhantomData;
 use std::mem;
 use std::ops::{Deref, DerefMut};
 use std::os::raw::c_void;
@@ -924,7 +925,7 @@ impl<T: 'static> Arc<T> {
 ///
 /// ArcBorrow lets us deal with borrows of known-refcounted objects
 /// without needing to worry about how they're actually stored.
-#[derive(Eq, PartialEq)]
+#[derive(Debug, Eq, PartialEq)]
 pub struct ArcBorrow<'a, T: 'a>(&'a T);
 
 impl<'a, T> Copy for ArcBorrow<'a, T> {}
@@ -951,6 +952,10 @@ impl<'a, T> ArcBorrow<'a, T> {
         ArcBorrow(r)
     }
 
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.0 as *const T == other.0 as *const T
+    }
+
     #[inline]
     pub fn with_arc<F, U>(&self, f: F) -> U
     where
@@ -971,6 +976,13 @@ impl<'a, T> ArcBorrow<'a, T> {
         // Forward the result.
         result
     }
+
+    /// Similar to deref, but uses the lifetime |a| rather than the lifetime of
+    /// self, which is incompatible with the signature of the Deref trait.
+    #[inline]
+    pub fn get(&self) -> &'a T {
+        self.0
+    }
 }
 
 impl<'a, T> Deref for ArcBorrow<'a, T> {
@@ -978,7 +990,127 @@ impl<'a, T> Deref for ArcBorrow<'a, T> {
 
     #[inline]
     fn deref(&self) -> &T {
-        &*self.0
+        self.0
+    }
+}
+
+/// A tagged union that can represent Arc<A> or Arc<B> while only consuming a
+/// single word. The type is also NonZero, and thus can be stored in an Option
+/// without increasing size.
+///
+/// This could probably be extended to support four types if necessary.
+pub struct ArcUnion<A: 'static, B: 'static> {
+    p: NonZeroPtrMut<()>,
+    phantom_a: PhantomData<&'static A>,
+    phantom_b: PhantomData<&'static B>,
+}
+
+impl<A: PartialEq + 'static, B: PartialEq + 'static> PartialEq for ArcUnion<A, B> {
+    fn eq(&self, other: &Self) -> bool {
+        use ArcUnionBorrow::*;
+        match (self.borrow(), other.borrow()) {
+            (First(x), First(y)) => x == y,
+            (Second(x), Second(y)) => x == y,
+            (_, _) => false,
+        }
+    }
+}
+
+#[derive(Debug)]
+pub enum ArcUnionBorrow<'a, A: 'static, B: 'static> {
+    First(ArcBorrow<'a, A>),
+    Second(ArcBorrow<'a, B>),
+}
+
+impl<A: 'static, B: 'static> ArcUnion<A, B> {
+    fn new(ptr: *mut ()) -> Self {
+        ArcUnion {
+            p: NonZeroPtrMut::new(ptr),
+            phantom_a: PhantomData,
+            phantom_b: PhantomData,
+        }
+    }
+
+    /// Returns true if the two values are pointer-equal.
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.p == other.p
+    }
+
+    /// Returns an enum representing a borrow of either A or B.
+    pub fn borrow(&self) -> ArcUnionBorrow<A, B> {
+        if self.is_first() {
+            let ptr = self.p.ptr() as *const A;
+            let borrow = unsafe { ArcBorrow::from_ref(&*ptr) };
+            ArcUnionBorrow::First(borrow)
+        } else {
+            let ptr = ((self.p.ptr() as usize) & !0x1) as *const B;
+            let borrow = unsafe { ArcBorrow::from_ref(&*ptr) };
+            ArcUnionBorrow::Second(borrow)
+        }
+    }
+
+    /// Creates an ArcUnion from an instance of the first type.
+    pub fn from_first(other: Arc<A>) -> Self {
+        Self::new(Arc::into_raw(other) as *mut _)
+    }
+
+    /// Creates an ArcUnion from an instance of the second type.
+    pub fn from_second(other: Arc<B>) -> Self {
+        Self::new(((Arc::into_raw(other) as usize) | 0x1) as *mut _)
+    }
+
+    /// Returns true if this ArcUnion contains the first type.
+    pub fn is_first(&self) -> bool {
+        self.p.ptr() as usize & 0x1 == 0
+    }
+
+    /// Returns true if this ArcUnion contains the second type.
+    pub fn is_second(&self) -> bool {
+        !self.is_first()
+    }
+
+    /// Returns a borrow of the first type if applicable, otherwise None.
+    pub fn as_first(&self) -> Option<ArcBorrow<A>> {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => Some(x),
+            ArcUnionBorrow::Second(_) => None,
+        }
+    }
+
+    /// Returns a borrow of the second type if applicable, otherwise None.
+    pub fn as_second(&self) -> Option<ArcBorrow<B>> {
+        match self.borrow() {
+            ArcUnionBorrow::First(_) => None,
+            ArcUnionBorrow::Second(x) => Some(x),
+        }
+    }
+}
+
+impl<A: 'static, B: 'static> Clone for ArcUnion<A, B> {
+    fn clone(&self) -> Self {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => ArcUnion::from_first(x.clone_arc()),
+            ArcUnionBorrow::Second(x) => ArcUnion::from_second(x.clone_arc()),
+        }
+    }
+}
+
+impl<A: 'static, B: 'static> Drop for ArcUnion<A, B> {
+    fn drop(&mut self) {
+        match self.borrow() {
+            ArcUnionBorrow::First(x) => unsafe {
+                let _ = Arc::from_raw(&*x);
+            },
+            ArcUnionBorrow::Second(x) => unsafe {
+                let _ = Arc::from_raw(&*x);
+            },
+        }
+    }
+}
+
+impl<A: fmt::Debug, B: fmt::Debug> fmt::Debug for ArcUnion<A, B> {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        fmt::Debug::fmt(&self.borrow(), f)
     }
 }
 
diff --git a/components/style/applicable_declarations.rs b/components/style/applicable_declarations.rs
index d4674fa1bc7..a1476917fcb 100644
--- a/components/style/applicable_declarations.rs
+++ b/components/style/applicable_declarations.rs
@@ -116,7 +116,7 @@ impl ApplicableDeclarationBlock {
         level: CascadeLevel,
     ) -> Self {
         ApplicableDeclarationBlock {
-            source: StyleSource::Declarations(declarations),
+            source: StyleSource::from_declarations(declarations),
             bits: ApplicableDeclarationBits::new(0, level, 0),
             specificity: 0,
         }
diff --git a/components/style/gecko/data.rs b/components/style/gecko/data.rs
index 331b07ea551..567a9b7f6ca 100644
--- a/components/style/gecko/data.rs
+++ b/components/style/gecko/data.rs
@@ -94,15 +94,15 @@ impl StylesheetInDocument for GeckoStyleSheet {
     }
 
     fn media<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> Option<&'a MediaList> {
-        use gecko_bindings::structs::ServoMediaList;
+        use gecko_bindings::structs::mozilla::dom::MediaList as DomMediaList;
         use std::mem;
 
         unsafe {
-            let servo_media_list = self.raw()._base.mMedia.mRawPtr as *const ServoMediaList;
-            if servo_media_list.is_null() {
+            let dom_media_list = self.raw()._base.mMedia.mRawPtr as *const DomMediaList;
+            if dom_media_list.is_null() {
                 return None;
             }
-            let raw_list = &*(*servo_media_list).mRawList.mRawPtr;
+            let raw_list = &*(*dom_media_list).mRawList.mRawPtr;
             let list = Locked::<MediaList>::as_arc(mem::transmute(&raw_list));
             Some(list.read_with(guard))
         }
diff --git a/components/style/gecko/url.rs b/components/style/gecko/url.rs
index 1b5bc424e4d..bca7e10883a 100644
--- a/components/style/gecko/url.rs
+++ b/components/style/gecko/url.rs
@@ -19,7 +19,7 @@ use style_traits::ParseError;
 
 /// A CSS url() value for gecko.
 #[css(function = "url")]
-#[derive(Clone, Debug, PartialEq, ToCss)]
+#[derive(Clone, Debug, PartialEq, SpecifiedValueInfo, ToCss)]
 pub struct CssUrl {
     /// The URL in unresolved string form.
     ///
@@ -121,7 +121,7 @@ impl MallocSizeOf 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 +179,7 @@ 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..017996f87b5 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)},
@@ -408,9 +408,10 @@
         }
 
         #[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),
+            #[css(skip)]
             System(SystemFont),
         }
 
@@ -558,7 +559,8 @@
         </%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 +571,7 @@
             #[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)}
@@ -617,9 +619,14 @@
     % endif
 </%def>
 
-<%def name="shorthand(name, sub_properties, derive_serialize=False, **kwargs)">
+<%def name="shorthand(name, sub_properties, derive_serialize=False,
+                      derive_value_info=True, **kwargs)">
 <%
     shorthand = data.declare_shorthand(name, sub_properties.split(), **kwargs)
+    # mako doesn't accept non-string value in parameters with <% %> form, so
+    # we have to workaround it this way.
+    if not isinstance(derive_value_info, bool):
+        derive_value_info = eval(derive_value_info)
 %>
     % if shorthand:
     /// ${shorthand.spec}
@@ -634,8 +641,11 @@
         #[allow(unused_imports)]
         use style_traits::{ParseError, StyleParseErrorKind};
         #[allow(unused_imports)]
-        use style_traits::{CssWriter, ToCss};
+        use style_traits::{CssWriter, KeywordsCollectFn, SpecifiedValueInfo, ToCss};
 
+        % if derive_value_info:
+        #[derive(SpecifiedValueInfo)]
+        % endif
         pub struct Longhands {
             % for sub_property in shorthand.sub_properties:
                 pub ${sub_property.ident}:
diff --git a/components/style/properties/helpers/animated_properties.mako.rs b/components/style/properties/helpers/animated_properties.mako.rs
index e2d15139128..57a8ed99880 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::{KeywordsCollectFn, ParseError, SpecifiedValueInfo};
 use super::ComputedValues;
 use values::{CSSFloat, CustomIdent, Either};
 use values::animated::{Animate, Procedure, ToAnimatedValue, ToAnimatedZero};
@@ -172,6 +172,15 @@ impl From<nsCSSPropertyID> for TransitionProperty {
     }
 }
 
+impl SpecifiedValueInfo for TransitionProperty {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        // `transition-property` can actually accept all properties and
+        // arbitrary identifiers, but `all` is a special one we'd like
+        // to list.
+        f(&["all"]);
+    }
+}
+
 /// 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/box.mako.rs b/components/style/properties/longhand/box.mako.rs
index 806afcbd1b6..026a3ca7936 100644
--- a/components/style/properties/longhand/box.mako.rs
+++ b/components/style/properties/longhand/box.mako.rs
@@ -660,9 +660,21 @@ ${helpers.predefined_type(
     products="gecko",
     gecko_pref="layout.css.shape-outside.enabled",
     animation_value_type="ComputedValue",
+    flags="APPLIES_TO_FIRST_LETTER",
     spec="https://drafts.csswg.org/css-shapes/#shape-image-threshold-property",
 )}
 
+${helpers.predefined_type(
+    "shape-margin",
+    "NonNegativeLengthOrPercentage",
+    "computed::NonNegativeLengthOrPercentage::zero()",
+    products="gecko",
+    gecko_pref="layout.css.shape-outside.enabled",
+    animation_value_type="NonNegativeLengthOrPercentage",
+    flags="APPLIES_TO_FIRST_LETTER",
+    spec="https://drafts.csswg.org/css-shapes/#shape-margin-property",
+)}
+
 ${helpers.predefined_type(
     "shape-outside",
     "basic_shape::FloatAreaShape",
diff --git a/components/style/properties/longhand/font.mako.rs b/components/style/properties/longhand/font.mako.rs
index 0477a2cd0d5..7309aca8a38 100644
--- a/components/style/properties/longhand/font.mako.rs
+++ b/components/style/properties/longhand/font.mako.rs
@@ -274,6 +274,11 @@ ${helpers.predefined_type("-x-text-zoom",
         //! detects that a value has a system font, it will resolve it, and
         //! cache it on the ComputedValues. After this, it can be just fetched
         //! whenever a font longhand on the same element needs the system font.
+        //!
+        //! When a longhand property is holding a SystemFont, it's serialized
+        //! to an empty string as if its value comes from a shorthand with
+        //! variable reference. We may want to improve this behavior at some
+        //! point. See also https://github.com/w3c/csswg-drafts/issues/1586.
 
         use app_units::Au;
         use cssparser::{Parser, ToCss};
@@ -296,7 +301,8 @@ ${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)},
@@ -444,7 +450,7 @@ ${helpers.predefined_type("-x-text-zoom",
         // a lot of code with `if product == gecko` conditionals, we have a
         // dummy system font module that does nothing
 
-        #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, ToCss)]
+        #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, SpecifiedValueInfo, ToCss)]
         #[cfg_attr(feature = "servo", derive(MallocSizeOf))]
         /// void enum for system font, can never exist
         pub enum SystemFont {}
diff --git a/components/style/properties/longhand/inherited_text.mako.rs b/components/style/properties/longhand/inherited_text.mako.rs
index abf1054675c..975d7eabe26 100644
--- a/components/style/properties/longhand/inherited_text.mako.rs
+++ b/components/style/properties/longhand/inherited_text.mako.rs
@@ -292,7 +292,6 @@ ${helpers.single_keyword("ruby-position", "over under",
 
 ${helpers.single_keyword("text-combine-upright", "none all",
                          products="gecko", animation_value_type="discrete",
-                         gecko_pref="layout.css.text-combine-upright.enabled",
                          spec="https://drafts.csswg.org/css-writing-modes-3/#text-combine-upright")}
 
 // SVG 1.1: Section 11 - Painting: Filling, Stroking and Marker Symbols
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 1042a5d1a4d..a1d2ee9d085 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, KeywordsCollectFn, 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 +542,43 @@ 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]
+    }
+
+    /// See PropertyId::collect_property_completion_keywords.
+    fn collect_property_completion_keywords(&self, f: KeywordsCollectFn) {
+        const COLLECT_FUNCTIONS: [&Fn(KeywordsCollectFn);
+                                  ${len(data.longhands) + len(data.shorthands)}] = [
+            % for prop in data.longhands:
+                &<${prop.specified_type()} as SpecifiedValueInfo>::collect_completion_keywords,
+            % endfor
+            % for prop in data.shorthands:
+            % if prop.name == "all":
+                &|_f| {}, // 'all' accepts no value other than CSS-wide keywords
+            % else:
+                &<shorthands::${prop.ident}::Longhands as SpecifiedValueInfo>::
+                    collect_completion_keywords,
+            % endif
+            % endfor
+        ];
+        COLLECT_FUNCTIONS[self.0](f);
+    }
 }
 
 impl From<LonghandId> for NonCustomPropertyId {
@@ -724,7 +762,8 @@ impl LonghandIdSet {
 }
 
 /// An enum to represent a CSS Wide keyword.
-#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
 pub enum CSSWideKeyword {
     /// The `initial` keyword.
     Initial,
@@ -1692,6 +1731,18 @@ impl PropertyId {
         })
     }
 
+    /// Returns non-alias NonCustomPropertyId corresponding to this
+    /// property id.
+    fn non_custom_non_alias_id(&self) -> Option<NonCustomPropertyId> {
+        Some(match *self {
+            PropertyId::Custom(_) => return None,
+            PropertyId::Shorthand(id) => id.into(),
+            PropertyId::Longhand(id) => id.into(),
+            PropertyId::ShorthandAlias(id, _) => id.into(),
+            PropertyId::LonghandAlias(id, _) => id.into(),
+        })
+    }
+
     /// Whether the property is enabled for all content regardless of the
     /// stylesheet it was declared on (that is, in practice only checks prefs).
     #[inline]
@@ -1713,6 +1764,24 @@ 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 id = self.non_custom_non_alias_id();
+        id.map_or(0, |id| id.supported_types()) & ty != 0
+    }
+
+    /// Collect supported starting word of values of this property.
+    ///
+    /// See style_traits::SpecifiedValueInfo::collect_completion_keywords for more
+    /// details.
+    pub fn collect_property_completion_keywords(&self, f: KeywordsCollectFn) {
+        if let Some(id) = self.non_custom_non_alias_id() {
+            id.collect_property_completion_keywords(f);
+        }
+        CSSWideKeyword::collect_completion_keywords(f);
+    }
 }
 
 /// A declaration using a CSS-wide keyword.
@@ -3424,7 +3493,7 @@ where
             let source = node.style_source();
 
             let declarations = if source.is_some() {
-                source.read(cascade_level.guard(guards)).declaration_importance_iter()
+                source.as_ref().unwrap().read(cascade_level.guard(guards)).declaration_importance_iter()
             } else {
                 // The root node has no style source.
                 DeclarationImportanceIterator::new(&[], &empty)
diff --git a/components/style/properties/shorthand/border.mako.rs b/components/style/properties/shorthand/border.mako.rs
index 2a675a2c523..056096353bc 100644
--- a/components/style/properties/shorthand/border.mako.rs
+++ b/components/style/properties/shorthand/border.mako.rs
@@ -140,6 +140,7 @@ pub fn parse_border<'i, 't>(
         for prop in ['color', 'style', 'width'])}
         ${' '.join('border-image-%s' % name
         for name in ['outset', 'repeat', 'slice', 'source', 'width'])}"
+    derive_value_info="False"
     spec="https://drafts.csswg.org/css-backgrounds/#border">
 
     pub fn parse_value<'i, 't>(
@@ -202,6 +203,17 @@ pub fn parse_border<'i, 't>(
         }
     }
 
+    // Just use the same as border-left. The border shorthand can't accept
+    // any value that the sub-shorthand couldn't.
+    <%
+        border_left = "<::properties::shorthands::border_left::Longhands as SpecifiedValueInfo>"
+    %>
+    impl SpecifiedValueInfo for Longhands {
+        const SUPPORTED_TYPES: u8 = ${border_left}::SUPPORTED_TYPES;
+        fn collect_completion_keywords(f: KeywordsCollectFn) {
+            ${border_left}::collect_completion_keywords(f);
+        }
+    }
 </%helpers:shorthand>
 
 <%helpers:shorthand name="border-radius" sub_properties="${' '.join(
diff --git a/components/style/properties/shorthand/font.mako.rs b/components/style/properties/shorthand/font.mako.rs
index 5e14fd6ab50..a53f899851c 100644
--- a/components/style/properties/shorthand/font.mako.rs
+++ b/components/style/properties/shorthand/font.mako.rs
@@ -19,6 +19,7 @@
                                     ${'font-language-override' if product == 'gecko' else ''}
                                     ${'font-feature-settings' if product == 'gecko' else ''}
                                     ${'font-variation-settings' if product == 'gecko' else ''}"
+                    derive_value_info="False"
                     spec="https://drafts.csswg.org/css-fonts-3/#propdef-font">
     use parser::Parse;
     use properties::longhands::{font_family, font_style, font_weight, font_stretch};
@@ -258,6 +259,29 @@
         }
         % endif
     }
+
+    <%
+        subprops_for_value_info = ["font_style", "font_weight", "font_stretch",
+                                   "font_variant_caps", "font_size", "font_family"]
+        subprops_for_value_info = [
+            "<longhands::{}::SpecifiedValue as SpecifiedValueInfo>".format(p)
+            for p in subprops_for_value_info
+        ]
+    %>
+    impl SpecifiedValueInfo for Longhands {
+        const SUPPORTED_TYPES: u8 = 0
+            % for p in subprops_for_value_info:
+            | ${p}::SUPPORTED_TYPES
+            % endfor
+            ;
+
+        fn collect_completion_keywords(f: KeywordsCollectFn) {
+            % for p in subprops_for_value_info:
+            ${p}::collect_completion_keywords(f);
+            % endfor
+            <longhands::system_font::SystemFont as SpecifiedValueInfo>::collect_completion_keywords(f);
+        }
+    }
 </%helpers:shorthand>
 
 <%helpers:shorthand name="font-variant"
diff --git a/components/style/properties/shorthand/outline.mako.rs b/components/style/properties/shorthand/outline.mako.rs
index d2f04466629..14b935f3bfd 100644
--- a/components/style/properties/shorthand/outline.mako.rs
+++ b/components/style/properties/shorthand/outline.mako.rs
@@ -5,7 +5,7 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="outline"
-                    sub_properties="outline-width outline-style outline-color"
+                    sub_properties="outline-color outline-style outline-width"
                     derive_serialize="True"
                     spec="https://drafts.csswg.org/css-ui/#propdef-outline">
     use properties::longhands::{outline_color, outline_width, outline_style};
diff --git a/components/style/rule_cache.rs b/components/style/rule_cache.rs
index 9e413659e0e..214b104b5a0 100644
--- a/components/style/rule_cache.rs
+++ b/components/style/rule_cache.rs
@@ -8,7 +8,7 @@
 use fnv::FnvHashMap;
 use logical_geometry::WritingMode;
 use properties::{ComputedValues, StyleBuilder};
-use rule_tree::{StrongRuleNode, StyleSource};
+use rule_tree::StrongRuleNode;
 use selector_parser::PseudoElement;
 use servo_arc::Arc;
 use shared_lock::StylesheetGuards;
@@ -97,16 +97,18 @@ impl RuleCache {
         mut rule_node: Option<&'r StrongRuleNode>,
     ) -> Option<&'r StrongRuleNode> {
         while let Some(node) = rule_node {
-            match *node.style_source() {
-                StyleSource::Declarations(ref decls) => {
-                    let cascade_level = node.cascade_level();
-                    let decls = decls.read_with(cascade_level.guard(guards));
-                    if decls.contains_any_reset() {
-                        break;
-                    }
+            match node.style_source() {
+                Some(s) => match s.as_declarations() {
+                    Some(decls) => {
+                        let cascade_level = node.cascade_level();
+                        let decls = decls.read_with(cascade_level.guard(guards));
+                        if decls.contains_any_reset() {
+                            break;
+                        }
+                    },
+                    None => break,
                 },
-                StyleSource::None => {},
-                StyleSource::Style(_) => break,
+                None => {},
             }
             rule_node = node.parent();
         }
diff --git a/components/style/rule_tree/mod.rs b/components/style/rule_tree/mod.rs
index 1527a743de5..2ce403a666d 100644
--- a/components/style/rule_tree/mod.rs
+++ b/components/style/rule_tree/mod.rs
@@ -12,7 +12,7 @@ use gecko::selector_parser::PseudoElement;
 #[cfg(feature = "gecko")]
 use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use properties::{Importance, LonghandIdSet, PropertyDeclarationBlock};
-use servo_arc::{Arc, ArcBorrow, NonZeroPtrMut};
+use servo_arc::{Arc, ArcBorrow, ArcUnion, ArcUnionBorrow, NonZeroPtrMut};
 use shared_lock::{Locked, SharedRwLockReadGuard, StylesheetGuards};
 use smallvec::SmallVec;
 use std::io::{self, Write};
@@ -89,40 +89,27 @@ impl MallocSizeOf for RuleTree {
 /// more debuggability, and also the ability of show those selectors to
 /// devtools.
 #[derive(Clone, Debug)]
-pub enum StyleSource {
-    /// A style rule stable pointer.
-    Style(Arc<Locked<StyleRule>>),
-    /// A declaration block stable pointer.
-    Declarations(Arc<Locked<PropertyDeclarationBlock>>),
-    /// Indicates no style source. Used to save an Option wrapper around the stylesource in
-    /// RuleNode
-    None,
-}
+pub struct StyleSource(ArcUnion<Locked<StyleRule>, Locked<PropertyDeclarationBlock>>);
 
 impl PartialEq for StyleSource {
     fn eq(&self, other: &Self) -> bool {
-        self.ptr_equals(other)
+        ArcUnion::ptr_eq(&self.0, &other.0)
     }
 }
 
 impl StyleSource {
-    #[inline]
-    fn ptr_equals(&self, other: &Self) -> bool {
-        use self::StyleSource::*;
-        match (self, other) {
-            (&Style(ref one), &Style(ref other)) => Arc::ptr_eq(one, other),
-            (&Declarations(ref one), &Declarations(ref other)) => Arc::ptr_eq(one, other),
-            (&None, _) | (_, &None) => {
-                panic!("Should not check for equality between null StyleSource objects")
-            },
-            _ => false,
-        }
+    /// Creates a StyleSource from a StyleRule.
+    pub fn from_rule(rule: Arc<Locked<StyleRule>>) -> Self {
+        StyleSource(ArcUnion::from_first(rule))
+    }
+
+    /// Creates a StyleSource from a PropertyDeclarationBlock.
+    pub fn from_declarations(decls: Arc<Locked<PropertyDeclarationBlock>>) -> Self {
+        StyleSource(ArcUnion::from_second(decls))
     }
 
     fn dump<W: Write>(&self, guard: &SharedRwLockReadGuard, writer: &mut W) {
-        use self::StyleSource::*;
-
-        if let Style(ref rule) = *self {
+        if let Some(ref rule) = self.0.as_first() {
             let rule = rule.read_with(guard);
             let _ = write!(writer, "{:?}", rule.selectors);
         }
@@ -134,20 +121,31 @@ impl StyleSource {
     /// underlying property declaration block.
     #[inline]
     pub fn read<'a>(&'a self, guard: &'a SharedRwLockReadGuard) -> &'a PropertyDeclarationBlock {
-        let block = match *self {
-            StyleSource::Style(ref rule) => &rule.read_with(guard).block,
-            StyleSource::Declarations(ref block) => block,
-            StyleSource::None => panic!("Cannot call read on StyleSource::None"),
+        let block: &Locked<PropertyDeclarationBlock> = match self.0.borrow() {
+            ArcUnionBorrow::First(ref rule) => &rule.get().read_with(guard).block,
+            ArcUnionBorrow::Second(ref block) => block.get(),
         };
         block.read_with(guard)
     }
 
-    /// Indicates if this StyleSource has a value
-    pub fn is_some(&self) -> bool {
-        match *self {
-            StyleSource::None => false,
-            _ => true,
-        }
+    /// Indicates if this StyleSource is a style rule.
+    pub fn is_rule(&self) -> bool {
+        self.0.is_first()
+    }
+
+    /// Indicates if this StyleSource is a PropertyDeclarationBlock.
+    pub fn is_declarations(&self) -> bool {
+        self.0.is_second()
+    }
+
+    /// Returns the style rule if applicable, otherwise None.
+    pub fn as_rule(&self) -> Option<ArcBorrow<Locked<StyleRule>>> {
+        self.0.as_first()
+    }
+
+    /// Returns the declaration block if applicable, otherwise None.
+    pub fn as_declarations(&self) -> Option<ArcBorrow<Locked<PropertyDeclarationBlock>>> {
+        self.0.as_second()
     }
 }
 
@@ -248,11 +246,12 @@ impl RuleTree {
                             last_cascade_order = shadow_cascade_order;
                             important_inner_shadow.push(SmallVec::new());
                         }
-                        important_inner_shadow.last_mut().unwrap().push(source.clone())
-                    }
-                    SameTreeAuthorNormal => {
-                        important_same_tree.push(source.clone())
+                        important_inner_shadow
+                            .last_mut()
+                            .unwrap()
+                            .push(source.clone())
                     },
+                    SameTreeAuthorNormal => important_same_tree.push(source.clone()),
                     UANormal => important_ua.push(source.clone()),
                     UserNormal => important_user.push(source.clone()),
                     StyleAttributeNormal => {
@@ -391,7 +390,10 @@ impl RuleTree {
         // First walk up until the first less-or-equally specific rule.
         let mut children = SmallVec::<[_; 10]>::new();
         while current.get().level > level {
-            children.push((current.get().source.clone(), current.get().level));
+            children.push((
+                current.get().source.as_ref().unwrap().clone(),
+                current.get().level,
+            ));
             current = current.parent().unwrap().clone();
         }
 
@@ -418,13 +420,14 @@ impl RuleTree {
                 // also equally valid. This is less likely, and would require an
                 // in-place mutation of the source, which is, at best, fiddly,
                 // so let's skip it for now.
-                let is_here_already = match current.get().source {
-                    StyleSource::Declarations(ref already_here) => {
-                        pdb.with_arc(|arc| Arc::ptr_eq(arc, already_here))
-                    },
-                    _ => unreachable!("Replacing non-declarations style?"),
-                };
-
+                let current_decls = current
+                    .get()
+                    .source
+                    .as_ref()
+                    .unwrap()
+                    .as_declarations()
+                    .expect("Replacing non-declarations style?");
+                let is_here_already = ArcBorrow::ptr_eq(&pdb, &current_decls);
                 if is_here_already {
                     debug!("Picking the fast path in rule replacement");
                     return None;
@@ -447,7 +450,7 @@ impl RuleTree {
                 if pdb.read_with(level.guard(guards)).any_important() {
                     current = current.ensure_child(
                         self.root.downgrade(),
-                        StyleSource::Declarations(pdb.clone_arc()),
+                        StyleSource::from_declarations(pdb.clone_arc()),
                         level,
                     );
                 }
@@ -455,7 +458,7 @@ impl RuleTree {
                 if pdb.read_with(level.guard(guards)).any_normal() {
                     current = current.ensure_child(
                         self.root.downgrade(),
-                        StyleSource::Declarations(pdb.clone_arc()),
+                        StyleSource::from_declarations(pdb.clone_arc()),
                         level,
                     );
                 }
@@ -491,7 +494,10 @@ impl RuleTree {
         let mut children = SmallVec::<[_; 10]>::new();
         for node in iter {
             if !node.cascade_level().is_animation() {
-                children.push((node.get().source.clone(), node.cascade_level()));
+                children.push((
+                    node.get().source.as_ref().unwrap().clone(),
+                    node.cascade_level(),
+                ));
             }
             last = node;
         }
@@ -689,7 +695,9 @@ pub struct RuleNode {
 
     /// The actual style source, either coming from a selector in a StyleRule,
     /// or a raw property declaration block (like the style attribute).
-    source: StyleSource,
+    ///
+    /// None for the root node.
+    source: Option<StyleSource>,
 
     /// The cascade level this rule is positioned at.
     level: CascadeLevel,
@@ -775,7 +783,7 @@ impl RuleNode {
         RuleNode {
             root: Some(root),
             parent: Some(parent),
-            source: source,
+            source: Some(source),
             level: level,
             refcount: AtomicUsize::new(1),
             first_child: AtomicPtr::new(ptr::null_mut()),
@@ -789,7 +797,7 @@ impl RuleNode {
         RuleNode {
             root: None,
             parent: None,
-            source: StyleSource::None,
+            source: None,
             level: CascadeLevel::UANormal,
             refcount: AtomicUsize::new(1),
             first_child: AtomicPtr::new(ptr::null_mut()),
@@ -884,7 +892,10 @@ impl RuleNode {
         }
 
         if self.source.is_some() {
-            self.source.dump(self.level.guard(guards), writer);
+            self.source
+                .as_ref()
+                .unwrap()
+                .dump(self.level.guard(guards), writer);
         } else {
             if indent != 0 {
                 warn!("How has this happened?");
@@ -986,7 +997,7 @@ impl StrongRuleNode {
         // WeakRuleNode, and implementing this on WeakRuleNode itself...
         for child in self.get().iter_children() {
             let child_node = unsafe { &*child.ptr() };
-            if child_node.level == level && child_node.source.ptr_equals(&source) {
+            if child_node.level == level && child_node.source.as_ref().unwrap() == &source {
                 return child.upgrade();
             }
             last = Some(child);
@@ -1026,7 +1037,7 @@ impl StrongRuleNode {
                 // we accessed `last`.
                 next = WeakRuleNode::from_ptr(existing);
 
-                if unsafe { &*next.ptr() }.source.ptr_equals(&source) {
+                if unsafe { &*next.ptr() }.source.as_ref().unwrap() == &source {
                     // That node happens to be for the same style source, use
                     // that, and let node fall out of scope.
                     return next.upgrade();
@@ -1054,8 +1065,8 @@ impl StrongRuleNode {
     /// Get the style source corresponding to this rule node. May return `None`
     /// if it's the root node, which means that the node hasn't matched any
     /// rules.
-    pub fn style_source(&self) -> &StyleSource {
-        &self.get().source
+    pub fn style_source(&self) -> Option<&StyleSource> {
+        self.get().source.as_ref()
     }
 
     /// The cascade level for this node
@@ -1317,6 +1328,8 @@ impl StrongRuleNode {
                 let source = node.style_source();
                 let declarations = if source.is_some() {
                     source
+                        .as_ref()
+                        .unwrap()
                         .read(node.cascade_level().guard(guards))
                         .declaration_importance_iter()
                 } else {
@@ -1444,7 +1457,7 @@ impl StrongRuleNode {
             .take_while(|node| node.cascade_level() > CascadeLevel::Animations);
         let mut result = (LonghandIdSet::new(), false);
         for node in iter {
-            let style = node.style_source();
+            let style = node.style_source().unwrap();
             for (decl, important) in style
                 .read(node.cascade_level().guard(guards))
                 .declaration_importance_iter()
@@ -1464,33 +1477,6 @@ impl StrongRuleNode {
         }
         result
     }
-
-    /// Returns PropertyDeclarationBlock for this node.
-    /// This function must be called only for animation level node.
-    fn get_animation_style(&self) -> &Arc<Locked<PropertyDeclarationBlock>> {
-        debug_assert!(
-            self.cascade_level().is_animation(),
-            "The cascade level should be an animation level"
-        );
-        match *self.style_source() {
-            StyleSource::Declarations(ref block) => block,
-            StyleSource::Style(_) => unreachable!("animating style should not be a style rule"),
-            StyleSource::None => unreachable!("animating style should not be none"),
-        }
-    }
-
-    /// Returns SMIL override declaration block if exists.
-    pub fn get_smil_animation_rule(&self) -> Option<&Arc<Locked<PropertyDeclarationBlock>>> {
-        if cfg!(feature = "servo") {
-            // Servo has no knowledge of a SMIL rule, so just avoid looking for it.
-            return None;
-        }
-
-        self.self_and_ancestors()
-            .take_while(|node| node.cascade_level() >= CascadeLevel::SMILOverride)
-            .find(|node| node.cascade_level() == CascadeLevel::SMILOverride)
-            .map(|node| node.get_animation_style())
-    }
 }
 
 /// An iterator over a rule node and its ancestors.
diff --git a/components/style/servo/url.rs b/components/style/servo/url.rs
index b5eba690d36..c0867122ae3 100644
--- a/components/style/servo/url.rs
+++ b/components/style/servo/url.rs
@@ -23,7 +23,7 @@ use values::computed::{Context, ToComputedValue};
 ///
 /// However, this approach is still not necessarily optimal: See
 /// <https://bugzilla.mozilla.org/show_bug.cgi?id=1347435#c6>
-#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize)]
+#[derive(Clone, Debug, Deserialize, MallocSizeOf, Serialize, SpecifiedValueInfo)]
 pub struct CssUrl {
     /// The original URI. This might be optional since we may insert computed
     /// values of images into the cascade directly, and we don't bother to
diff --git a/components/style/stylist.rs b/components/style/stylist.rs
index ccd668b0bed..a76a461b73f 100644
--- a/components/style/stylist.rs
+++ b/components/style/stylist.rs
@@ -1523,7 +1523,7 @@ impl Stylist {
         // just avoid allocating it and calling `apply_declarations` directly,
         // maybe...
         let rule_node = self.rule_tree.insert_ordered_rules(iter::once((
-            StyleSource::Declarations(declarations),
+            StyleSource::from_declarations(declarations),
             CascadeLevel::StyleAttributeNormal,
         )));
 
@@ -2177,7 +2177,7 @@ impl CascadeData {
                                     .expect("Expected precomputed declarations for the UA level")
                                     .get_or_insert_with(&pseudo.canonical(), Vec::new)
                                     .push(ApplicableDeclarationBlock::new(
-                                        StyleSource::Style(locked.clone()),
+                                        StyleSource::from_rule(locked.clone()),
                                         self.rules_source_order,
                                         CascadeLevel::UANormal,
                                         selector.specificity(),
@@ -2480,7 +2480,7 @@ impl Rule {
         level: CascadeLevel,
         shadow_cascade_order: ShadowCascadeOrder,
     ) -> ApplicableDeclarationBlock {
-        let source = StyleSource::Style(self.style_rule.clone());
+        let source = StyleSource::from_rule(self.style_rule.clone());
         ApplicableDeclarationBlock::new(source, self.source_order, level, self.specificity(), shadow_cascade_order)
     }
 
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/computed/percentage.rs b/components/style/values/computed/percentage.rs
index 7ca504d2aff..653532aea6c 100644
--- a/components/style/values/computed/percentage.rs
+++ b/components/style/values/computed/percentage.rs
@@ -12,8 +12,9 @@ use values::generics::NonNegative;
 
 /// A computed percentage.
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, Default, MallocSizeOf, PartialEq,
-         PartialOrd, ToAnimatedZero, ToComputedValue)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, Default,
+         MallocSizeOf, PartialEq, PartialOrd, SpecifiedValueInfo,
+         ToAnimatedZero, ToComputedValue)]
 pub struct Percentage(pub CSSFloat);
 
 impl Percentage {
diff --git a/components/style/values/computed/pointing.rs b/components/style/values/computed/pointing.rs
index a0102c12070..a89db9104c3 100644
--- a/components/style/values/computed/pointing.rs
+++ b/components/style/values/computed/pointing.rs
@@ -6,137 +6,16 @@
 //!
 //! https://drafts.csswg.org/css-ui/#pointing-keyboard
 
-use cssparser::Parser;
-use parser::{Parse, ParserContext};
-use selectors::parser::SelectorParseErrorKind;
-#[cfg(feature = "gecko")]
-use std::fmt::{self, Write};
-#[cfg(feature = "gecko")]
-use style_traits::{CssWriter, ToCss};
-use style_traits::ParseError;
-use style_traits::cursor::CursorKind;
+use values::computed::Number;
 use values::computed::color::Color;
-use values::generics::pointing::CaretColor as GenericCaretColor;
-#[cfg(feature = "gecko")]
-use values::specified::url::SpecifiedImageUrl;
-
-/// The computed value for the `cursor` property.
-///
-/// https://drafts.csswg.org/css-ui/#cursor
-pub use values::specified::pointing::Cursor;
-#[cfg(feature = "gecko")]
-pub use values::specified::pointing::CursorImage;
-
-impl Cursor {
-    /// Set `cursor` to `auto`
-    #[cfg(feature = "servo")]
-    #[inline]
-    pub fn auto() -> Self {
-        Cursor(CursorKind::Auto)
-    }
-
-    /// Set `cursor` to `auto`
-    #[cfg(feature = "gecko")]
-    #[inline]
-    pub fn auto() -> Self {
-        Self {
-            images: vec![].into_boxed_slice(),
-            keyword: CursorKind::Auto,
-        }
-    }
-}
-
-impl Parse for Cursor {
-    /// cursor: [auto | default | ...]
-    #[cfg(feature = "servo")]
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Ok(Cursor(CursorKind::parse(context, input)?))
-    }
-
-    /// cursor: [<url> [<number> <number>]?]# [auto | default | ...]
-    #[cfg(feature = "gecko")]
-    fn parse<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        let mut images = vec![];
-        loop {
-            match input.try(|input| CursorImage::parse_image(context, input)) {
-                Ok(image) => images.push(image),
-                Err(_) => break,
-            }
-            input.expect_comma()?;
-        }
-        Ok(Self {
-            images: images.into_boxed_slice(),
-            keyword: CursorKind::parse(context, input)?,
-        })
-    }
-}
-
-#[cfg(feature = "gecko")]
-impl ToCss for Cursor {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        for url in &*self.images {
-            url.to_css(dest)?;
-            dest.write_str(", ")?;
-        }
-        self.keyword.to_css(dest)
-    }
-}
-
-impl Parse for CursorKind {
-    fn parse<'i, 't>(
-        _context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        let location = input.current_source_location();
-        let ident = input.expect_ident()?;
-        CursorKind::from_css_keyword(&ident).map_err(|_| {
-            location.new_custom_error(SelectorParseErrorKind::UnexpectedIdent(ident.clone()))
-        })
-    }
-}
-
-#[cfg(feature = "gecko")]
-impl CursorImage {
-    fn parse_image<'i, 't>(
-        context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<Self, ParseError<'i>> {
-        Ok(Self {
-            url: SpecifiedImageUrl::parse(context, input)?,
-            // FIXME(emilio): Should use Number::parse to handle calc() correctly.
-            hotspot: match input.try(|input| input.expect_number()) {
-                Ok(number) => Some((number, input.expect_number()?)),
-                Err(_) => None,
-            },
-        })
-    }
-}
-
-#[cfg(feature = "gecko")]
-impl ToCss for CursorImage {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        self.url.to_css(dest)?;
-        if let Some((x, y)) = self.hotspot {
-            dest.write_str(" ")?;
-            x.to_css(dest)?;
-            dest.write_str(" ")?;
-            y.to_css(dest)?;
-        }
-        Ok(())
-    }
-}
+use values::computed::url::ComputedImageUrl;
+use values::generics::pointing as generics;
 
 /// A computed value for the `caret-color` property.
-pub type CaretColor = GenericCaretColor<Color>;
+pub type CaretColor = generics::CaretColor<Color>;
+
+/// A computed value for the `cursor` property.
+pub type Cursor = generics::Cursor<CursorImage>;
+
+/// A computed value for item of `image cursors`.
+pub type CursorImage = generics::CursorImage<ComputedImageUrl, Number>;
diff --git a/components/style/values/computed/text.rs b/components/style/values/computed/text.rs
index 7afb774effc..f2bcf11fe62 100644
--- a/components/style/values/computed/text.rs
+++ b/components/style/values/computed/text.rs
@@ -15,8 +15,7 @@ use values::generics::text::InitialLetter as GenericInitialLetter;
 use values::generics::text::LineHeight as GenericLineHeight;
 use values::generics::text::MozTabSize as GenericMozTabSize;
 use values::generics::text::Spacing;
-use values::specified::text::{TextDecorationLine, TextEmphasisFillMode};
-use values::specified::text::{TextEmphasisShapeKeyword, TextOverflowSide};
+use values::specified::text::{TextEmphasisFillMode, TextEmphasisShapeKeyword, TextOverflowSide};
 
 pub use values::specified::TextAlignKeyword as TextAlign;
 pub use values::specified::TextEmphasisPosition;
@@ -79,36 +78,6 @@ impl ToCss for TextOverflow {
     }
 }
 
-impl ToCss for TextDecorationLine {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        let mut has_any = false;
-
-        macro_rules! write_value {
-            ($line:path => $css:expr) => {
-                if self.contains($line) {
-                    if has_any {
-                        dest.write_str(" ")?;
-                    }
-                    dest.write_str($css)?;
-                    has_any = true;
-                }
-            };
-        }
-        write_value!(TextDecorationLine::UNDERLINE => "underline");
-        write_value!(TextDecorationLine::OVERLINE => "overline");
-        write_value!(TextDecorationLine::LINE_THROUGH => "line-through");
-        write_value!(TextDecorationLine::BLINK => "blink");
-        if !has_any {
-            dest.write_str("none")?;
-        }
-
-        Ok(())
-    }
-}
-
 /// A struct that represents the _used_ value of the text-decoration property.
 ///
 /// FIXME(emilio): This is done at style resolution time, though probably should
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..3bad738c1e6 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 +69,9 @@ 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)]
+#[css(function = "inset")]
+#[derive(Animate, Clone, ComputeSquaredDistance, Debug, MallocSizeOf, PartialEq,
+         SpecifiedValueInfo, ToComputedValue)]
 pub struct InsetRect<LengthOrPercentage> {
     pub rect: Rect<LengthOrPercentage>,
     pub round: Option<BorderRadius<LengthOrPercentage>>,
@@ -74,8 +79,9 @@ pub struct InsetRect<LengthOrPercentage> {
 
 /// <https://drafts.csswg.org/css-shapes/#funcdef-circle>
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToComputedValue)]
+#[css(function)]
+#[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 +89,9 @@ 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)]
+#[css(function)]
+#[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 +100,8 @@ 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 +113,9 @@ 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)]
+#[css(function)]
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
 pub struct Polygon<LengthOrPercentage> {
     /// The filling rule for a polygon.
     pub fill: FillRule,
@@ -120,7 +129,8 @@ 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..6230a1cf36a 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),
@@ -21,17 +22,19 @@ 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>,
     /// Whether to fill the middle part.
+    #[value_info(represents_keyword)]
     pub fill: bool,
 }
 
 /// 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 +45,9 @@ 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 +60,8 @@ 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..7373cd8e947 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> {
@@ -55,8 +57,9 @@ 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)]
-pub struct Counters<I>(Box<[(CustomIdent, I)]>);
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
+pub struct Counters<I>(#[css(if_empty = "none")] Box<[(CustomIdent, I)]>);
 
 impl<I> Default for Counters<I> {
     #[inline]
diff --git a/components/style/values/generics/effects.rs b/components/style/values/generics/effects.rs
index e306699eeb2..7a76cdeb7bc 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>,
@@ -18,13 +19,14 @@ pub struct BoxShadow<Color, SizeLength, BlurShapeLength, ShapeLength> {
     pub spread: ShapeLength,
     /// Whether this is an inset box shadow.
     #[animation(constant)]
+    #[value_info(represents_keyword)]
     pub inset: bool,
 }
 
 /// 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 +68,8 @@ 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..f5e62e0ab5f 100644
--- a/components/style/values/generics/font.rs
+++ b/components/style/values/generics/font.rs
@@ -11,11 +11,13 @@ 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, KeywordsCollectFn, ParseError};
+use style_traits::{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 +47,8 @@ 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 +72,8 @@ 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 +109,8 @@ 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 {
@@ -177,20 +182,30 @@ where
     }
 }
 
+impl<L> SpecifiedValueInfo for KeywordInfo<L> {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        <KeywordSize as SpecifiedValueInfo>::collect_completion_keywords(f);
+    }
+}
+
 /// CSS font keywords
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf, PartialEq,
-         ToAnimatedValue, ToAnimatedZero)]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         Parse, PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero,
+         ToCss)]
 #[allow(missing_docs)]
 pub enum KeywordSize {
+    #[css(keyword = "xx-small")]
     XXSmall,
     XSmall,
     Small,
     Medium,
     Large,
     XLarge,
+    #[css(keyword = "xx-large")]
     XXLarge,
     // This is not a real font keyword and will not parse
     // HTML font-size 7 corresponds to this value
+    #[css(skip)]
     XXXLarge,
 }
 
@@ -208,41 +223,18 @@ impl Default for KeywordSize {
     }
 }
 
-impl ToCss for KeywordSize {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        dest.write_str(match *self {
-            KeywordSize::XXSmall => "xx-small",
-            KeywordSize::XSmall => "x-small",
-            KeywordSize::Small => "small",
-            KeywordSize::Medium => "medium",
-            KeywordSize::Large => "large",
-            KeywordSize::XLarge => "x-large",
-            KeywordSize::XXLarge => "xx-large",
-            KeywordSize::XXXLarge => {
-                debug_assert!(
-                    false,
-                    "We should never serialize specified values set via HTML presentation attributes"
-                );
-                "-servo-xxx-large"
-            },
-        })
-    }
-}
-
 /// A generic value for the `font-style` property.
 ///
 /// https://drafts.csswg.org/css-fonts-4/#font-style-prop
 #[allow(missing_docs)]
-#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
-         PartialEq, ToAnimatedValue, ToAnimatedZero)]
 #[cfg_attr(feature = "servo", derive(Deserialize, Serialize))]
+#[derive(Animate, Clone, ComputeSquaredDistance, Copy, Debug, MallocSizeOf,
+         PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToAnimatedZero)]
 pub enum FontStyle<Angle> {
     #[animation(error)]
     Normal,
     #[animation(error)]
     Italic,
+    #[value_info(starts_with_keyword)]
     Oblique(Angle),
 }
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..b9ec85ace22 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>),
@@ -195,10 +198,12 @@ pub enum TrackSize<L> {
     /// and a flexible `<track-breadth>`
     ///
     /// <https://drafts.csswg.org/css-grid/#valdef-grid-template-columns-minmax>
+    #[css(function)]
     Minmax(TrackBreadth<L>, TrackBreadth<L>),
     /// A `fit-content` function.
     ///
     /// <https://drafts.csswg.org/css-grid/#valdef-grid-template-columns-fit-content>
+    #[css(function)]
     FitContent(L),
 }
 
@@ -378,7 +383,9 @@ 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)]
+#[css(function = "repeat")]
 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 +471,8 @@ 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>),
@@ -497,12 +505,13 @@ 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).
     ///
     /// In order to avoid parsing the same value multiple times, this does a single traversal
     /// and arrives at the type of value it has parsed (or bails out gracefully with an error).
+    #[css(skip)]
     pub list_type: TrackListType,
     /// A vector of `<track-size> | <track-repeat>` values.
     pub values: Vec<TrackListValue<LengthOrPercentage, Integer>>,
@@ -569,7 +578,8 @@ 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 +682,8 @@ 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..2da4d290039 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),
@@ -26,6 +26,7 @@ pub enum Image<Gradient, MozImageRect, ImageUrl> {
     /// A `-moz-image-rect` image.  Also fairly large and rare.
     Rect(Box<MozImageRect>),
     /// A `-moz-element(# <element-id>)`
+    #[css(function = "-moz-element")]
     Element(Atom),
     /// A paint worklet image.
     /// <https://drafts.css-houdini.org/css-paint-api/>
@@ -144,6 +145,8 @@ pub struct PaintWorklet {
     pub arguments: Vec<Arc<custom_properties::SpecifiedValue>>,
 }
 
+impl ::style_traits::SpecifiedValueInfo for PaintWorklet { }
+
 impl ToCss for PaintWorklet {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
     where
@@ -164,7 +167,8 @@ 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..59d9748ea5b 100644
--- a/components/style/values/generics/mod.rs
+++ b/components/style/values/generics/mod.rs
@@ -8,7 +8,8 @@
 use counter_style::{parse_counter_style_name, Symbols};
 use cssparser::Parser;
 use parser::{Parse, ParserContext};
-use style_traits::{ParseError, StyleParseErrorKind};
+use style_traits::{KeywordsCollectFn, ParseError};
+use style_traits::{SpecifiedValueInfo, StyleParseErrorKind};
 use super::CustomIdent;
 
 pub mod background;
@@ -137,14 +138,32 @@ impl Parse for CounterStyleOrNone {
     }
 }
 
+impl SpecifiedValueInfo for CounterStyleOrNone {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        // XXX The best approach for implementing this is probably
+        // having a CounterStyleName type wrapping CustomIdent, and
+        // put the predefined list for that type in counter_style mod.
+        // But that's a non-trivial change itself, so we use a simpler
+        // approach here.
+        macro_rules! predefined {
+            ($($name:expr,)+) => {
+                f(&["none", "symbols", $($name,)+]);
+            }
+        }
+        include!("../../counter_style/predefined.rs");
+    }
+}
+
 /// 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 7e55c4a5a75..9d9ec031225 100644
--- a/components/style/values/generics/pointing.rs
+++ b/components/style/values/generics/pointing.rs
@@ -4,12 +4,79 @@
 
 //! Generic values for pointing properties.
 
+use std::fmt::{self, Write};
+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),
     /// The keyword `auto`.
     Auto,
 }
+
+/// A generic value for the `cursor` property.
+///
+/// https://drafts.csswg.org/css-ui/#cursor
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
+pub struct Cursor<Image> {
+    /// The parsed images for the cursor.
+    pub images: Box<[Image]>,
+    /// The kind of the cursor [default | help | ...].
+    pub keyword: CursorKind,
+}
+
+impl<Image> Cursor<Image> {
+    /// Set `cursor` to `auto`
+    #[inline]
+    pub fn auto() -> Self {
+        Self {
+            images: vec![].into_boxed_slice(),
+            keyword: CursorKind::Auto,
+        }
+    }
+}
+
+impl<Image: ToCss> ToCss for Cursor<Image> {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        for image in &*self.images {
+            image.to_css(dest)?;
+            dest.write_str(", ")?;
+        }
+        self.keyword.to_css(dest)
+    }
+}
+
+/// A generic value for item of `image cursors`.
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
+pub struct CursorImage<ImageUrl, Number> {
+    /// The url to parse images from.
+    pub url: ImageUrl,
+    /// The <x> and <y> coordinates.
+    pub hotspot: Option<(Number, Number)>,
+}
+
+impl<ImageUrl: ToCss, Number: ToCss> ToCss for CursorImage<ImageUrl, Number> {
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        self.url.to_css(dest)?;
+        if let Some((ref x, ref y)) = self.hotspot {
+            dest.write_str(" ")?;
+            x.to_css(dest)?;
+            dest.write_str(" ")?;
+            y.to_css(dest)?;
+        }
+        Ok(())
+    }
+}
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..ecd40f5a55c 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,
@@ -78,7 +80,9 @@ pub struct TransformOrigin<H, V, Depth> {
 /// A generic timing function.
 ///
 /// <https://drafts.csswg.org/css-timing-1/#single-timing-function-production>
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToCss)]
+#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToCss)]
+#[value_info(ty = "TIMING_FUNCTION")]
 pub enum TimingFunction<Integer, Number> {
     /// `linear | ease | ease-in | ease-out | ease-in-out`
     Keyword(TimingKeyword),
@@ -93,6 +97,7 @@ pub enum TimingFunction<Integer, Number> {
     },
     /// `step-start | step-end | steps(<integer>, [ start | end ]?)`
     #[css(comma, function)]
+    #[value_info(other_values = "step-start,step-end")]
     Steps(Integer, #[css(skip_if = "is_end")] StepPosition),
     /// `frames(<integer>)`
     #[css(comma, function)]
@@ -101,7 +106,8 @@ pub enum TimingFunction<Integer, Number> {
 
 #[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 TimingKeyword {
     Linear,
     Ease,
@@ -157,7 +163,8 @@ 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 +268,8 @@ 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 +562,8 @@ 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 +576,8 @@ 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 +592,8 @@ 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 +609,8 @@ 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..f02242e78d1 100644
--- a/components/style/values/mod.rs
+++ b/components/style/values/mod.rs
@@ -71,7 +71,7 @@ where
 
 /// Convenience void type to disable some properties and values through types.
 #[cfg_attr(feature = "servo", derive(Deserialize, MallocSizeOf, Serialize))]
-#[derive(Clone, Copy, Debug, PartialEq, ToAnimatedValue, ToComputedValue, ToCss)]
+#[derive(Clone, Copy, Debug, PartialEq, SpecifiedValueInfo, ToAnimatedValue, ToComputedValue, ToCss)]
 pub enum Impossible {}
 
 // FIXME(nox): This should be derived but the derive code cannot cope
@@ -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, SpecifiedValueInfo, ToComputedValue)]
 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..731844bcb52 100644
--- a/components/style/values/specified/align.rs
+++ b/components/style/values/specified/align.rs
@@ -10,7 +10,7 @@ use cssparser::Parser;
 use gecko_bindings::structs;
 use parser::{Parse, ParserContext};
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, ToCss};
+use style_traits::{CssWriter, KeywordsCollectFn, ParseError, SpecifiedValueInfo, ToCss};
 
 bitflags! {
     /// Constants shared by multiple CSS Box Alignment properties
@@ -191,6 +191,9 @@ impl ContentDistribution {
         input: &mut Parser<'i, 't>,
         axis: AxisDirection,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update the `list_keywords` function below
+        //      when this function is updated.
+
         // Try to parse normal first
         if input.try(|i| i.expect_ident_matching("normal")).is_ok() {
             return Ok(ContentDistribution::normal());
@@ -227,6 +230,19 @@ impl ContentDistribution {
             content_position | overflow_position,
         ))
     }
+
+    fn list_keywords(f: KeywordsCollectFn, axis: AxisDirection) {
+        f(&["normal"]);
+        if axis == AxisDirection::Block {
+            list_baseline_keywords(f);
+        }
+        list_content_distribution_keywords(f);
+        list_overflow_position_keywords(f);
+        f(&["start", "end", "flex-start", "flex-end", "center"]);
+        if axis == AxisDirection::Inline {
+            f(&["left", "right"]);
+        }
+    }
 }
 
 /// Value for the `align-content` property.
@@ -240,6 +256,8 @@ impl Parse for AlignContent {
         _: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update `impl SpecifiedValueInfo` below when
+        //      this function is updated.
         Ok(AlignContent(ContentDistribution::parse(
             input,
             AxisDirection::Block,
@@ -247,6 +265,12 @@ impl Parse for AlignContent {
     }
 }
 
+impl SpecifiedValueInfo for AlignContent {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        ContentDistribution::list_keywords(f, AxisDirection::Block);
+    }
+}
+
 #[cfg(feature = "gecko")]
 impl From<u16> for AlignContent {
     fn from(bits: u16) -> Self {
@@ -272,6 +296,8 @@ impl Parse for JustifyContent {
         _: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update `impl SpecifiedValueInfo` below when
+        //      this function is updated.
         Ok(JustifyContent(ContentDistribution::parse(
             input,
             AxisDirection::Inline,
@@ -279,6 +305,12 @@ impl Parse for JustifyContent {
     }
 }
 
+impl SpecifiedValueInfo for JustifyContent {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        ContentDistribution::list_keywords(f, AxisDirection::Inline);
+    }
+}
+
 #[cfg(feature = "gecko")]
 impl From<u16> for JustifyContent {
     fn from(bits: u16) -> Self {
@@ -319,6 +351,9 @@ impl SelfAlignment {
         input: &mut Parser<'i, 't>,
         axis: AxisDirection,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update the `list_keywords` function below
+        //      when this function is updated.
+
         // <baseline-position>
         //
         // It's weird that this accepts <baseline-position>, but not
@@ -339,6 +374,13 @@ impl SelfAlignment {
         let self_position = parse_self_position(input, axis)?;
         Ok(SelfAlignment(overflow_position | self_position))
     }
+
+    fn list_keywords(f: KeywordsCollectFn, axis: AxisDirection) {
+        list_baseline_keywords(f);
+        list_auto_normal_stretch(f);
+        list_overflow_position_keywords(f);
+        list_self_position_keywords(f, axis);
+    }
 }
 
 /// The specified value of the align-self property.
@@ -352,6 +394,8 @@ impl Parse for AlignSelf {
         _: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update `impl SpecifiedValueInfo` below when
+        //      this function is updated.
         Ok(AlignSelf(SelfAlignment::parse(
             input,
             AxisDirection::Block,
@@ -359,6 +403,12 @@ impl Parse for AlignSelf {
     }
 }
 
+impl SpecifiedValueInfo for AlignSelf {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        SelfAlignment::list_keywords(f, AxisDirection::Block);
+    }
+}
+
 impl From<u8> for AlignSelf {
     fn from(bits: u8) -> Self {
         AlignSelf(SelfAlignment(AlignFlags::from_bits_truncate(bits)))
@@ -382,6 +432,8 @@ impl Parse for JustifySelf {
         _: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update `impl SpecifiedValueInfo` below when
+        //      this function is updated.
         Ok(JustifySelf(SelfAlignment::parse(
             input,
             AxisDirection::Inline,
@@ -389,6 +441,12 @@ impl Parse for JustifySelf {
     }
 }
 
+impl SpecifiedValueInfo for JustifySelf {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        SelfAlignment::list_keywords(f, AxisDirection::Inline);
+    }
+}
+
 impl From<u8> for JustifySelf {
     fn from(bits: u8) -> Self {
         JustifySelf(SelfAlignment(AlignFlags::from_bits_truncate(bits)))
@@ -422,6 +480,9 @@ impl Parse for AlignItems {
         _: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update `impl SpecifiedValueInfo` below when
+        //      this function is updated.
+
         // <baseline-position>
         if let Ok(baseline) = input.try(parse_baseline) {
             return Ok(AlignItems(baseline));
@@ -440,6 +501,15 @@ impl Parse for AlignItems {
     }
 }
 
+impl SpecifiedValueInfo for AlignItems {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        list_baseline_keywords(f);
+        list_normal_stretch(f);
+        list_overflow_position_keywords(f);
+        list_self_position_keywords(f, AxisDirection::Block);
+    }
+}
+
 /// Value of the `justify-items` property
 ///
 /// <https://drafts.csswg.org/css-align/#justify-items-property>
@@ -465,6 +535,9 @@ impl Parse for JustifyItems {
         _: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
+        // NOTE Please also update `impl SpecifiedValueInfo` below when
+        //      this function is updated.
+
         // <baseline-position>
         //
         // It's weird that this accepts <baseline-position>, but not
@@ -492,10 +565,22 @@ impl Parse for JustifyItems {
     }
 }
 
+impl SpecifiedValueInfo for JustifyItems {
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        list_baseline_keywords(f);
+        list_normal_stretch(f);
+        list_legacy_keywords(f);
+        list_overflow_position_keywords(f);
+        list_self_position_keywords(f, AxisDirection::Inline);
+    }
+}
+
 // auto | normal | stretch
 fn parse_auto_normal_stretch<'i, 't>(
     input: &mut Parser<'i, 't>,
 ) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_auto_normal_stretch` function
+    //      below when this function is updated.
     try_match_ident_ignore_ascii_case! { input,
         "auto" => Ok(AlignFlags::AUTO),
         "normal" => Ok(AlignFlags::NORMAL),
@@ -503,16 +588,28 @@ fn parse_auto_normal_stretch<'i, 't>(
     }
 }
 
+fn list_auto_normal_stretch(f: KeywordsCollectFn) {
+    f(&["auto", "normal", "stretch"]);
+}
+
 // normal | stretch
 fn parse_normal_stretch<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_normal_stretch` function below
+    //      when this function is updated.
     try_match_ident_ignore_ascii_case! { input,
         "normal" => Ok(AlignFlags::NORMAL),
         "stretch" => Ok(AlignFlags::STRETCH),
     }
 }
 
+fn list_normal_stretch(f: KeywordsCollectFn) {
+    f(&["normal", "stretch"]);
+}
+
 // <baseline-position>
 fn parse_baseline<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_baseline_keywords` function
+    //      below when this function is updated.
     try_match_ident_ignore_ascii_case! { input,
         "baseline" => Ok(AlignFlags::BASELINE),
         "first" => {
@@ -526,10 +623,16 @@ fn parse_baseline<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, Pars
     }
 }
 
+fn list_baseline_keywords(f: KeywordsCollectFn) {
+    f(&["baseline", "first baseline", "last baseline"]);
+}
+
 // <content-distribution>
 fn parse_content_distribution<'i, 't>(
     input: &mut Parser<'i, 't>,
 ) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_content_distribution_keywords`
+    //      function below when this function is updated.
     try_match_ident_ignore_ascii_case! { input,
         "stretch" => Ok(AlignFlags::STRETCH),
         "space-between" => Ok(AlignFlags::SPACE_BETWEEN),
@@ -538,21 +641,33 @@ fn parse_content_distribution<'i, 't>(
     }
 }
 
+fn list_content_distribution_keywords(f: KeywordsCollectFn) {
+    f(&["stretch", "space-between", "space-around", "space-evenly"]);
+}
+
 // <overflow-position>
 fn parse_overflow_position<'i, 't>(
     input: &mut Parser<'i, 't>,
 ) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_overflow_position_keywords`
+    //      function below when this function is updated.
     try_match_ident_ignore_ascii_case! { input,
         "safe" => Ok(AlignFlags::SAFE),
         "unsafe" => Ok(AlignFlags::UNSAFE),
     }
 }
 
+fn list_overflow_position_keywords(f: KeywordsCollectFn) {
+    f(&["safe", "unsafe"]);
+}
+
 // <self-position> | left | right in the inline axis.
 fn parse_self_position<'i, 't>(
     input: &mut Parser<'i, 't>,
     axis: AxisDirection,
 ) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_self_position_keywords`
+    //      function below when this function is updated.
     Ok(try_match_ident_ignore_ascii_case! { input,
         "start" => AlignFlags::START,
         "end" => AlignFlags::END,
@@ -566,9 +681,21 @@ fn parse_self_position<'i, 't>(
     })
 }
 
+fn list_self_position_keywords(f: KeywordsCollectFn, axis: AxisDirection) {
+    f(&[
+      "start", "end", "flex-start", "flex-end",
+      "center", "self-start", "self-end",
+    ]);
+    if axis == AxisDirection::Inline {
+        f(&["left", "right"]);
+    }
+}
+
 fn parse_left_right_center<'i, 't>(
     input: &mut Parser<'i, 't>,
 ) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_legacy_keywords` function below
+    //      when this function is updated.
     Ok(try_match_ident_ignore_ascii_case! { input,
         "left" => AlignFlags::LEFT,
         "right" => AlignFlags::RIGHT,
@@ -578,6 +705,8 @@ fn parse_left_right_center<'i, 't>(
 
 // legacy | [ legacy && [ left | right | center ] ]
 fn parse_legacy<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseError<'i>> {
+    // NOTE Please also update the `list_legacy_keywords` function below
+    //      when this function is updated.
     let flags = try_match_ident_ignore_ascii_case! { input,
         "legacy" => {
             let flags = input.try(parse_left_right_center)
@@ -593,3 +722,7 @@ fn parse_legacy<'i, 't>(input: &mut Parser<'i, 't>) -> Result<AlignFlags, ParseE
     input.expect_ident_matching("legacy")?;
     Ok(AlignFlags::LEGACY | flags)
 }
+
+fn list_legacy_keywords(f: KeywordsCollectFn) {
+    f(&["legacy", "left", "right", "center"]);
+}
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..f56d6afd430 100644
--- a/components/style/values/specified/box.rs
+++ b/components/style/values/specified/box.rs
@@ -10,8 +10,7 @@ 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 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 +296,9 @@ 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)]
+#[value_info(other_values = "none")]
 pub struct AnimationName(pub Option<KeyframesName>);
 
 impl AnimationName {
@@ -339,7 +341,8 @@ 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 +351,8 @@ 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 +361,15 @@ 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
@@ -415,8 +421,9 @@ impl Parse for WillChange {
 
 bitflags! {
     #[cfg_attr(feature = "gecko", derive(MallocSizeOf))]
-    #[derive(ToComputedValue)]
+    #[derive(SpecifiedValueInfo, ToComputedValue)]
     /// These constants match Gecko's `NS_STYLE_TOUCH_ACTION_*` constants.
+    #[value_info(other_values = "auto,none,manipulation,pan-x,pan-y")]
     pub struct TouchAction: u8 {
         /// `none` variant
         const TOUCH_ACTION_NONE = 1 << 0;
@@ -515,7 +522,8 @@ pub fn assert_touch_action_matches() {
 }
 
 bitflags! {
-    #[derive(MallocSizeOf, ToComputedValue)]
+    #[derive(MallocSizeOf, SpecifiedValueInfo, ToComputedValue)]
+    #[value_info(other_values = "none,strict,layout,style,paint")]
     /// Constants for contain: https://drafts.csswg.org/css-contain/#contain-property
     pub struct Contain: u8 {
         /// `layout` variant, turns on layout containment
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..3066c5b8c2a 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, KeywordsCollectFn, 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 +427,23 @@ impl From<Color> for RGBAColor {
     }
 }
 
+impl SpecifiedValueInfo for Color {
+    const SUPPORTED_TYPES: u8 = CssType::COLOR;
+
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        // We are not going to insert all the color names here. Caller and
+        // devtools should take care of them. XXX Actually, transparent
+        // should probably be handled that way as well.
+        // XXX `currentColor` should really be `currentcolor`. But let's
+        // keep it consistent with the old system for now.
+        f(&["rgb", "rgba", "hsl", "hsla", "currentColor", "transparent"]);
+    }
+}
+
 /// 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..8ec4354ab7a 100644
--- a/components/style/values/specified/font.rs
+++ b/components/style/values/specified/font.rs
@@ -15,7 +15,9 @@ use malloc_size_of::{MallocSizeOf, MallocSizeOfOps};
 use parser::{Parse, ParserContext};
 use properties::longhands::system_font::SystemFont;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, KeywordsCollectFn, ParseError};
+use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
+use style_traits::values::SequenceWriter;
 use values::CustomIdent;
 use values::computed::{Angle as ComputedAngle, Percentage as ComputedPercentage};
 use values::computed::{font as computed, Context, Length, NonNegativeLength, ToComputedValue};
@@ -77,7 +79,7 @@ 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),
@@ -86,6 +88,7 @@ pub enum FontWeight {
     /// Lighter variant
     Lighter,
     /// System font variant.
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -154,7 +157,7 @@ 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:
     ///
@@ -333,10 +336,12 @@ 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),
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -378,15 +383,18 @@ 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),
+    #[css(skip)]
     System(SystemFont),
 }
 
 /// 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 +509,7 @@ 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.
@@ -522,6 +530,7 @@ pub enum FontSize {
     /// font-size: larger
     Larger,
     /// Derived from a specified system font.
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -538,6 +547,7 @@ pub enum FontFamily {
     #[css(comma)]
     Values(#[css(iterable)] FontFamilyList),
     /// System font
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -602,6 +612,8 @@ 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 +631,7 @@ 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
@@ -627,6 +639,7 @@ pub enum FontSizeAdjust {
     /// Number variant
     Number(Number),
     /// system font
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -704,21 +717,6 @@ impl KeywordInfo {
     }
 }
 
-impl KeywordSize {
-    /// Parses a keyword size.
-    pub fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
-        try_match_ident_ignore_ascii_case! { input,
-            "xx-small" => Ok(KeywordSize::XXSmall),
-            "x-small" => Ok(KeywordSize::XSmall),
-            "small" => Ok(KeywordSize::Small),
-            "medium" => Ok(KeywordSize::Medium),
-            "large" => Ok(KeywordSize::Large),
-            "x-large" => Ok(KeywordSize::XLarge),
-            "xx-large" => Ok(KeywordSize::XXLarge),
-        }
-    }
-}
-
 /// This is the ratio applied for font-size: larger
 /// and smaller by both Firefox and Chrome
 const LARGER_FONT_SIZE_RATIO: f32 = 1.2;
@@ -1079,7 +1077,7 @@ 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 +1102,7 @@ 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]>,
@@ -1125,12 +1123,13 @@ 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
     Value(VariantAlternatesList),
     /// Use system font glyph
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -1263,33 +1262,84 @@ impl Parse for FontVariantAlternates {
     }
 }
 
-bitflags! {
-    #[derive(MallocSizeOf)]
-    /// Vairants for east asian variant
-    pub struct VariantEastAsian: u16 {
-        /// None of the features
-        const NORMAL = 0;
-        /// Enables rendering of JIS78 forms (OpenType feature: jp78)
-        const JIS78 = 0x01;
-        /// Enables rendering of JIS83 forms (OpenType feature: jp83).
-        const JIS83 = 0x02;
-        /// Enables rendering of JIS90 forms (OpenType feature: jp90).
-        const JIS90 = 0x04;
-        /// Enables rendering of JIS2004 forms (OpenType feature: jp04).
-        const JIS04 = 0x08;
-        /// Enables rendering of simplified forms (OpenType feature: smpl).
-        const SIMPLIFIED = 0x10;
-        /// Enables rendering of traditional forms (OpenType feature: trad).
-        const TRADITIONAL = 0x20;
-        /// Enables rendering of full-width variants (OpenType feature: fwid).
-        const FULL_WIDTH = 0x40;
-        /// Enables rendering of proportionally-spaced variants (OpenType feature: pwid).
-        const PROPORTIONAL_WIDTH = 0x80;
-        /// Enables display of ruby variant glyphs (OpenType feature: ruby).
-        const RUBY = 0x100;
+macro_rules! impl_variant_east_asian {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $gecko:ident = $value:expr,
+        )+
+    } => {
+        bitflags! {
+            #[derive(MallocSizeOf)]
+            /// Vairants for east asian variant
+            pub struct VariantEastAsian: u16 {
+                /// None of the features
+                const NORMAL = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+            }
+        }
+
+        impl ToCss for VariantEastAsian {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("normal");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.intersects(VariantEastAsian::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
+        #[cfg(feature = "gecko")]
+        #[inline]
+        pub fn assert_variant_east_asian_matches() {
+            use gecko_bindings::structs;
+            $(
+                debug_assert_eq!(structs::$gecko as u16, VariantEastAsian::$ident.bits());
+            )+
+        }
+
+        impl SpecifiedValueInfo for VariantEastAsian {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["normal", $($css,)+]);
+            }
+        }
     }
 }
 
+impl_variant_east_asian! {
+    /// Enables rendering of JIS78 forms (OpenType feature: jp78)
+    JIS78 / "jis78" => NS_FONT_VARIANT_EAST_ASIAN_JIS78 = 0x01,
+    /// Enables rendering of JIS83 forms (OpenType feature: jp83).
+    JIS83 / "jis83" => NS_FONT_VARIANT_EAST_ASIAN_JIS83 = 0x02,
+    /// Enables rendering of JIS90 forms (OpenType feature: jp90).
+    JIS90 / "jis90" => NS_FONT_VARIANT_EAST_ASIAN_JIS90 = 0x04,
+    /// Enables rendering of JIS2004 forms (OpenType feature: jp04).
+    JIS04 / "jis04" => NS_FONT_VARIANT_EAST_ASIAN_JIS04 = 0x08,
+    /// Enables rendering of simplified forms (OpenType feature: smpl).
+    SIMPLIFIED / "simplified" => NS_FONT_VARIANT_EAST_ASIAN_SIMPLIFIED = 0x10,
+    /// Enables rendering of traditional forms (OpenType feature: trad).
+    TRADITIONAL / "traditional" => NS_FONT_VARIANT_EAST_ASIAN_TRADITIONAL = 0x20,
+    /// Enables rendering of full-width variants (OpenType feature: fwid).
+    FULL_WIDTH / "full-width" => NS_FONT_VARIANT_EAST_ASIAN_FULL_WIDTH = 0x40,
+    /// Enables rendering of proportionally-spaced variants (OpenType feature: pwid).
+    PROPORTIONAL_WIDTH / "proportional-width" => NS_FONT_VARIANT_EAST_ASIAN_PROP_WIDTH = 0x80,
+    /// Enables display of ruby variant glyphs (OpenType feature: ruby).
+    RUBY / "ruby" => NS_FONT_VARIANT_EAST_ASIAN_RUBY = 0x100,
+}
+
 #[cfg(feature = "gecko")]
 impl VariantEastAsian {
     /// Obtain a specified value from a Gecko keyword value
@@ -1305,83 +1355,17 @@ impl VariantEastAsian {
     }
 }
 
-impl ToCss for VariantEastAsian {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        if self.is_empty() {
-            return dest.write_str("normal");
-        }
-
-        let mut has_any = false;
-
-        macro_rules! write_value {
-            ($ident:path => $str:expr) => {
-                if self.intersects($ident) {
-                    if has_any {
-                        dest.write_str(" ")?;
-                    }
-                    has_any = true;
-                    dest.write_str($str)?;
-                }
-            };
-        }
-
-        write_value!(VariantEastAsian::JIS78 => "jis78");
-        write_value!(VariantEastAsian::JIS83 => "jis83");
-        write_value!(VariantEastAsian::JIS90 => "jis90");
-        write_value!(VariantEastAsian::JIS04 => "jis04");
-        write_value!(VariantEastAsian::SIMPLIFIED => "simplified");
-        write_value!(VariantEastAsian::TRADITIONAL => "traditional");
-        write_value!(VariantEastAsian::FULL_WIDTH => "full-width");
-        write_value!(VariantEastAsian::PROPORTIONAL_WIDTH => "proportional-width");
-        write_value!(VariantEastAsian::RUBY => "ruby");
-
-        debug_assert!(has_any);
-        Ok(())
-    }
-}
-
 #[cfg(feature = "gecko")]
 impl_gecko_keyword_conversions!(VariantEastAsian, u16);
 
-/// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
-#[cfg(feature = "gecko")]
-#[inline]
-pub fn assert_variant_east_asian_matches() {
-    use gecko_bindings::structs;
-
-    macro_rules! check_variant_east_asian {
-        ( $( $a:ident => $b:path),*, ) => {
-            if cfg!(debug_assertions) {
-                $(
-                    assert_eq!(structs::$a as u16, $b.bits());
-                )*
-            }
-        }
-    }
-
-    check_variant_east_asian! {
-        NS_FONT_VARIANT_EAST_ASIAN_FULL_WIDTH => VariantEastAsian::FULL_WIDTH,
-        NS_FONT_VARIANT_EAST_ASIAN_JIS04 => VariantEastAsian::JIS04,
-        NS_FONT_VARIANT_EAST_ASIAN_JIS78 => VariantEastAsian::JIS78,
-        NS_FONT_VARIANT_EAST_ASIAN_JIS83 => VariantEastAsian::JIS83,
-        NS_FONT_VARIANT_EAST_ASIAN_JIS90 => VariantEastAsian::JIS90,
-        NS_FONT_VARIANT_EAST_ASIAN_PROP_WIDTH => VariantEastAsian::PROPORTIONAL_WIDTH,
-        NS_FONT_VARIANT_EAST_ASIAN_RUBY => VariantEastAsian::RUBY,
-        NS_FONT_VARIANT_EAST_ASIAN_SIMPLIFIED => VariantEastAsian::SIMPLIFIED,
-        NS_FONT_VARIANT_EAST_ASIAN_TRADITIONAL => VariantEastAsian::TRADITIONAL,
-    }
-}
-
 #[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`
     Value(VariantEastAsian),
     /// System font variant
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -1485,34 +1469,88 @@ impl Parse for FontVariantEastAsian {
     }
 }
 
-bitflags! {
-    #[derive(MallocSizeOf)]
-    /// Variants of ligatures
-    pub struct VariantLigatures: u16 {
-        /// Specifies that common default features are enabled
-        const NORMAL = 0;
-        /// Specifies that all types of ligatures and contextual forms
-        /// covered by this property are explicitly disabled
-        const NONE = 0x01;
-        /// Enables display of common ligatures
-        const COMMON_LIGATURES = 0x02;
-        /// Disables display of common ligatures
-        const NO_COMMON_LIGATURES = 0x04;
-        /// Enables display of discretionary ligatures
-        const DISCRETIONARY_LIGATURES = 0x08;
-        /// Disables display of discretionary ligatures
-        const NO_DISCRETIONARY_LIGATURES = 0x10;
-        /// Enables display of historical ligatures
-        const HISTORICAL_LIGATURES = 0x20;
-        /// Disables display of historical ligatures
-        const NO_HISTORICAL_LIGATURES = 0x40;
-        /// Enables display of contextual alternates
-        const CONTEXTUAL = 0x80;
-        /// Disables display of contextual alternates
-        const NO_CONTEXTUAL = 0x100;
+macro_rules! impl_variant_ligatures {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $gecko:ident = $value:expr,
+        )+
+    } => {
+        bitflags! {
+            #[derive(MallocSizeOf)]
+            /// Variants of ligatures
+            pub struct VariantLigatures: u16 {
+                /// Specifies that common default features are enabled
+                const NORMAL = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+            }
+        }
+
+        impl ToCss for VariantLigatures {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("normal");
+                }
+                if self.contains(VariantLigatures::NONE) {
+                    return dest.write_str("none");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.intersects(VariantLigatures::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
+        #[cfg(feature = "gecko")]
+        #[inline]
+        pub fn assert_variant_ligatures_matches() {
+            use gecko_bindings::structs;
+            $(
+                debug_assert_eq!(structs::$gecko as u16, VariantLigatures::$ident.bits());
+            )+
+        }
+
+        impl SpecifiedValueInfo for VariantLigatures {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["normal", $($css,)+]);
+            }
+        }
     }
 }
 
+impl_variant_ligatures! {
+    /// Specifies that all types of ligatures and contextual forms
+    /// covered by this property are explicitly disabled
+    NONE / "none" => NS_FONT_VARIANT_LIGATURES_NONE = 0x01,
+    /// Enables display of common ligatures
+    COMMON_LIGATURES / "common-ligatures" => NS_FONT_VARIANT_LIGATURES_COMMON = 0x02,
+    /// Disables display of common ligatures
+    NO_COMMON_LIGATURES / "no-common-ligatures" => NS_FONT_VARIANT_LIGATURES_NO_COMMON = 0x04,
+    /// Enables display of discretionary ligatures
+    DISCRETIONARY_LIGATURES / "discretionary-ligatures" => NS_FONT_VARIANT_LIGATURES_DISCRETIONARY = 0x08,
+    /// Disables display of discretionary ligatures
+    NO_DISCRETIONARY_LIGATURES / "no-discretionary-ligatures" => NS_FONT_VARIANT_LIGATURES_NO_DISCRETIONARY = 0x10,
+    /// Enables display of historical ligatures
+    HISTORICAL_LIGATURES / "historical-ligatures" => NS_FONT_VARIANT_LIGATURES_HISTORICAL = 0x20,
+    /// Disables display of historical ligatures
+    NO_HISTORICAL_LIGATURES / "no-historical-ligatures" => NS_FONT_VARIANT_LIGATURES_NO_HISTORICAL = 0x40,
+    /// Enables display of contextual alternates
+    CONTEXTUAL / "contextual" => NS_FONT_VARIANT_LIGATURES_CONTEXTUAL = 0x80,
+    /// Disables display of contextual alternates
+    NO_CONTEXTUAL / "no-contextual" => NS_FONT_VARIANT_LIGATURES_NO_CONTEXTUAL = 0x100,
+}
+
 #[cfg(feature = "gecko")]
 impl VariantLigatures {
     /// Obtain a specified value from a Gecko keyword value
@@ -1528,86 +1566,18 @@ impl VariantLigatures {
     }
 }
 
-impl ToCss for VariantLigatures {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        if self.is_empty() {
-            return dest.write_str("normal");
-        }
-        if self.contains(VariantLigatures::NONE) {
-            return dest.write_str("none");
-        }
-
-        let mut has_any = false;
-
-        macro_rules! write_value {
-            ($ident:path => $str:expr) => {
-                if self.intersects($ident) {
-                    if has_any {
-                        dest.write_str(" ")?;
-                    }
-                    has_any = true;
-                    dest.write_str($str)?;
-                }
-            };
-        }
-
-        write_value!(VariantLigatures::COMMON_LIGATURES => "common-ligatures");
-        write_value!(VariantLigatures::NO_COMMON_LIGATURES => "no-common-ligatures");
-        write_value!(VariantLigatures::DISCRETIONARY_LIGATURES => "discretionary-ligatures");
-        write_value!(VariantLigatures::NO_DISCRETIONARY_LIGATURES => "no-discretionary-ligatures");
-        write_value!(VariantLigatures::HISTORICAL_LIGATURES => "historical-ligatures");
-        write_value!(VariantLigatures::NO_HISTORICAL_LIGATURES => "no-historical-ligatures");
-        write_value!(VariantLigatures::CONTEXTUAL => "contextual");
-        write_value!(VariantLigatures::NO_CONTEXTUAL => "no-contextual");
-
-        debug_assert!(has_any);
-        Ok(())
-    }
-}
-
 #[cfg(feature = "gecko")]
 impl_gecko_keyword_conversions!(VariantLigatures, u16);
 
-/// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
-#[cfg(feature = "gecko")]
-#[inline]
-pub fn assert_variant_ligatures_matches() {
-    use gecko_bindings::structs;
-
-    macro_rules! check_variant_ligatures {
-        ( $( $a:ident => $b:path),*, ) => {
-            if cfg!(debug_assertions) {
-                $(
-                    assert_eq!(structs::$a as u16, $b.bits());
-                )*
-            }
-        }
-    }
-
-    check_variant_ligatures! {
-        NS_FONT_VARIANT_LIGATURES_NONE => VariantLigatures::NONE,
-        NS_FONT_VARIANT_LIGATURES_COMMON => VariantLigatures::COMMON_LIGATURES,
-        NS_FONT_VARIANT_LIGATURES_NO_COMMON => VariantLigatures::NO_COMMON_LIGATURES,
-        NS_FONT_VARIANT_LIGATURES_DISCRETIONARY => VariantLigatures::DISCRETIONARY_LIGATURES,
-        NS_FONT_VARIANT_LIGATURES_NO_DISCRETIONARY => VariantLigatures::NO_DISCRETIONARY_LIGATURES,
-        NS_FONT_VARIANT_LIGATURES_HISTORICAL => VariantLigatures::HISTORICAL_LIGATURES,
-        NS_FONT_VARIANT_LIGATURES_NO_HISTORICAL => VariantLigatures::NO_HISTORICAL_LIGATURES,
-        NS_FONT_VARIANT_LIGATURES_CONTEXTUAL => VariantLigatures::CONTEXTUAL,
-        NS_FONT_VARIANT_LIGATURES_NO_CONTEXTUAL => VariantLigatures::NO_CONTEXTUAL,
-    }
-}
-
 #[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 {
     /// Value variant with `variant-ligatures`
     Value(VariantLigatures),
     /// System font variant
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -1721,31 +1691,82 @@ impl Parse for FontVariantLigatures {
     }
 }
 
-bitflags! {
-    #[derive(MallocSizeOf)]
-    /// Vairants of numeric values
-    pub struct VariantNumeric: u8 {
-        /// None of other variants are enabled.
-        const NORMAL = 0;
-        /// Enables display of lining numerals.
-        const LINING_NUMS = 0x01;
-        /// Enables display of old-style numerals.
-        const OLDSTYLE_NUMS = 0x02;
-        /// Enables display of proportional numerals.
-        const PROPORTIONAL_NUMS = 0x04;
-        /// Enables display of tabular numerals.
-        const TABULAR_NUMS = 0x08;
-        /// Enables display of lining diagonal fractions.
-        const DIAGONAL_FRACTIONS = 0x10;
-        /// Enables display of lining stacked fractions.
-        const STACKED_FRACTIONS = 0x20;
-        /// Enables display of letter forms used with ordinal numbers.
-        const ORDINAL = 0x80;
-        /// Enables display of slashed zeros.
-        const SLASHED_ZERO = 0x40;
+macro_rules! impl_variant_numeric {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $gecko:ident = $value:expr,
+        )+
+    } => {
+        bitflags! {
+            #[derive(MallocSizeOf)]
+            /// Vairants of numeric values
+            pub struct VariantNumeric: u8 {
+                /// None of other variants are enabled.
+                const NORMAL = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+            }
+        }
+
+        impl ToCss for VariantNumeric {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("normal");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.intersects(VariantNumeric::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        /// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
+        #[cfg(feature = "gecko")]
+        #[inline]
+        pub fn assert_variant_numeric_matches() {
+            use gecko_bindings::structs;
+            $(
+                debug_assert_eq!(structs::$gecko as u8, VariantNumeric::$ident.bits());
+            )+
+        }
+
+        impl SpecifiedValueInfo for VariantNumeric {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["normal", $($css,)+]);
+            }
+        }
     }
 }
 
+impl_variant_numeric! {
+    /// Enables display of lining numerals.
+    LINING_NUMS / "lining-nums" => NS_FONT_VARIANT_NUMERIC_LINING = 0x01,
+    /// Enables display of old-style numerals.
+    OLDSTYLE_NUMS / "oldstyle-nums" => NS_FONT_VARIANT_NUMERIC_OLDSTYLE = 0x02,
+    /// Enables display of proportional numerals.
+    PROPORTIONAL_NUMS / "proportional-nums" => NS_FONT_VARIANT_NUMERIC_PROPORTIONAL = 0x04,
+    /// Enables display of tabular numerals.
+    TABULAR_NUMS / "tabular-nums" => NS_FONT_VARIANT_NUMERIC_TABULAR = 0x08,
+    /// Enables display of lining diagonal fractions.
+    DIAGONAL_FRACTIONS / "diagonal-fractions" => NS_FONT_VARIANT_NUMERIC_DIAGONAL_FRACTIONS = 0x10,
+    /// Enables display of lining stacked fractions.
+    STACKED_FRACTIONS / "stacked-fractions" => NS_FONT_VARIANT_NUMERIC_STACKED_FRACTIONS = 0x20,
+    /// Enables display of letter forms used with ordinal numbers.
+    ORDINAL / "ordinal" => NS_FONT_VARIANT_NUMERIC_ORDINAL = 0x80,
+    /// Enables display of slashed zeros.
+    SLASHED_ZERO / "slashed-zero" => NS_FONT_VARIANT_NUMERIC_SLASHZERO = 0x40,
+}
+
 #[cfg(feature = "gecko")]
 impl VariantNumeric {
     /// Obtain a specified value from a Gecko keyword value
@@ -1761,81 +1782,17 @@ impl VariantNumeric {
     }
 }
 
-impl ToCss for VariantNumeric {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        if self.is_empty() {
-            return dest.write_str("normal");
-        }
-
-        let mut has_any = false;
-
-        macro_rules! write_value {
-            ($ident:path => $str:expr) => {
-                if self.intersects($ident) {
-                    if has_any {
-                        dest.write_str(" ")?;
-                    }
-                    has_any = true;
-                    dest.write_str($str)?;
-                }
-            };
-        }
-
-        write_value!(VariantNumeric::LINING_NUMS => "lining-nums");
-        write_value!(VariantNumeric::OLDSTYLE_NUMS => "oldstyle-nums");
-        write_value!(VariantNumeric::PROPORTIONAL_NUMS => "proportional-nums");
-        write_value!(VariantNumeric::TABULAR_NUMS => "tabular-nums");
-        write_value!(VariantNumeric::DIAGONAL_FRACTIONS => "diagonal-fractions");
-        write_value!(VariantNumeric::STACKED_FRACTIONS => "stacked-fractions");
-        write_value!(VariantNumeric::SLASHED_ZERO => "slashed-zero");
-        write_value!(VariantNumeric::ORDINAL => "ordinal");
-
-        debug_assert!(has_any);
-        Ok(())
-    }
-}
-
 #[cfg(feature = "gecko")]
 impl_gecko_keyword_conversions!(VariantNumeric, u8);
 
-/// Asserts that all variant-east-asian matches its NS_FONT_VARIANT_EAST_ASIAN_* value.
-#[cfg(feature = "gecko")]
-#[inline]
-pub fn assert_variant_numeric_matches() {
-    use gecko_bindings::structs;
-
-    macro_rules! check_variant_numeric {
-        ( $( $a:ident => $b:path),*, ) => {
-            if cfg!(debug_assertions) {
-                $(
-                    assert_eq!(structs::$a as u8, $b.bits());
-                )*
-            }
-        }
-    }
-
-    check_variant_numeric! {
-        NS_FONT_VARIANT_NUMERIC_LINING => VariantNumeric::LINING_NUMS,
-        NS_FONT_VARIANT_NUMERIC_OLDSTYLE => VariantNumeric::OLDSTYLE_NUMS,
-        NS_FONT_VARIANT_NUMERIC_PROPORTIONAL => VariantNumeric::PROPORTIONAL_NUMS,
-        NS_FONT_VARIANT_NUMERIC_TABULAR => VariantNumeric::TABULAR_NUMS,
-        NS_FONT_VARIANT_NUMERIC_DIAGONAL_FRACTIONS => VariantNumeric::DIAGONAL_FRACTIONS,
-        NS_FONT_VARIANT_NUMERIC_STACKED_FRACTIONS => VariantNumeric::STACKED_FRACTIONS,
-        NS_FONT_VARIANT_NUMERIC_SLASHZERO => VariantNumeric::SLASHED_ZERO,
-        NS_FONT_VARIANT_NUMERIC_ORDINAL => VariantNumeric::ORDINAL,
-    }
-}
-
 #[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`
     Value(VariantNumeric),
     /// System font
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -1938,11 +1895,12 @@ 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),
     /// System font
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -1981,16 +1939,19 @@ 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 {
     /// If a `font-weight` is requested that the font family does not contain,
     /// the user agent may synthesize the requested weight from the weights
     /// that do exist in the font family.
+    #[value_info(represents_keyword)]
     pub weight: bool,
     /// If a font-style is requested that the font family does not contain,
     /// the user agent may synthesize the requested style from the normal face in the font family.
+    #[value_info(represents_keyword)]
     pub style: bool,
 }
 
@@ -2079,7 +2040,7 @@ 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 {
@@ -2092,6 +2053,7 @@ pub enum FontLanguageOverride {
     /// the language system implied by the language of the element
     Override(Box<str>),
     /// Use system font
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -2169,11 +2131,12 @@ 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),
     /// System font
+    #[css(skip)]
     System(SystemFont),
 }
 
@@ -2254,7 +2217,8 @@ 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 +2235,8 @@ 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 +2262,7 @@ 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 +2289,7 @@ 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 +2324,8 @@ 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..f00b9b53f3c 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, KeywordsCollectFn, ParseError};
+use style_traits::{StyleParseErrorKind, SpecifiedValueInfo, ToCss};
 use values::{Either, None_};
 #[cfg(feature = "gecko")]
 use values::computed::{Context, Position as ComputedPosition, ToComputedValue};
@@ -54,6 +55,29 @@ pub type Gradient = generic::Gradient<
     Angle,
 >;
 
+impl SpecifiedValueInfo for Gradient {
+    const SUPPORTED_TYPES: u8 = CssType::GRADIENT;
+
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        // This list here should keep sync with that in Gradient::parse.
+        f(&[
+          "linear-gradient",
+          "-webkit-linear-gradient",
+          "-moz-linear-gradient",
+          "repeating-linear-gradient",
+          "-webkit-repeating-linear-gradient",
+          "-moz-repeating-linear-gradient",
+          "radial-gradient",
+          "-webkit-radial-gradient",
+          "-moz-radial-gradient",
+          "repeating-radial-gradient",
+          "-webkit-repeating-radial-gradient",
+          "-moz-repeating-radial-gradient",
+          "-webkit-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..c7756f974f2 100644
--- a/components/style/values/specified/inherited_box.rs
+++ b/components/style/values/specified/inherited_box.rs
@@ -15,12 +15,13 @@ 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>,
 
     /// Whether or not "flip" was specified
+    #[value_info(other_values = "flip,from-image")]
     pub flipped: bool,
 }
 
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..ae61bb1ae9c 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),
@@ -77,8 +78,10 @@ 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)]
-pub struct Quotes(pub Box<[(Box<str>, Box<str>)]>);
+/// FIXME This can probably derive ToCss.
+#[derive(Clone, Debug, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
+pub struct Quotes(#[css(if_empty = "none")] pub Box<[(Box<str>, Box<str>)]>);
 
 impl ToCss for Quotes {
     fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index 20b49596ab7..3f89dae0053 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>;
 
@@ -562,8 +568,9 @@ 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
+#[css(function = "rect")]
 pub struct ClipRect {
     /// <top> (<length> | <auto>)
     pub top: Option<Length>,
@@ -751,7 +758,9 @@ impl AllowQuirks {
 /// An attr(...) rule
 ///
 /// `[namespace? `|`]? ident`
-#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, ToComputedValue)]
+#[derive(Clone, Debug, Eq, MallocSizeOf, PartialEq, SpecifiedValueInfo,
+         ToComputedValue)]
+#[css(function)]
 pub struct Attr {
     /// Optional namespace prefix and URL.
     pub namespace: Option<(Prefix, Namespace)>,
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/pointing.rs b/components/style/values/specified/pointing.rs
index d8da1305efb..cf718a1fd9d 100644
--- a/components/style/values/specified/pointing.rs
+++ b/components/style/values/specified/pointing.rs
@@ -8,44 +8,15 @@
 
 use cssparser::Parser;
 use parser::{Parse, ParserContext};
-use style_traits::ParseError;
+use style_traits::{ParseError, StyleParseErrorKind};
 use style_traits::cursor::CursorKind;
-use values::generics::pointing::CaretColor as GenericCaretColor;
+use values::generics::pointing as generics;
+use values::specified::Number;
 use values::specified::color::Color;
-#[cfg(feature = "gecko")]
 use values::specified::url::SpecifiedImageUrl;
 
-/// The specified value for the `cursor` property.
-///
-/// https://drafts.csswg.org/css-ui/#cursor
-#[cfg(feature = "servo")]
-#[derive(Clone, Copy, Debug, MallocSizeOf, PartialEq, ToComputedValue, ToCss)]
-pub struct Cursor(pub CursorKind);
-
-/// The specified value for the `cursor` property.
-///
-/// https://drafts.csswg.org/css-ui/#cursor
-#[cfg(feature = "gecko")]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
-pub struct Cursor {
-    /// The parsed images for the cursor.
-    pub images: Box<[CursorImage]>,
-    /// The kind of the cursor [default | help | ...].
-    pub keyword: CursorKind,
-}
-
-/// The specified value for the `image cursors`.
-#[cfg(feature = "gecko")]
-#[derive(Clone, Debug, MallocSizeOf, PartialEq, ToComputedValue)]
-pub struct CursorImage {
-    /// The url to parse images from.
-    pub url: SpecifiedImageUrl,
-    /// The <x> and <y> coordinates.
-    pub hotspot: Option<(f32, f32)>,
-}
-
 /// A specified value for the `caret-color` property.
-pub type CaretColor = GenericCaretColor<Color>;
+pub type CaretColor = generics::CaretColor<Color>;
 
 impl Parse for CaretColor {
     fn parse<'i, 't>(
@@ -53,8 +24,63 @@ impl Parse for CaretColor {
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
         if input.try(|i| i.expect_ident_matching("auto")).is_ok() {
-            return Ok(GenericCaretColor::Auto);
+            return Ok(generics::CaretColor::Auto);
         }
-        Ok(GenericCaretColor::Color(Color::parse(context, input)?))
+        Ok(generics::CaretColor::Color(Color::parse(context, input)?))
+    }
+}
+
+/// A specified value for the `cursor` property.
+pub type Cursor = generics::Cursor<CursorImage>;
+
+/// A specified value for item of `image cursors`.
+pub type CursorImage = generics::CursorImage<SpecifiedImageUrl, Number>;
+
+impl Parse for Cursor {
+    /// cursor: [<url> [<number> <number>]?]# [auto | default | ...]
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let mut images = vec![];
+        loop {
+            match input.try(|input| CursorImage::parse(context, input)) {
+                Ok(image) => images.push(image),
+                Err(_) => break,
+            }
+            input.expect_comma()?;
+        }
+        Ok(Self {
+            images: images.into_boxed_slice(),
+            keyword: CursorKind::parse(context, input)?,
+        })
+    }
+}
+
+impl Parse for CursorKind {
+    fn parse<'i, 't>(
+        _context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        let location = input.current_source_location();
+        let ident = input.expect_ident()?;
+        CursorKind::from_css_keyword(&ident).map_err(|_| {
+            location.new_custom_error(StyleParseErrorKind::UnspecifiedError)
+        })
+    }
+}
+
+impl Parse for CursorImage {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Ok(Self {
+            url: SpecifiedImageUrl::parse(context, input)?,
+            hotspot: match input.try(|input| Number::parse(context, input)) {
+                Ok(number) => Some((number, Number::parse(context, input)?)),
+                Err(_) => None,
+            },
+        })
     }
 }
diff --git a/components/style/values/specified/position.rs b/components/style/values/specified/position.rs
index d82240a3228..0f2669f0a02 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,
@@ -420,13 +423,15 @@ 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 {
     /// Specifiy how auto-placement algorithm fills each `row` or `column` in turn
     pub autoflow: AutoFlow,
     /// Specify use `dense` packing algorithm or not
+    #[value_info(represents_keyword)]
     pub dense: bool,
 }
 
@@ -533,7 +538,7 @@ 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 +644,8 @@ 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 +660,7 @@ 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..70947ac0826 100644
--- a/components/style/values/specified/text.rs
+++ b/components/style/values/specified/text.rs
@@ -9,7 +9,9 @@ use parser::{Parse, ParserContext};
 use properties::longhands::writing_mode::computed_value::T as SpecifiedWritingMode;
 use selectors::parser::SelectorParseErrorKind;
 use std::fmt::{self, Write};
-use style_traits::{CssWriter, ParseError, StyleParseErrorKind, ToCss};
+use style_traits::{CssWriter, KeywordsCollectFn, ParseError};
+use style_traits::{SpecifiedValueInfo, StyleParseErrorKind, ToCss};
+use style_traits::values::SequenceWriter;
 use unicode_segmentation::UnicodeSegmentation;
 use values::computed::{Context, ToComputedValue};
 use values::computed::text::LineHeight as ComputedLineHeight;
@@ -158,7 +160,7 @@ 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 +194,7 @@ 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.
@@ -251,32 +253,117 @@ impl ToComputedValue for TextOverflow {
     }
 }
 
-bitflags! {
-    #[derive(MallocSizeOf, ToComputedValue)]
-    /// Specified keyword values for the text-decoration-line property.
-    pub struct TextDecorationLine: u8 {
-        /// No text decoration line is specified
-        const NONE = 0;
-        /// Underline
-        const UNDERLINE = 0x01;
-        /// Overline
-        const OVERLINE = 0x02;
-        /// Line through
-        const LINE_THROUGH = 0x04;
-        /// Blink
-        const BLINK = 0x08;
-        #[cfg(feature = "gecko")]
-        /// Only set by presentation attributes
-        ///
-        /// Setting this will mean that text-decorations use the color
-        /// specified by `color` in quirks mode.
-        ///
-        /// For example, this gives <a href=foo><font color="red">text</font></a>
-        /// a red text decoration
-        const COLOR_OVERRIDE = 0x10;
+macro_rules! impl_text_decoration_line {
+    {
+        $(
+            $(#[$($meta:tt)+])*
+            $ident:ident / $css:expr => $value:expr,
+        )+
+    } => {
+        bitflags! {
+            #[derive(MallocSizeOf, ToComputedValue)]
+            /// Specified keyword values for the text-decoration-line property.
+            pub struct TextDecorationLine: u8 {
+                /// No text decoration line is specified
+                const NONE = 0;
+                $(
+                    $(#[$($meta)+])*
+                    const $ident = $value;
+                )+
+                #[cfg(feature = "gecko")]
+                /// Only set by presentation attributes
+                ///
+                /// Setting this will mean that text-decorations use the color
+                /// specified by `color` in quirks mode.
+                ///
+                /// For example, this gives <a href=foo><font color="red">text</font></a>
+                /// a red text decoration
+                const COLOR_OVERRIDE = 0x10;
+            }
+        }
+
+        impl Parse for TextDecorationLine {
+            /// none | [ underline || overline || line-through || blink ]
+            fn parse<'i, 't>(
+                _context: &ParserContext,
+                input: &mut Parser<'i, 't>,
+            ) -> Result<TextDecorationLine, ParseError<'i>> {
+                let mut result = TextDecorationLine::NONE;
+                if input
+                    .try(|input| input.expect_ident_matching("none"))
+                    .is_ok()
+                {
+                    return Ok(result);
+                }
+
+                loop {
+                    let result = input.try(|input| {
+                        let ident = input.expect_ident().map_err(|_| ())?;
+                        match_ignore_ascii_case! { ident,
+                            $(
+                                $css => {
+                                    if result.contains(TextDecorationLine::$ident) {
+                                        Err(())
+                                    } else {
+                                        result.insert(TextDecorationLine::$ident);
+                                        Ok(())
+                                    }
+                                }
+                            )+
+                            _ => Err(()),
+                        }
+                    });
+                    if result.is_err() {
+                        break;
+                    }
+                }
+
+                if !result.is_empty() {
+                    Ok(result)
+                } else {
+                    Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
+                }
+            }
+        }
+
+        impl ToCss for TextDecorationLine {
+            fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+            where
+                W: Write,
+            {
+                if self.is_empty() {
+                    return dest.write_str("none");
+                }
+
+                let mut writer = SequenceWriter::new(dest, " ");
+                $(
+                    if self.contains(TextDecorationLine::$ident) {
+                        writer.raw_item($css)?;
+                    }
+                )+
+                Ok(())
+            }
+        }
+
+        impl SpecifiedValueInfo for TextDecorationLine {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&["none", $($css,)+]);
+            }
+        }
     }
 }
 
+impl_text_decoration_line! {
+    /// Underline
+    UNDERLINE / "underline" => 1 << 0,
+    /// Overline
+    OVERLINE / "overline" => 1 << 1,
+    /// Line through
+    LINE_THROUGH / "line-through" => 1 << 2,
+    /// Blink
+    BLINK / "blink" => 1 << 3,
+}
+
 #[cfg(feature = "gecko")]
 impl_bitflags_conversions!(TextDecorationLine);
 
@@ -288,79 +375,18 @@ impl TextDecorationLine {
     }
 }
 
-impl Parse for TextDecorationLine {
-    /// none | [ underline || overline || line-through || blink ]
-    fn parse<'i, 't>(
-        _context: &ParserContext,
-        input: &mut Parser<'i, 't>,
-    ) -> Result<TextDecorationLine, ParseError<'i>> {
-        let mut result = TextDecorationLine::NONE;
-        if input
-            .try(|input| input.expect_ident_matching("none"))
-            .is_ok()
-        {
-            return Ok(result);
-        }
-
-        loop {
-            let result = input.try(|input| {
-                let ident = input.expect_ident().map_err(|_| ())?;
-                match_ignore_ascii_case! { ident,
-                    "underline" => {
-                        if result.contains(TextDecorationLine::UNDERLINE) {
-                            Err(())
-                        } else {
-                            result.insert(TextDecorationLine::UNDERLINE);
-                            Ok(())
-                        }
-                    }
-                    "overline" => {
-                        if result.contains(TextDecorationLine::OVERLINE) {
-                            Err(())
-                        } else {
-                            result.insert(TextDecorationLine::OVERLINE);
-                            Ok(())
-                        }
-                    }
-                    "line-through" => {
-                        if result.contains(TextDecorationLine::LINE_THROUGH) {
-                            Err(())
-                        } else {
-                            result.insert(TextDecorationLine::LINE_THROUGH);
-                            Ok(())
-                        }
-                    }
-                    "blink" => {
-                        if result.contains(TextDecorationLine::BLINK) {
-                            Err(())
-                        } else {
-                            result.insert(TextDecorationLine::BLINK);
-                            Ok(())
-                        }
-                    }
-                    _ => Err(()),
-                }
-            });
-            if result.is_err() {
-                break;
-            }
-        }
-
-        if !result.is_empty() {
-            Ok(result)
-        } else {
-            Err(input.new_custom_error(StyleParseErrorKind::UnspecifiedError))
-        }
-    }
-}
-
 macro_rules! define_text_align_keyword {
-    ($($name: ident => $discriminant: expr,)+) => {
+    ($(
+        $(#[$($meta:tt)+])*
+        $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 {
             $(
+                $(#[$($meta)+])*
                 $name = $discriminant,
             )+
         }
@@ -391,6 +417,7 @@ define_text_align_keyword! {
     MozCenter => 6,
     MozLeft => 7,
     MozRight => 8,
+    #[css(skip)]
     Char => 10,
 }
 
@@ -417,7 +444,7 @@ 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, ToCss)]
 pub enum TextAlign {
     /// Keyword value of text-align property.
     Keyword(TextAlignKeyword),
@@ -429,6 +456,7 @@ pub enum TextAlign {
     /// only set directly on the elements and it has a different handling
     /// unlike other values.
     #[cfg(feature = "gecko")]
+    #[css(skip)]
     MozCenterOrInherit,
 }
 
@@ -453,21 +481,6 @@ impl Parse for TextAlign {
     }
 }
 
-impl ToCss for TextAlign {
-    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
-    where
-        W: Write,
-    {
-        match *self {
-            TextAlign::Keyword(key) => key.to_css(dest),
-            #[cfg(feature = "gecko")]
-            TextAlign::MatchParent => dest.write_str("match-parent"),
-            #[cfg(feature = "gecko")]
-            TextAlign::MozCenterOrInherit => Ok(()),
-        }
-    }
-}
-
 impl TextAlign {
     /// Convert an enumerated value coming from Gecko to a `TextAlign`.
     #[cfg(feature = "gecko")]
@@ -534,7 +547,7 @@ 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 +558,7 @@ 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 +587,8 @@ 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 +597,8 @@ 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 +724,8 @@ 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 +734,8 @@ 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 +744,8 @@ 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..835d505836c 100644
--- a/components/style/values/specified/transform.rs
+++ b/components/style/values/specified/transform.rs
@@ -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,
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..88f0bbadfb1 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, value_info))]
+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..7727d6b89bb 100644
--- a/components/style_derive/parse.rs
+++ b/components/style_derive/parse.rs
@@ -19,7 +19,11 @@ 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());
+        if variant_attrs.skip {
+            return match_body;
+        }
+
         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..11ad7a0d1b4
--- /dev/null
+++ b/components/style_derive/specified_value_info.rs
@@ -0,0 +1,181 @@
+/* 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, Ident, Type};
+use to_css::{CssFieldAttrs, CssInputAttrs, CssVariantAttrs};
+
+pub fn derive(mut input: DeriveInput) -> Tokens {
+    let css_attrs = cg::parse_input_attrs::<CssInputAttrs>(&input);
+    let mut types = vec![];
+    let mut values = vec![];
+
+    let input_ident = input.ident;
+    let input_name = || cg::to_css_identifier(input_ident.as_ref());
+    if let Some(function) = css_attrs.function {
+        values.push(function.explicit().unwrap_or_else(input_name));
+        // If the whole value is wrapped in a function, value types of
+        // its fields should not be propagated.
+    } else {
+        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 css_attrs = cg::parse_variant_attrs::<CssVariantAttrs>(&v);
+                    let info_attrs = cg::parse_variant_attrs::<ValueInfoVariantAttrs>(&v);
+                    if css_attrs.skip {
+                        continue;
+                    }
+                    if let Some(aliases) = css_attrs.aliases {
+                        for alias in aliases.split(",") {
+                            values.push(alias.to_string());
+                        }
+                    }
+                    if let Some(other_values) = info_attrs.other_values {
+                        for value in other_values.split(",") {
+                            values.push(value.to_string());
+                        }
+                    }
+                    let ident = &v.ident;
+                    let variant_name = || cg::to_css_identifier(ident.as_ref());
+                    if info_attrs.starts_with_keyword {
+                        values.push(variant_name());
+                        continue;
+                    }
+                    if let Some(keyword) = css_attrs.keyword {
+                        values.push(keyword);
+                        continue;
+                    }
+                    if let Some(function) = css_attrs.function {
+                        values.push(function.explicit().unwrap_or_else(variant_name));
+                    } else {
+                        if !derive_struct_fields(&v.fields, &mut types, &mut values) {
+                            values.push(variant_name());
+                        }
+                    }
+                }
+            }
+            Data::Struct(ref s) => {
+                if !derive_struct_fields(&s.fields, &mut types, &mut values) {
+                    values.push(input_name());
+                }
+            }
+            Data::Union(_) => unreachable!("union is not supported"),
+        }
+    }
+
+    let info_attrs = cg::parse_input_attrs::<ValueInfoInputAttrs>(&input);
+    if let Some(other_values) = info_attrs.other_values {
+        for value in other_values.split(",") {
+            values.push(value.to_string());
+        }
+    }
+
+    let mut types_value = quote!(0);
+    types_value.append_all(types.iter().map(|ty| quote! {
+        | <#ty as ::style_traits::SpecifiedValueInfo>::SUPPORTED_TYPES
+    }));
+
+    let mut nested_collects = quote!();
+    nested_collects.append_all(types.iter().map(|ty| quote! {
+        <#ty as ::style_traits::SpecifiedValueInfo>::collect_completion_keywords(_f);
+    }));
+
+    if let Some(ty) = info_attrs.ty {
+        types_value.append_all(quote! {
+            | ::style_traits::CssType::#ty
+        });
+    }
+
+    let append_values = if values.is_empty() {
+        quote!()
+    } else {
+        let mut value_list = quote!();
+        value_list.append_separated(values.iter(), quote! { , });
+        quote! { _f(&[#value_list]); }
+    };
+
+    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 collect_completion_keywords(_f: &mut FnMut(&[&'static str])) {
+                #nested_collects
+                #append_values
+            }
+        }
+    }
+}
+
+/// Derive from the given fields. Return false if the fields is a Unit,
+/// true otherwise.
+fn derive_struct_fields<'a>(
+    fields: &'a Fields,
+    types: &mut Vec<&'a Type>,
+    values: &mut Vec<String>,
+) -> bool {
+    let fields = match *fields {
+        Fields::Unit => return false,
+        Fields::Named(ref fields) => fields.named.iter(),
+        Fields::Unnamed(ref fields) => fields.unnamed.iter(),
+    };
+    types.extend(fields.filter_map(|field| {
+        let info_attrs = cg::parse_field_attrs::<ValueInfoFieldAttrs>(field);
+        if let Some(other_values) = info_attrs.other_values {
+            for value in other_values.split(",") {
+                values.push(value.to_string());
+            }
+        }
+        if info_attrs.represents_keyword {
+            let ident = field.ident.as_ref()
+                .expect("only named field should use represents_keyword");
+            values.push(cg::to_css_identifier(ident.as_ref()));
+            return None;
+        }
+        let css_attrs = cg::parse_field_attrs::<CssFieldAttrs>(field);
+        if let Some(if_empty) = css_attrs.if_empty {
+            values.push(if_empty);
+        }
+        if !css_attrs.skip {
+            Some(&field.ty)
+        } else {
+            None
+        }
+    }));
+    true
+}
+
+#[darling(attributes(value_info), default)]
+#[derive(Default, FromDeriveInput)]
+struct ValueInfoInputAttrs {
+    ty: Option<Ident>,
+    other_values: Option<String>,
+}
+
+#[darling(attributes(value_info), default)]
+#[derive(Default, FromVariant)]
+struct ValueInfoVariantAttrs {
+    starts_with_keyword: bool,
+    other_values: Option<String>,
+}
+
+#[darling(attributes(value_info), default)]
+#[derive(Default, FromField)]
+struct ValueInfoFieldAttrs {
+    represents_keyword: bool,
+    other_values: Option<String>,
+}
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..722107da0cd 100644
--- a/components/style_derive/to_css.rs
+++ b/components/style_derive/to_css.rs
@@ -75,9 +75,12 @@ 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.skip {
+        return quote!(Ok(()));
+    }
     if variant_attrs.dimension {
         assert_eq!(bindings.len(), 1);
         assert!(
@@ -207,12 +210,12 @@ 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)]
@@ -223,14 +226,15 @@ pub struct CssVariantAttrs {
     pub dimension: bool,
     pub keyword: Option<String>,
     pub aliases: Option<String>,
+    pub skip: bool,
 }
 
 #[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/Cargo.toml b/components/style_traits/Cargo.toml
index a2fafc6e978..67a6c851dce 100644
--- a/components/style_traits/Cargo.toml
+++ b/components/style_traits/Cargo.toml
@@ -10,7 +10,7 @@ name = "style_traits"
 path = "lib.rs"
 
 [features]
-servo = ["serde", "servo_atoms", "cssparser/serde", "webrender_api"]
+servo = ["serde", "servo_atoms", "cssparser/serde", "webrender_api", "servo_url"]
 gecko = []
 
 [dependencies]
@@ -24,4 +24,5 @@ selectors = { path = "../selectors" }
 serde = {version = "1.0", optional = true}
 webrender_api = {git = "https://github.com/servo/webrender", optional = true}
 servo_atoms = {path = "../atoms", optional = true}
-servo_arc = {path = "../servo_arc" }
+servo_arc = { path = "../servo_arc" }
+servo_url = { path = "../url", optional = true }
diff --git a/components/style_traits/cursor.rs b/components/style_traits/cursor.rs
index 3ffd2814382..c8d410ce23b 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, KeywordsCollectFn, SpecifiedValueInfo, ToCss};
 
 macro_rules! define_cursor {
     (
@@ -57,6 +57,15 @@ macro_rules! define_cursor {
                 }
             }
         }
+
+        impl SpecifiedValueInfo for CursorKind {
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                f(&[
+                    $($c_css,)+
+                    $($g_css,)+
+                ]);
+            }
+        }
     }
 }
 
diff --git a/components/style_traits/lib.rs b/components/style_traits/lib.rs
index 3b7304b1aa7..f232b157cf9 100644
--- a/components/style_traits/lib.rs
+++ b/components/style_traits/lib.rs
@@ -22,6 +22,7 @@ extern crate selectors;
 #[cfg(feature = "servo")] extern crate webrender_api;
 extern crate servo_arc;
 #[cfg(feature = "servo")] extern crate servo_atoms;
+#[cfg(feature = "servo")] extern crate servo_url;
 
 #[cfg(feature = "servo")] pub use webrender_api::DevicePixel;
 
@@ -73,11 +74,13 @@ 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, KeywordsCollectFn, 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..28e1eef25e6
--- /dev/null
+++ b/components/style_traits/specified_value_info.rs
@@ -0,0 +1,134 @@
+/* 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;
+use std::sync::Arc as StdArc;
+
+/// 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;
+}
+
+/// See SpecifiedValueInfo::collect_completion_keywords.
+pub type KeywordsCollectFn<'a> = &'a mut FnMut(&[&'static str]);
+
+/// Information of values of a given specified value type.
+///
+/// This trait is derivable with `#[derive(SpecifiedValueInfo)]`.
+///
+/// The algorithm traverses the type definition. For `SUPPORTED_TYPES`,
+/// it puts an or'ed value of `SUPPORTED_TYPES` of all types it finds.
+/// For `collect_completion_keywords`, it recursively invokes this
+/// method on types found, and lists all keyword values and function
+/// names following the same rule as `ToCss` in that method.
+///
+/// Some attributes of `ToCss` can affect the behavior, specifically:
+/// * If `#[css(function)]` is found, the content inside the annotated
+///   variant (or the whole type) isn't traversed, only the function
+///   name is listed in `collect_completion_keywords`.
+/// * If `#[css(skip)]` is found, the content inside the variant or
+///   field is ignored.
+/// * Values listed in `#[css(if_empty)]`, `#[css(aliases)]`, and
+///   `#[css(keyword)]` are added into `collect_completion_keywords`.
+///
+/// In addition to `css` attributes, it also has `value_info` helper
+/// attributes, including:
+/// * `#[value_info(ty = "TYPE")]` can be used to specify a constant
+///   from `CssType` to `SUPPORTED_TYPES`.
+/// * `#[value_info(other_values = "value1,value2")]` can be used to
+///   add other values related to a field, variant, or the type itself
+///   into `collect_completion_keywords`.
+/// * `#[value_info(starts_with_keyword)]` can be used on variants to
+///   add the name of a non-unit variant (serialized like `ToCss`) into
+///   `collect_completion_keywords`.
+/// * `#[value_info(represents_keyword)]` can be used on fields into
+///   `collect_completion_keywords`.
+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;
+
+    /// Collect value starting words for the given specified value type.
+    /// This includes keyword and function names which can appear at the
+    /// beginning of a value of this type.
+    ///
+    /// Caller should pass in a callback function to accept the list of
+    /// values. The callback function can be called multiple times, and
+    /// some values passed to the callback may be duplicate.
+    fn collect_completion_keywords(_f: KeywordsCollectFn) {}
+}
+
+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 {}
+
+#[cfg(feature = "servo")]
+impl SpecifiedValueInfo for ::servo_atoms::Atom {}
+#[cfg(feature = "servo")]
+impl SpecifiedValueInfo for ::servo_url::ServoUrl {}
+
+impl<T: SpecifiedValueInfo + ?Sized> SpecifiedValueInfo for Box<T> {
+    const SUPPORTED_TYPES: u8 = T::SUPPORTED_TYPES;
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        T::collect_completion_keywords(f);
+    }
+}
+
+impl<T: SpecifiedValueInfo> SpecifiedValueInfo for [T] {
+    const SUPPORTED_TYPES: u8 = T::SUPPORTED_TYPES;
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        T::collect_completion_keywords(f);
+    }
+}
+
+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;
+            fn collect_completion_keywords(f: KeywordsCollectFn) {
+                $param::collect_completion_keywords(f);
+            }
+        }
+    }
+}
+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!(StdArc<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;
+
+    fn collect_completion_keywords(f: KeywordsCollectFn) {
+        T1::collect_completion_keywords(f);
+        T2::collect_completion_keywords(f);
+    }
+}
diff --git a/components/style_traits/values.rs b/components/style_traits/values.rs
index d6bd05b7b40..481eb1aff6d 100644
--- a/components/style_traits/values.rs
+++ b/components/style_traits/values.rs
@@ -173,16 +173,10 @@ where
         Self { inner, separator }
     }
 
-    /// Serialises a CSS value, writing any separator as necessary.
-    ///
-    /// The separator is never written before any `item` produces any output,
-    /// and is written in subsequent calls only if the `item` produces some
-    /// output on its own again. This lets us handle `Option<T>` fields by
-    /// just not printing anything on `None`.
     #[inline]
-    pub fn item<T>(&mut self, item: &T) -> fmt::Result
+    fn write_item<F>(&mut self, f: F) -> fmt::Result
     where
-        T: ToCss,
+        F: FnOnce(&mut CssWriter<'b, W>) -> fmt::Result
     {
         let old_prefix = self.inner.prefix;
         if old_prefix.is_none() {
@@ -191,7 +185,7 @@ where
             // to write the separator next time we produce output again.
             self.inner.prefix = Some(self.separator);
         }
-        item.to_css(&mut self.inner)?;
+        f(self.inner)?;
         match (old_prefix, self.inner.prefix) {
             (_, None) => {
                 // This call produced output and cleaned up after itself.
@@ -213,6 +207,29 @@ where
         }
         Ok(())
     }
+
+    /// Serialises a CSS value, writing any separator as necessary.
+    ///
+    /// The separator is never written before any `item` produces any output,
+    /// and is written in subsequent calls only if the `item` produces some
+    /// output on its own again. This lets us handle `Option<T>` fields by
+    /// just not printing anything on `None`.
+    #[inline]
+    pub fn item<T>(&mut self, item: &T) -> fmt::Result
+    where
+        T: ToCss,
+    {
+        self.write_item(|inner| item.to_css(inner))
+    }
+
+    /// Writes a string as-is (i.e. not escaped or wrapped in quotes)
+    /// with any separator as necessary.
+    ///
+    /// See SequenceWriter::item.
+    #[inline]
+    pub fn raw_item(&mut self, item: &str) -> fmt::Result {
+        self.write_item(|inner| inner.write_str(item))
+    }
 }
 
 /// A wrapper type that implements `ToCss` by printing its inner field.
diff --git a/ports/geckolib/Cargo.toml b/ports/geckolib/Cargo.toml
index a22080ce1c8..8703128ab03 100644
--- a/ports/geckolib/Cargo.toml
+++ b/ports/geckolib/Cargo.toml
@@ -17,7 +17,6 @@ gecko_debug = ["style/gecko_debug"]
 atomic_refcell = "0.1"
 cssparser = "0.23.0"
 cstr = "0.1.2"
-env_logger = {version = "0.5", default-features = false} # disable `regex` to reduce code size
 libc = "0.2"
 log = {version = "0.4", features = ["release_max_level_info"]}
 malloc_size_of = {path = "../../components/malloc_size_of"}
diff --git a/ports/geckolib/glue.rs b/ports/geckolib/glue.rs
index 04d5a22cd40..e602401c954 100644
--- a/ports/geckolib/glue.rs
+++ b/ports/geckolib/glue.rs
@@ -4,15 +4,14 @@
 
 use cssparser::{ParseErrorKind, Parser, ParserInput, SourceLocation};
 use cssparser::ToCss as ParserToCss;
-use env_logger::Builder;
 use malloc_size_of::MallocSizeOfOps;
-use nsstring::nsCString;
+use nsstring::{nsCString, nsStringRepr};
 use selectors::{NthIndexCache, SelectorList};
 use selectors::matching::{MatchingContext, MatchingMode, matches_selector};
 use servo_arc::{Arc, ArcBorrow, RawOffsetArc};
 use smallvec::SmallVec;
 use std::cell::RefCell;
-use std::env;
+use std::collections::BTreeSet;
 use std::fmt::Write;
 use std::iter;
 use std::mem;
@@ -137,7 +136,7 @@ use style::properties::{parse_one_declaration_into, parse_style_attribute};
 use style::properties::animated_properties::AnimationValue;
 use style::properties::animated_properties::compare_property_priority;
 use style::rule_cache::RuleCacheConditions;
-use style::rule_tree::{CascadeLevel, StrongRuleNode, StyleSource};
+use style::rule_tree::{CascadeLevel, StrongRuleNode};
 use style::selector_parser::{PseudoElementCascadeType, SelectorImpl};
 use style::shared_lock::{SharedRwLockReadGuard, StylesheetGuards, ToCssWithGuard, Locked};
 use style::string_cache::{Atom, WeakAtom};
@@ -164,7 +163,7 @@ use style::values::generics::rect::Rect;
 use style::values::specified;
 use style::values::specified::gecko::{IntersectionObserverRootMargin, PixelOrPercentage};
 use style::values::specified::source_size_list::SourceSizeList;
-use style_traits::{CssWriter, ParsingMode, StyleParseErrorKind, ToCss};
+use style_traits::{CssType, CssWriter, ParsingMode, StyleParseErrorKind, ToCss};
 use super::error_reporter::ErrorReporter;
 use super::stylesheet_loader::{AsyncStylesheetParser, StylesheetLoader};
 
@@ -184,14 +183,6 @@ static mut DUMMY_URL_DATA: *mut URLExtraData = 0 as *mut URLExtraData;
 pub extern "C" fn Servo_Initialize(dummy_url_data: *mut URLExtraData) {
     use style::gecko_bindings::sugar::origin_flags;
 
-    // Initialize logging.
-    let mut builder = Builder::new();
-    let default_level = if cfg!(debug_assertions) { "warn" } else { "error" };
-    match env::var("RUST_LOG") {
-      Ok(v) => builder.parse(&v).init(),
-      _ => builder.parse(default_level).init(),
-    };
-
     // Pretend that we're a Servo Layout thread, to make some assertions happy.
     thread_state::initialize(thread_state::ThreadState::LAYOUT);
 
@@ -938,20 +929,36 @@ pub extern "C" fn Servo_ComputedValues_ExtractAnimationValue(
     }
 }
 
+macro_rules! parse_enabled_property_name {
+    ($prop_name:ident, $found:ident, $default:expr) => {{
+        let prop_name = $prop_name.as_ref().unwrap().as_str_unchecked();
+        // XXX This can be simplified once Option::filter is stable.
+        let prop_id = PropertyId::parse(prop_name).ok().and_then(|p| {
+            if p.enabled_for_all_content() {
+                Some(p)
+            } else {
+                None
+            }
+        });
+        match prop_id {
+            Some(p) => {
+                *$found = true;
+                p
+            }
+            None => {
+                *$found = false;
+                return $default;
+            }
+        }
+    }}
+}
+
 #[no_mangle]
 pub unsafe extern "C" fn Servo_Property_IsShorthand(
     prop_name: *const nsACString,
     found: *mut bool
 ) -> bool {
-    let prop_id = PropertyId::parse(prop_name.as_ref().unwrap().as_str_unchecked());
-    let prop_id = match prop_id {
-        Ok(ref p) if p.enabled_for_all_content() => p,
-        _ => {
-            *found = false;
-            return false;
-        }
-    };
-    *found = true;
+    let prop_id = parse_enabled_property_name!(prop_name, found, false);
     prop_id.is_shorthand()
 }
 
@@ -974,6 +981,53 @@ pub unsafe extern "C" fn Servo_Property_IsInherited(
     longhand_id.inherited()
 }
 
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_SupportsType(
+    prop_name: *const nsACString,
+    ty: u32,
+    found: *mut bool,
+) -> bool {
+    let prop_id = parse_enabled_property_name!(prop_name, found, false);
+    // This should match the constants in InspectorUtils.
+    // (Let's don't bother importing InspectorUtilsBinding into bindings
+    // because it is not used anywhere else, and issue here would be
+    // caught by the property-db test anyway.)
+    let ty = match ty {
+        1 => CssType::COLOR,
+        2 => CssType::GRADIENT,
+        3 => CssType::TIMING_FUNCTION,
+        _ => unreachable!("unknown CSS type {}", ty),
+    };
+    prop_id.supports_type(ty)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn Servo_Property_GetCSSValuesForProperty(
+    prop_name: *const nsACString,
+    found: *mut bool,
+    result: *mut nsTArray<nsStringRepr>,
+) {
+    let prop_id = parse_enabled_property_name!(prop_name, found, ());
+    // Use B-tree set for unique and sorted result.
+    let mut values = BTreeSet::<&'static str>::new();
+    prop_id.collect_property_completion_keywords(&mut |list| values.extend(list.iter()));
+
+    let mut extras = vec![];
+    if values.contains("transparent") {
+        // This is a special value devtools use to avoid inserting the
+        // long list of color keywords. We need to prepend it to values.
+        extras.push("COLOR");
+    }
+
+    let result = result.as_mut().unwrap();
+    let len = extras.len() + values.len();
+    bindings::Gecko_ResizeTArrayForStrings(result, len as u32);
+
+    for (src, dest) in extras.iter().chain(values.iter()).zip(result.iter_mut()) {
+        dest.write_str(src).unwrap();
+    }
+}
+
 #[no_mangle]
 pub extern "C" fn Servo_Property_IsAnimatable(property: nsCSSPropertyID) -> bool {
     use style::properties::animated_properties;
@@ -3123,8 +3177,8 @@ pub extern "C" fn Servo_ComputedValues_GetStyleRuleList(
 
     let mut result = SmallVec::<[_; 10]>::new();
     for node in rule_node.self_and_ancestors() {
-        let style_rule = match *node.style_source() {
-            StyleSource::Style(ref rule) => rule,
+        let style_rule = match node.style_source().and_then(|x| x.as_rule()) {
+            Some(rule) => rule,
             _ => continue,
         };
 
@@ -3141,9 +3195,11 @@ pub extern "C" fn Servo_ComputedValues_GetStyleRuleList(
 
     unsafe { rules.set_len(result.len() as u32) };
     for (ref src, ref mut dest) in result.into_iter().zip(rules.iter_mut()) {
-        src.with_raw_offset_arc(|arc| {
-            **dest = *Locked::<StyleRule>::arc_as_borrowed(arc);
-        })
+        src.with_arc(|a| {
+            a.with_raw_offset_arc(|arc| {
+                **dest = *Locked::<StyleRule>::arc_as_borrowed(arc);
+            })
+        });
     }
 }
 
diff --git a/ports/geckolib/lib.rs b/ports/geckolib/lib.rs
index d48a096df64..79150f62bf7 100644
--- a/ports/geckolib/lib.rs
+++ b/ports/geckolib/lib.rs
@@ -5,7 +5,6 @@
 
 extern crate cssparser;
 #[macro_use] extern crate cstr;
-extern crate env_logger;
 extern crate libc;
 #[macro_use] extern crate log;
 extern crate malloc_size_of;
diff --git a/ports/geckolib/tests/build.rs b/ports/geckolib/tests/build.rs
index 7feb9d10405..8de7326b574 100644
--- a/ports/geckolib/tests/build.rs
+++ b/ports/geckolib/tests/build.rs
@@ -49,7 +49,16 @@ fn main() {
                 // Which is not a problem, but would cause this to not compile.
                 //
                 // Skip this until libclang is updated there.
-                if &cap[1] == "InvalidateStyleForDocStateChanges" {
+                //
+                // Also skip Servo_Element_IsDisplayContents because we
+                // forward-declare it in Element.h without the type bindgen uses
+                // to replace it by a reference, and it depends on the include
+                // order in ServoBindings.h. We have the same problem for
+                // ComputedStyle_{AddRef / Release}, we just don't hit it
+                // because they're included later...
+                if &cap[1] == "InvalidateStyleForDocStateChanges" ||
+                    &cap[1] == "Element_IsDisplayContents"
+                {
                     continue;
                 }
                 w.write_all(format!("    [ Servo_{0}, bindings::Servo_{0} ];\n", &cap[1]).as_bytes()).unwrap();
diff --git a/ports/geckolib/tests/lib.rs b/ports/geckolib/tests/lib.rs
index 6fc2b36029c..9981611d17a 100644
--- a/ports/geckolib/tests/lib.rs
+++ b/ports/geckolib/tests/lib.rs
@@ -14,7 +14,6 @@
 extern crate atomic_refcell;
 extern crate cssparser;
 #[macro_use] extern crate cstr;
-extern crate env_logger;
 extern crate geckoservo;
 #[macro_use] extern crate log;
 extern crate malloc_size_of;
diff --git a/ports/geckolib/tests/size_of.rs b/ports/geckolib/tests/size_of.rs
index 9691c4cd385..8905650dc2a 100644
--- a/ports/geckolib/tests/size_of.rs
+++ b/ports/geckolib/tests/size_of.rs
@@ -35,8 +35,8 @@ size_of_test!(test_size_of_element_data, ElementData, 24);
 
 size_of_test!(test_size_of_property_declaration, style::properties::PropertyDeclaration, 32);
 
-size_of_test!(test_size_of_application_declaration_block, ApplicableDeclarationBlock, 24);
-size_of_test!(test_size_of_rule_node, RuleNode, 80);
+size_of_test!(test_size_of_application_declaration_block, ApplicableDeclarationBlock, 16);
+size_of_test!(test_size_of_rule_node, RuleNode, 72);
 
 // This is huge, but we allocate it on the stack and then never move it,
 // we only pass `&mut SourcePropertyDeclaration` references around.
diff --git a/tests/unit/style/properties/serialization.rs b/tests/unit/style/properties/serialization.rs
index 369100aa686..e274d8a2a6a 100644
--- a/tests/unit/style/properties/serialization.rs
+++ b/tests/unit/style/properties/serialization.rs
@@ -487,42 +487,6 @@ mod shorthand_serialization {
         }
     }
 
-    mod outline {
-        use style::values::specified::outline::OutlineStyle;
-        use super::*;
-
-        #[test]
-        fn outline_should_show_all_properties_when_set() {
-            let mut properties = Vec::new();
-
-            let width = BorderSideWidth::Length(Length::from_px(4f32));
-            let style = OutlineStyle::Other(BorderStyle::Solid);
-            let color = RGBA::new(255, 0, 0, 255).into();
-
-            properties.push(PropertyDeclaration::OutlineWidth(width));
-            properties.push(PropertyDeclaration::OutlineStyle(style));
-            properties.push(PropertyDeclaration::OutlineColor(color));
-
-            let serialization = shorthand_properties_to_string(properties);
-            assert_eq!(serialization, "outline: 4px solid rgb(255, 0, 0);");
-        }
-
-        #[test]
-        fn outline_should_serialize_correctly_when_style_is_auto() {
-            let mut properties = Vec::new();
-
-            let width = BorderSideWidth::Length(Length::from_px(4f32));
-            let style = OutlineStyle::Auto;
-            let color = RGBA::new(255, 0, 0, 255).into();
-            properties.push(PropertyDeclaration::OutlineWidth(width));
-            properties.push(PropertyDeclaration::OutlineStyle(style));
-            properties.push(PropertyDeclaration::OutlineColor(color));
-
-            let serialization = shorthand_properties_to_string(properties);
-            assert_eq!(serialization, "outline: 4px auto rgb(255, 0, 0);");
-        }
-    }
-
     mod background {
         use super::*;
 
diff --git a/tests/unit/style/rule_tree/bench.rs b/tests/unit/style/rule_tree/bench.rs
index edc3b70daf4..54af9d39532 100644
--- a/tests/unit/style/rule_tree/bench.rs
+++ b/tests/unit/style/rule_tree/bench.rs
@@ -62,11 +62,12 @@ fn parse_rules(css: &str) -> Vec<(StyleSource, CascadeLevel)> {
     let rules = s.contents.rules.read_with(&guard);
     rules.0.iter().filter_map(|rule| {
         match *rule {
-            CssRule::Style(ref style_rule) => Some(style_rule),
+            CssRule::Style(ref style_rule) => Some((
+                StyleSource::from_rule(style_rule.clone()),
+                CascadeLevel::UserNormal,
+            )),
             _ => None,
         }
-    }).cloned().map(StyleSource::Style).map(|s| {
-        (s, CascadeLevel::UserNormal)
     }).collect()
 }
 
@@ -78,7 +79,7 @@ fn test_insertion_style_attribute(rule_tree: &RuleTree, rules: &[(StyleSource, C
                                   shared_lock: &SharedRwLock)
                                   -> StrongRuleNode {
     let mut rules = rules.to_vec();
-    rules.push((StyleSource::Declarations(Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
+    rules.push((StyleSource::from_declarations(Arc::new(shared_lock.wrap(PropertyDeclarationBlock::with_one(
         PropertyDeclaration::Display(
             longhands::display::SpecifiedValue::Block),
         Importance::Normal
diff --git a/tests/wpt/metadata/css/cssom/shorthand-values.html.ini b/tests/wpt/metadata/css/cssom/shorthand-values.html.ini
index cb0502d1dcd..e0b5a48bdb5 100644
--- a/tests/wpt/metadata/css/cssom/shorthand-values.html.ini
+++ b/tests/wpt/metadata/css/cssom/shorthand-values.html.ini
@@ -26,9 +26,6 @@
   [The serialization of border: solid; border-style: dotted should be canonical.]
     expected: FAIL
 
-  [The serialization of outline-width: 2px; outline-style: dotted; outline-color: blue; should be canonical.]
-    expected: FAIL
-
   [The serialization of list-style-type: circle; list-style-position: inside; list-style-image: initial; should be canonical.]
     expected: FAIL