diff --git a/components/style/properties/data.py b/components/style/properties/data.py
index cdf4560783b..9ee8c08cf18 100644
--- a/components/style/properties/data.py
+++ b/components/style/properties/data.py
@@ -84,12 +84,15 @@ def arg_to_bool(arg):
 
 
 class Longhand(object):
-    def __init__(self, style_struct, name, animatable=None, derived_from=None, keyword=None,
+    def __init__(self, style_struct, name, spec=None, animatable=None, derived_from=None, keyword=None,
                  predefined_type=None, custom_cascade=False, experimental=False, internal=False,
                  need_clone=False, need_index=False, gecko_ffi_name=None, depend_on_viewport_size=False,
                  allowed_in_keyframe_block=True, complex_color=False, cast_type='u8',
                  has_uncacheable_values=False, logical=False):
         self.name = name
+        if not spec:
+            raise TypeError("Spec should be specified for %s" % name)
+        self.spec = spec
         self.keyword = keyword
         self.predefined_type = predefined_type
         self.ident = to_rust_ident(name)
@@ -130,9 +133,12 @@ class Longhand(object):
 
 
 class Shorthand(object):
-    def __init__(self, name, sub_properties, experimental=False, internal=False,
+    def __init__(self, name, sub_properties, spec=None, experimental=False, internal=False,
                  allowed_in_keyframe_block=True):
         self.name = name
+        if not spec:
+            raise TypeError("Spec should be specified for %s" % name)
+        self.spec = spec
         self.ident = to_rust_ident(name)
         self.camel_case = to_camel_case(self.ident)
         self.derived_from = None
diff --git a/components/style/properties/helpers.mako.rs b/components/style/properties/helpers.mako.rs
index e1fac491910..89e9d1d2b2e 100644
--- a/components/style/properties/helpers.mako.rs
+++ b/components/style/properties/helpers.mako.rs
@@ -185,6 +185,7 @@
         if property is None:
             return ""
     %>
+    /// ${property.spec}
     pub mod ${property.ident} {
         #![allow(unused_imports)]
         % if not property.derived_from:
@@ -337,7 +338,7 @@
     </%call>
 </%def>
 
-<%def name="single_keyword_computed(name, values, vector=False, **kwargs)">
+<%def name="single_keyword_computed(name, values, vector=False, extra_specified=None, **kwargs)">
     <%
         keyword_kwargs = {a: kwargs.pop(a, None) for a in [
             'gecko_constant_prefix', 'gecko_enum_prefix',
@@ -347,7 +348,16 @@
     %>
 
     <%def name="inner_body()">
-        pub use self::computed_value::T as SpecifiedValue;
+        % if extra_specified:
+            use style_traits::ToCss;
+            define_css_keyword_enum! { SpecifiedValue:
+                % for value in data.longhands_by_name[name].keyword.values_for(product) + extra_specified.split():
+                    "${value}" => ${to_rust_ident(value)},
+                % endfor
+            }
+        % else:
+            pub use self::computed_value::T as SpecifiedValue;
+        % endif
         pub mod computed_value {
             use style_traits::ToCss;
             define_css_keyword_enum! { T:
@@ -362,12 +372,12 @@
         }
         #[inline]
         pub fn get_initial_specified_value() -> SpecifiedValue {
-            get_initial_value()
+            SpecifiedValue::${to_rust_ident(values.split()[0])}
         }
         #[inline]
         pub fn parse(_context: &ParserContext, input: &mut Parser)
                      -> Result<SpecifiedValue, ()> {
-            computed_value::T::parse(input)
+            SpecifiedValue::parse(input)
         }
     </%def>
     % if vector:
@@ -389,6 +399,7 @@
                                        **kwargs)
 %>
     % if shorthand:
+    /// ${shorthand.spec}
     pub mod ${shorthand.ident} {
         #[allow(unused_imports)]
         use cssparser::Parser;
@@ -540,10 +551,9 @@
     % endif
 </%def>
 
-<%def name="four_sides_shorthand(name, sub_property_pattern, parser_function, needs_context=True)">
-    <%self:shorthand name="${name}" sub_properties="${
-            ' '.join(sub_property_pattern % side
-                     for side in ['top', 'right', 'bottom', 'left'])}">
+<%def name="four_sides_shorthand(name, sub_property_pattern, parser_function, needs_context=True, **kwargs)">
+    <% sub_properties=' '.join(sub_property_pattern % side for side in ['top', 'right', 'bottom', 'left']) %>
+    <%call expr="self.shorthand(name, sub_properties=sub_properties, **kwargs)">
         #[allow(unused_imports)]
         use parser::Parse;
         use super::parse_four_sides;
@@ -575,7 +585,7 @@
                 )
             }
         }
-    </%self:shorthand>
+    </%call>
 </%def>
 
 <%def name="logical_setter_helper(name)">
diff --git a/components/style/properties/longhand/background.mako.rs b/components/style/properties/longhand/background.mako.rs
index ad5562226ce..35420469f56 100644
--- a/components/style/properties/longhand/background.mako.rs
+++ b/components/style/properties/longhand/background.mako.rs
@@ -8,9 +8,11 @@
 
 ${helpers.predefined_type("background-color", "CSSColor",
     "::cssparser::Color::RGBA(::cssparser::RGBA { red: 0., green: 0., blue: 0., alpha: 0. }) /* transparent */",
+    spec="https://drafts.csswg.org/css-backgrounds/#background-color",
     animatable=True, complex_color=True)}
 
 <%helpers:vector_longhand name="background-image" animatable="False"
+                          spec="https://drafts.csswg.org/css-backgrounds/#the-background-image"
                           has_uncacheable_values="${product == 'gecko'}">
     use std::fmt;
     use style_traits::ToCss;
@@ -86,7 +88,8 @@ ${helpers.predefined_type("background-color", "CSSColor",
     }
 </%helpers:vector_longhand>
 
-<%helpers:vector_longhand name="background-position-x" animatable="True">
+<%helpers:vector_longhand name="background-position-x" animatable="True"
+                          spec="https://drafts.csswg.org/css-backgrounds-4/#propdef-background-position-x">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -135,7 +138,8 @@ ${helpers.predefined_type("background-color", "CSSColor",
     }
 </%helpers:vector_longhand>
 
-<%helpers:vector_longhand name="background-position-y" animatable="True">
+<%helpers:vector_longhand name="background-position-y" animatable="True"
+                          spec="https://drafts.csswg.org/css-backgrounds-4/#propdef-background-position-y">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -188,24 +192,29 @@ ${helpers.predefined_type("background-color", "CSSColor",
 ${helpers.single_keyword("background-repeat",
                          "repeat repeat-x repeat-y space round no-repeat",
                          vector=True,
+                         spec="https://drafts.csswg.org/css-backgrounds/#the-background-repeat",
                          animatable=False)}
 
 ${helpers.single_keyword("background-attachment",
                          "scroll fixed" + (" local" if product == "gecko" else ""),
                          vector=True,
+                         spec="https://drafts.csswg.org/css-backgrounds/#the-background-attachment",
                          animatable=False)}
 
 ${helpers.single_keyword("background-clip",
                          "border-box padding-box content-box",
                          vector=True,
+                         spec="https://drafts.csswg.org/css-backgrounds/#the-background-clip",
                          animatable=False)}
 
 ${helpers.single_keyword("background-origin",
                          "padding-box border-box content-box",
                          vector=True,
+                         spec="https://drafts.csswg.org/css-backgrounds/#the-background-origin",
                          animatable=False)}
 
-<%helpers:vector_longhand name="background-size" animatable="True">
+<%helpers:vector_longhand name="background-size" animatable="True"
+                          spec="https://drafts.csswg.org/css-backgrounds/#the-background-size">
     use cssparser::Token;
     use std::ascii::AsciiExt;
     use std::fmt;
@@ -406,4 +415,5 @@ ${helpers.single_keyword("background-blend-mode",
                          """normal multiply screen overlay darken lighten color-dodge
                             color-burn hard-light soft-light difference exclusion hue
                             saturation color luminosity""",
-                         vector="true", products="gecko", animatable=False)}
+                         vector="true", products="gecko", animatable=False,
+                         spec="https://drafts.fxtf.org/compositing/#background-blend-mode")}
diff --git a/components/style/properties/longhand/border.mako.rs b/components/style/properties/longhand/border.mako.rs
index 0393064d532..0da25f2a26b 100644
--- a/components/style/properties/longhand/border.mako.rs
+++ b/components/style/properties/longhand/border.mako.rs
@@ -8,10 +8,17 @@
 <% data.new_style_struct("Border", inherited=False,
                    additional_methods=[Method("border_" + side + "_has_nonzero_width",
                                               "bool") for side in ["top", "right", "bottom", "left"]]) %>
-
+<%
+    def maybe_logical_spec(side, kind):
+        if side[1]: # if it is logical
+            return "https://drafts.csswg.org/css-logical-props/#propdef-border-%s-%s" % (side[0], kind)
+        else:
+            return "https://drafts.csswg.org/css-backgrounds/#border-%s-%s" % (side[0], kind)
+%>
 % for side in ALL_SIDES:
     ${helpers.predefined_type("border-%s-color" % side[0], "CSSColor",
                               "::cssparser::Color::CurrentColor",
+                              spec=maybe_logical_spec(side, "color"),
                               animatable=True, logical = side[1])}
 % endfor
 
@@ -19,11 +26,13 @@
     ${helpers.predefined_type("border-%s-style" % side[0], "BorderStyle",
                               "specified::BorderStyle::none",
                               needs_context=False, need_clone=True,
+                              spec=maybe_logical_spec(side, "style"),
                               animatable=False, logical = side[1])}
 % endfor
 
 % for side in ALL_SIDES:
-    <%helpers:longhand name="border-${side[0]}-width" animatable="True" logical="${side[1]}">
+    <%helpers:longhand name="border-${side[0]}-width" animatable="True" logical="${side[1]}"
+                       spec="${maybe_logical_spec(side, 'width')}">
         use app_units::Au;
         use std::fmt;
         use style_traits::ToCss;
@@ -53,12 +62,14 @@
     ${helpers.predefined_type("border-" + corner + "-radius", "BorderRadiusSize",
                               "computed::BorderRadiusSize::zero()",
                               "parse",
+                              spec="https://drafts.csswg.org/css-backgrounds/#border-%s-radius" % corner,
                               animatable=True)}
 % endfor
 
 ${helpers.single_keyword("box-decoration-break", "slice clone",
                          gecko_enum_prefix="StyleBoxDecorationBreak",
                          gecko_inexhaustive=True,
+                         spec="https://drafts.csswg.org/css-break/#propdef-box-decoration-break",
                          products="gecko", animatable=False)}
 
 ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
@@ -66,10 +77,11 @@ ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
                          gecko_enum_prefix="StyleFloatEdge",
                          gecko_inexhaustive=True,
                          products="gecko",
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-float-edge)",
                          animatable=False)}
 
-// https://drafts.csswg.org/css-backgrounds-3/#border-image-source
-<%helpers:longhand name="border-image-source" products="gecko" animatable="False">
+<%helpers:longhand name="border-image-source" products="gecko" animatable="False"
+                   spec="https://drafts.csswg.org/css-backgrounds/#border-image-source">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -144,8 +156,8 @@ ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
     }
 </%helpers:longhand>
 
-// https://drafts.csswg.org/css-backgrounds-3/#border-image-outset
-<%helpers:longhand name="border-image-outset" products="gecko" animatable="False">
+<%helpers:longhand name="border-image-outset" products="gecko" animatable="False"
+                   spec="https://drafts.csswg.org/css-backgrounds/#border-image-outset">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -260,8 +272,8 @@ ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
     }
 </%helpers:longhand>
 
-// https://drafts.csswg.org/css-backgrounds-3/#border-image-repeat
-<%helpers:longhand name="border-image-repeat" products="gecko" animatable="False">
+<%helpers:longhand name="border-image-repeat" products="gecko" animatable="False"
+                   spec="https://drafts.csswg.org/css-backgrounds/#border-image-repeat">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -338,8 +350,8 @@ ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
     }
 </%helpers:longhand>
 
-// https://drafts.csswg.org/css-backgrounds-3/#border-image-width
-<%helpers:longhand name="border-image-width" products="gecko" animatable="False">
+<%helpers:longhand name="border-image-width" products="gecko" animatable="False"
+                   spec="https://drafts.csswg.org/css-backgrounds/#border-image-width">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -538,8 +550,8 @@ ${helpers.single_keyword("-moz-float-edge", "content-box margin-box",
     }
 </%helpers:longhand>
 
-// https://drafts.csswg.org/css-backgrounds-3/#border-image-slice
-<%helpers:longhand name="border-image-slice" products="gecko" animatable="False">
+<%helpers:longhand name="border-image-slice" products="gecko" animatable="False"
+                   spec="https://drafts.csswg.org/css-backgrounds/#border-image-slice">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
diff --git a/components/style/properties/longhand/box.mako.rs b/components/style/properties/longhand/box.mako.rs
index 3b5cd6bba4c..6819368502e 100644
--- a/components/style/properties/longhand/box.mako.rs
+++ b/components/style/properties/longhand/box.mako.rs
@@ -13,7 +13,8 @@
 <%helpers:longhand name="display"
                    need_clone="True"
                    animatable="False"
-                   custom_cascade="${product == 'servo'}">
+                   custom_cascade="${product == 'servo'}"
+                   spec="https://drafts.csswg.org/css-display/#propdef-display">
     <%
         values = """inline block inline-block
             table inline-table table-row-group table-header-group table-footer-group
@@ -94,15 +95,19 @@
 </%helpers:longhand>
 
 ${helpers.single_keyword("position", "static absolute relative fixed",
-                         need_clone=True, extra_gecko_values="sticky", animatable=False)}
+                         need_clone=True, extra_gecko_values="sticky", animatable=False,
+                         spec="https://drafts.csswg.org/css-position/#position-property")}
 
 <%helpers:single_keyword_computed name="float"
                                   values="none left right"
+                                  // https://drafts.csswg.org/css-logical-props/#float-clear
+                                  extra_specified="inline-start inline-end"
                                   animatable="False"
                                   need_clone="True"
                                   gecko_enum_prefix="StyleFloat"
                                   gecko_inexhaustive="True"
-                                  gecko_ffi_name="mFloat">
+                                  gecko_ffi_name="mFloat"
+                                  spec="https://drafts.csswg.org/css-box/#propdef-float">
     use values::NoViewportPercentage;
     impl NoViewportPercentage for SpecifiedValue {}
     impl ToComputedValue for SpecifiedValue {
@@ -114,27 +119,75 @@ ${helpers.single_keyword("position", "static absolute relative fixed",
                 longhands::position::SpecifiedValue::absolute |
                 longhands::position::SpecifiedValue::fixed);
             if positioned {
-                SpecifiedValue::none
+                computed_value::T::none
             } else {
-                *self
+                let ltr = context.style().writing_mode.is_bidi_ltr();
+                // https://drafts.csswg.org/css-logical-props/#float-clear
+                match *self {
+                    SpecifiedValue::inline_start if ltr => computed_value::T::left,
+                    SpecifiedValue::inline_start => computed_value::T::right,
+                    SpecifiedValue::inline_end if ltr => computed_value::T::right,
+                    SpecifiedValue::inline_end => computed_value::T::left,
+                    % for value in "none left right".split():
+                        SpecifiedValue::${value} => computed_value::T::${value},
+                    % endfor
+                }
             }
         }
         #[inline]
         fn from_computed_value(computed: &computed_value::T) -> SpecifiedValue {
-          *computed
+            match *computed {
+                % for value in "none left right".split():
+                    computed_value::T::${value} => SpecifiedValue::${value},
+                % endfor
+            }
         }
     }
-
 </%helpers:single_keyword_computed>
 
-${helpers.single_keyword("clear", "none left right both",
-                         animatable=False, gecko_ffi_name="mBreakType",
-                         gecko_enum_prefix="StyleClear")}
+<%helpers:single_keyword_computed name="clear"
+                                  values="none left right both"
+                                  // https://drafts.csswg.org/css-logical-props/#float-clear
+                                  extra_specified="inline-start inline-end"
+                                  animatable="False"
+                                  gecko_enum_prefix="StyleClear"
+                                  gecko_ffi_name="mBreakType"
+                                  spec="https://www.w3.org/TR/CSS2/visuren.html#flow-control">
+    use values::NoViewportPercentage;
+    impl NoViewportPercentage for SpecifiedValue {}
+    impl ToComputedValue for SpecifiedValue {
+        type ComputedValue = computed_value::T;
+
+        #[inline]
+        fn to_computed_value(&self, context: &Context) -> computed_value::T {
+            let ltr = context.style().writing_mode.is_bidi_ltr();
+            // https://drafts.csswg.org/css-logical-props/#float-clear
+            match *self {
+                SpecifiedValue::inline_start if ltr => computed_value::T::left,
+                SpecifiedValue::inline_start => computed_value::T::right,
+                SpecifiedValue::inline_end if ltr => computed_value::T::right,
+                SpecifiedValue::inline_end => computed_value::T::left,
+                % for value in "none left right both".split():
+                    SpecifiedValue::${value} => computed_value::T::${value},
+                % endfor
+            }
+        }
+        #[inline]
+        fn from_computed_value(computed: &computed_value::T) -> SpecifiedValue {
+            match *computed {
+                % for value in "none left right both".split():
+                    computed_value::T::${value} => SpecifiedValue::${value},
+                % endfor
+            }
+        }
+    }
+</%helpers:single_keyword_computed>
 
 <%helpers:longhand name="-servo-display-for-hypothetical-box"
                    animatable="False"
                    derived_from="display"
-                   products="servo">
+                   products="servo"
+                   spec="Internal (not web-exposed)">
     pub use super::display::{SpecifiedValue, get_initial_value};
     pub use super::display::{parse};
 
@@ -150,7 +203,8 @@ ${helpers.single_keyword("clear", "none left right both",
 
 </%helpers:longhand>
 
-<%helpers:longhand name="vertical-align" animatable="True">
+<%helpers:longhand name="vertical-align" animatable="True"
+                   spec="https://www.w3.org/TR/CSS2/visudet.html#propdef-vertical-align">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -277,20 +331,25 @@ ${helpers.single_keyword("clear", "none left right both",
 
 // CSS 2.1, Section 11 - Visual effects
 
-// Non-standard, see https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box#Specifications
 ${helpers.single_keyword("-servo-overflow-clip-box", "padding-box content-box",
-                         products="servo", animatable=False, internal=True)}
+    products="servo", animatable=False, internal=True,
+    spec="Internal, not web-exposed, \
+          may be standardized in the future (https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box)")}
 
 ${helpers.single_keyword("overflow-clip-box", "padding-box content-box",
-                         products="gecko", animatable=False, internal=True)}
+    products="gecko", animatable=False, internal=True,
+    spec="Internal, not web-exposed, \
+          may be standardized in the future (https://developer.mozilla.org/en-US/docs/Web/CSS/overflow-clip-box)")}
 
 // FIXME(pcwalton, #2742): Implement scrolling for `scroll` and `auto`.
 ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
                          need_clone=True, animatable=False,
-                         gecko_constant_prefix="NS_STYLE_OVERFLOW")}
+                         gecko_constant_prefix="NS_STYLE_OVERFLOW",
+                         spec="https://drafts.csswg.org/css-overflow/#propdef-overflow-x")}
 
 // FIXME(pcwalton, #2742): Implement scrolling for `scroll` and `auto`.
-<%helpers:longhand name="overflow-y" need_clone="True" animatable="False">
+<%helpers:longhand name="overflow-y" need_clone="True" animatable="False"
+                   spec="https://drafts.csswg.org/css-overflow/#propdef-overflow-y">
     use super::overflow_x;
 
     use std::fmt;
@@ -337,7 +396,8 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 
 <%helpers:longhand name="transition-duration"
                    need_index="True"
-                   animatable="False">
+                   animatable="False"
+                   spec="https://drafts.csswg.org/css-transitions/#propdef-transition-duration">
     use values::computed::ComputedValueAsSpecified;
     use values::specified::Time;
 
@@ -393,7 +453,8 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 // TODO(pcwalton): Lots more timing functions.
 <%helpers:longhand name="transition-timing-function"
                    need_index="True"
-                   animatable="False">
+                   animatable="False"
+                   spec="https://drafts.csswg.org/css-transitions/#propdef-transition-timing-function">
     use self::computed_value::{StartEnd, TransitionTimingFunction};
 
     use euclid::point::{Point2D, TypedPoint2D};
@@ -593,7 +654,8 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 
 <%helpers:longhand name="transition-property"
                    need_index="True"
-                   animatable="False">
+                   animatable="False"
+                   spec="https://drafts.csswg.org/css-transitions/#propdef-transition-property">
 
     use values::computed::ComputedValueAsSpecified;
 
@@ -645,7 +707,8 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 
 <%helpers:longhand name="transition-delay"
                    need_index="True"
-                   animatable="False">
+                   animatable="False"
+                   spec="https://drafts.csswg.org/css-transitions/#propdef-transition-delay">
     pub use properties::longhands::transition_duration::{SingleSpecifiedValue, SpecifiedValue};
     pub use properties::longhands::transition_duration::computed_value;
     pub use properties::longhands::transition_duration::{get_initial_value, get_initial_single_value, parse};
@@ -654,7 +717,8 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 <%helpers:longhand name="animation-name"
                    need_index="True"
                    animatable="False",
-                   allowed_in_keyframe_block="False">
+                   allowed_in_keyframe_block="False"
+                   spec="https://drafts.csswg.org/css-animations/#propdef-animation-name">
     use values::computed::ComputedValueAsSpecified;
     use values::NoViewportPercentage;
 
@@ -730,6 +794,7 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 <%helpers:longhand name="animation-duration"
                    need_index="True"
                    animatable="False",
+                   spec="https://drafts.csswg.org/css-animations/#propdef-animation-duration",
                    allowed_in_keyframe_block="False">
     pub use super::transition_duration::computed_value;
     pub use super::transition_duration::{get_initial_value, get_initial_single_value, parse};
@@ -740,6 +805,7 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 <%helpers:longhand name="animation-timing-function"
                    need_index="True"
                    animatable="False",
+                   spec="https://drafts.csswg.org/css-animations/#propdef-animation-timing-function",
                    allowed_in_keyframe_block="False">
     pub use super::transition_timing_function::computed_value;
     pub use super::transition_timing_function::{get_initial_value, get_initial_single_value, parse};
@@ -750,6 +816,7 @@ ${helpers.single_keyword("overflow-x", "visible hidden scroll auto",
 <%helpers:longhand name="animation-iteration-count"
                    need_index="True"
                    animatable="False",
+                   spec="https://drafts.csswg.org/css-animations/#propdef-animation-iteration-count",
                    allowed_in_keyframe_block="False">
     use values::computed::ComputedValueAsSpecified;
     use values::NoViewportPercentage;
@@ -842,6 +909,7 @@ ${helpers.single_keyword("animation-direction",
                          need_index=True,
                          animatable=False,
                          vector=True,
+                         spec="https://drafts.csswg.org/css-animations/#propdef-animation-direction",
                          allowed_in_keyframe_block=False)}
 
 // animation-play-state is the exception to the rule for allowed_in_keyframe_block:
@@ -852,6 +920,7 @@ ${helpers.single_keyword("animation-play-state",
                          need_index=True,
                          animatable=False,
                          vector=True,
+                         spec="https://drafts.csswg.org/css-animations/#propdef-animation-play-state",
                          allowed_in_keyframe_block=True)}
 
 ${helpers.single_keyword("animation-fill-mode",
@@ -859,11 +928,13 @@ ${helpers.single_keyword("animation-fill-mode",
                          need_index=True,
                          animatable=False,
                          vector=True,
+                         spec="https://drafts.csswg.org/css-animations/#propdef-animation-fill-mode",
                          allowed_in_keyframe_block=False)}
 
 <%helpers:longhand name="animation-delay"
                    need_index="True"
                    animatable="False",
+                   spec="https://drafts.csswg.org/css-animations/#propdef-animation-delay",
                    allowed_in_keyframe_block="False">
     pub use super::transition_duration::computed_value;
     pub use super::transition_duration::{get_initial_value, get_initial_single_value, parse};
@@ -871,7 +942,8 @@ ${helpers.single_keyword("animation-fill-mode",
     pub use super::transition_duration::SingleSpecifiedValue;
 </%helpers:longhand>
 
-<%helpers:longhand products="gecko" name="scroll-snap-points-y" animatable="False">
+<%helpers:longhand products="gecko" name="scroll-snap-points-y" animatable="False"
+                   spec="Nonstandard (https://www.w3.org/TR/2015/WD-css-snappoints-1-20150326/#scroll-snap-points)">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -965,7 +1037,8 @@ ${helpers.single_keyword("animation-fill-mode",
     }
 </%helpers:longhand>
 
-<%helpers:longhand products="gecko" name="scroll-snap-points-x" animatable="False">
+<%helpers:longhand products="gecko" name="scroll-snap-points-x" animatable="False"
+                   spec="Nonstandard (https://www.w3.org/TR/2015/WD-css-snappoints-1-20150326/#scroll-snap-points)">
     pub use super::scroll_snap_points_y::SpecifiedValue;
     pub use super::scroll_snap_points_y::computed_value;
     pub use super::scroll_snap_points_y::get_initial_value;
@@ -974,7 +1047,8 @@ ${helpers.single_keyword("animation-fill-mode",
 
 
 
-<%helpers:longhand name="transform" products="gecko servo" animatable="${product == 'servo'}">
+<%helpers:longhand name="transform" products="gecko servo" animatable="${product == 'servo'}"
+                   spec="https://drafts.csswg.org/css-transforms/#propdef-transform">
     use app_units::Au;
     use style_traits::ToCss;
     use values::CSSFloat;
@@ -1501,17 +1575,18 @@ ${helpers.single_keyword("animation-fill-mode",
 ${helpers.single_keyword("scroll-behavior",
                          "auto smooth",
                          products="gecko",
+                         spec="https://drafts.csswg.org/cssom-view/#propdef-scroll-behavior",
                          animatable=False)}
 
-// Non-standard: https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-type-x
 ${helpers.single_keyword("scroll-snap-type-x",
                          "none mandatory proximity",
                          products="gecko",
                          gecko_constant_prefix="NS_STYLE_SCROLL_SNAP_TYPE",
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-type-x)",
                          animatable=False)}
 
-// Non-standard: https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-type-y
-<%helpers:longhand products="gecko" name="scroll-snap-type-y" animatable="False">
+<%helpers:longhand products="gecko" name="scroll-snap-type-y" animatable="False"
+                   spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/scroll-snap-type-x)">
     pub use super::scroll_snap_type_x::SpecifiedValue;
     pub use super::scroll_snap_type_x::computed_value;
     pub use super::scroll_snap_type_x::get_initial_value;
@@ -1523,41 +1598,48 @@ ${helpers.single_keyword("scroll-snap-type-x",
 ${helpers.single_keyword("isolation",
                          "auto isolate",
                          products="gecko",
+                         spec="https://drafts.fxtf.org/compositing/#isolation",
                          animatable=False)}
 
+// TODO add support for logical values recto and verso
 ${helpers.single_keyword("page-break-after",
                          "auto always avoid left right",
                          products="gecko",
+                         spec="https://drafts.csswg.org/css2/page.html#propdef-page-break-after",
                          animatable=False)}
 ${helpers.single_keyword("page-break-before",
                          "auto always avoid left right",
                          products="gecko",
+                         spec="https://drafts.csswg.org/css2/page.html#propdef-page-break-before",
                          animatable=False)}
 ${helpers.single_keyword("page-break-inside",
                          "auto avoid",
                          products="gecko",
                          gecko_ffi_name="mBreakInside",
                          gecko_constant_prefix="NS_STYLE_PAGE_BREAK",
+                         spec="https://drafts.csswg.org/css2/page.html#propdef-page-break-inside",
                          animatable=False)}
 
 // CSS Basic User Interface Module Level 3
-// http://dev.w3.org/csswg/css-ui/
+// http://dev.w3.org/csswg/css-ui
+// FIXME support logical values `block` and `inline` (https://drafts.csswg.org/css-logical-props/#resize)
 ${helpers.single_keyword("resize",
                          "none both horizontal vertical",
                          products="gecko",
+                         spec="https://drafts.csswg.org/css-ui/#propdef-resize",
                          animatable=False)}
 
 
-// https://drafts.csswg.org/css-transforms/#perspective
 ${helpers.predefined_type("perspective",
                           "LengthOrNone",
                           "Either::Second(None_)",
                           gecko_ffi_name="mChildPerspective",
+                          spec="https://drafts.csswg.org/css-transforms/#perspective",
                           animatable=True)}
 
 // FIXME: This prop should be animatable
-// https://drafts.csswg.org/css-transforms/#perspective-origin-property
-<%helpers:longhand name="perspective-origin" animatable="False">
+<%helpers:longhand name="perspective-origin" animatable="False"
+                   spec="https://drafts.csswg.org/css-transforms/#perspective-origin-property">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -1643,26 +1725,26 @@ ${helpers.predefined_type("perspective",
     }
 </%helpers:longhand>
 
-// https://drafts.csswg.org/css-transforms/#backface-visibility-property
 ${helpers.single_keyword("backface-visibility",
                          "visible hidden",
+                         spec="https://drafts.csswg.org/css-transforms/#backface-visibility-property",
                          animatable=False)}
 
-// https://drafts.csswg.org/css-transforms/#transform-box
 ${helpers.single_keyword("transform-box",
                          "border-box fill-box view-box",
                          products="gecko",
+                         spec="https://drafts.csswg.org/css-transforms/#transform-box",
                          animatable=False)}
 
 // `auto` keyword is not supported in gecko yet.
-// https://drafts.csswg.org/css-transforms/#transform-style-property
 ${helpers.single_keyword("transform-style",
                          "auto flat preserve-3d" if product == "servo" else
                          "flat preserve-3d",
+                         spec="https://drafts.csswg.org/css-transforms/#transform-style-property",
                          animatable=False)}
 
-// https://drafts.csswg.org/css-transforms/#transform-origin-property
-<%helpers:longhand name="transform-origin" animatable="True">
+<%helpers:longhand name="transform-origin" animatable="True"
+                   spec="https://drafts.csswg.org/css-transforms/#transform-origin-property">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
@@ -1795,18 +1877,19 @@ ${helpers.single_keyword("-moz-appearance",
                          gecko_ffi_name="mAppearance",
                          gecko_constant_prefix="NS_THEME",
                          products="gecko",
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-appearance)",
                          animatable=False)}
 
-// Non-standard: https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-binding
 ${helpers.predefined_type("-moz-binding", "UrlOrNone", "Either::Second(None_)",
                           products="gecko",
                           animatable="False",
+                          spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-binding)",
                           disable_when_testing="True")}
 
-// Non-standard: https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-orient
 ${helpers.single_keyword("-moz-orient",
                           "inline block horizontal vertical",
                           products="gecko",
                           gecko_ffi_name="mOrient",
                           gecko_enum_prefix="StyleOrient",
+                          spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-orient)",
                           animatable=False)}
diff --git a/components/style/properties/longhand/color.mako.rs b/components/style/properties/longhand/color.mako.rs
index 38c8e79f5ab..8012defab54 100644
--- a/components/style/properties/longhand/color.mako.rs
+++ b/components/style/properties/longhand/color.mako.rs
@@ -6,7 +6,8 @@
 
 <% data.new_style_struct("Color", inherited=True) %>
 
-<%helpers:raw_longhand name="color" need_clone="True" animatable="True">
+<%helpers:raw_longhand name="color" need_clone="True" animatable="True"
+                       spec="https://drafts.csswg.org/css-color/#color">
     use cssparser::Color as CSSParserColor;
     use cssparser::RGBA;
     use values::specified::{CSSColor, CSSRGBA};
diff --git a/components/style/properties/longhand/column.mako.rs b/components/style/properties/longhand/column.mako.rs
index ef2802be00d..a508a5daf9f 100644
--- a/components/style/properties/longhand/column.mako.rs
+++ b/components/style/properties/longhand/column.mako.rs
@@ -12,11 +12,13 @@ ${helpers.predefined_type("column-width",
                           "Either::Second(Auto)",
                           parse_method="parse_non_negative_length",
                           animatable=False,
-                          experimental=True)}
+                          experimental=True,
+                          spec="https://drafts.csswg.org/css-multicol/#propdef-column-width")}
 
 
 // FIXME: This prop should be animatable.
-<%helpers:longhand name="column-count" experimental="True" animatable="False">
+<%helpers:longhand name="column-count" experimental="True" animatable="False"
+                   spec="https://drafts.csswg.org/css-multicol/#propdef-column-count">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -101,13 +103,16 @@ ${helpers.predefined_type("column-gap",
                           "Either::Second(Normal)",
                           parse_method='parse_non_negative_length',
                           experimental=True,
-                          animatable=False)}
+                          animatable=False,
+                          spec="https://drafts.csswg.org/css-multicol/#propdef-column-gap")}
 
 ${helpers.single_keyword("column-fill", "auto balance",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://drafts.csswg.org/css-multicol/#propdef-column-gap")}
 
 // https://drafts.csswg.org/css-multicol-1/#propdef-column-rule-width
-<%helpers:longhand name="column-rule-width" products="gecko" animatable="True">
+<%helpers:longhand name="column-rule-width" products="gecko" animatable="True"
+                   spec="https://drafts.csswg.org/css-multicol/#propdef-column-rule-width">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
@@ -140,15 +145,17 @@ ${helpers.single_keyword("column-fill", "auto balance",
 ${helpers.predefined_type("column-rule-color", "CSSColor",
                           "::cssparser::Color::CurrentColor",
                           products="gecko", animatable=True,
-                          complex_color=True, need_clone=True)}
+                          complex_color=True, need_clone=True,
+                          spec="https://drafts.csswg.org/css-multicol/#propdef-column-rule-color")}
 
 // It's not implemented in servo or gecko yet.
-// https://drafts.csswg.org/css-multicol-1/#column-span
 ${helpers.single_keyword("column-span", "none all",
-                         products="none", animatable=False)}
+                         products="none", animatable=False,
+                         spec="https://drafts.csswg.org/css-multicol/#propdef-column-span")}
 
 ${helpers.single_keyword("column-rule-style",
                          "none hidden dotted dashed solid double groove ridge inset outset",
                          products="gecko",
                          gecko_constant_prefix="NS_STYLE_BORDER_STYLE",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-multicol/#propdef-column-rule-style")}
diff --git a/components/style/properties/longhand/counters.mako.rs b/components/style/properties/longhand/counters.mako.rs
index 521cb20cd4a..78c9fa8fc9e 100644
--- a/components/style/properties/longhand/counters.mako.rs
+++ b/components/style/properties/longhand/counters.mako.rs
@@ -6,7 +6,7 @@
 
 <% data.new_style_struct("Counters", inherited=False, gecko_name="Content") %>
 
-<%helpers:longhand name="content" animatable="False">
+<%helpers:longhand name="content" animatable="False" spec="https://drafts.csswg.org/css-content/#propdef-content">
     use cssparser::Token;
     use std::ascii::AsciiExt;
     use values::computed::ComputedValueAsSpecified;
@@ -174,7 +174,8 @@
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="counter-increment" products="servo" animatable="False">
+<%helpers:longhand name="counter-increment" products="servo" animatable="False"
+                   spec="https://drafts.csswg.org/css-lists/#propdef-counter-increment">
     use std::fmt;
     use style_traits::ToCss;
     use super::content;
@@ -247,7 +248,8 @@
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="counter-reset" products="servo" animatable="False">
+<%helpers:longhand name="counter-reset" products="servo" animatable="False"
+                   spec="https://drafts.csswg.org/css-lists-3/#propdef-counter-reset">
     pub use super::counter_increment::{SpecifiedValue, computed_value, get_initial_value};
     use super::counter_increment::{parse_common};
 
diff --git a/components/style/properties/longhand/effects.mako.rs b/components/style/properties/longhand/effects.mako.rs
index eff56c05a60..453199af08f 100644
--- a/components/style/properties/longhand/effects.mako.rs
+++ b/components/style/properties/longhand/effects.mako.rs
@@ -10,9 +10,11 @@
 ${helpers.predefined_type("opacity",
                           "Opacity",
                           "1.0",
-                          animatable=True)}
+                          animatable=True,
+                          spec="https://drafts.csswg.org/css-color/#opacity")}
 
-<%helpers:vector_longhand name="box-shadow" allow_empty="True" animatable="True">
+<%helpers:vector_longhand name="box-shadow" allow_empty="True" animatable="True"
+                          spec="https://drafts.csswg.org/css-backgrounds/#box-shadow">
     use cssparser;
     use std::fmt;
     use style_traits::ToCss;
@@ -74,7 +76,8 @@ ${helpers.predefined_type("opacity",
 </%helpers:vector_longhand>
 
 // FIXME: This prop should be animatable
-<%helpers:longhand name="clip" products="servo" animatable="False">
+<%helpers:longhand name="clip" products="servo" animatable="False"
+                   spec="https://drafts.fxtf.org/css-masking/#clip-property">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -287,7 +290,8 @@ ${helpers.predefined_type("opacity",
 </%helpers:longhand>
 
 // FIXME: This prop should be animatable
-<%helpers:longhand name="filter" animatable="False">
+<%helpers:longhand name="filter" animatable="False"
+                   spec="https://drafts.fxtf.org/filters/#propdef-filter">
     //pub use self::computed_value::T as SpecifiedValue;
     use cssparser;
     use std::fmt;
@@ -694,4 +698,5 @@ ${helpers.single_keyword("mix-blend-mode",
                          """normal multiply screen overlay darken lighten color-dodge
                             color-burn hard-light soft-light difference exclusion hue
                             saturation color luminosity""", gecko_constant_prefix="NS_STYLE_BLEND",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.fxtf.org/compositing/#propdef-mix-blend-mode")}
diff --git a/components/style/properties/longhand/font.mako.rs b/components/style/properties/longhand/font.mako.rs
index a247594ac58..b3dba9c3e1e 100644
--- a/components/style/properties/longhand/font.mako.rs
+++ b/components/style/properties/longhand/font.mako.rs
@@ -8,7 +8,8 @@
 <% data.new_style_struct("Font",
                          inherited=True,
                          additional_methods=[Method("compute_font_hash", is_mut=True)]) %>
-<%helpers:longhand name="font-family" animatable="False" need_index="True">
+<%helpers:longhand name="font-family" animatable="False" need_index="True"
+                   spec="https://drafts.csswg.org/css-fonts/#propdef-font-family">
     use self::computed_value::FontFamily;
     use values::NoViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
@@ -134,10 +135,12 @@ ${helpers.single_keyword("font-style",
                          "normal italic oblique",
                          gecko_constant_prefix="NS_FONT_STYLE",
                          gecko_ffi_name="mFont.style",
+                         spec="https://drafts.csswg.org/css-fonts/#propdef-font-style",
                          animatable=False)}
 
 ${helpers.single_keyword("font-variant",
                          "normal small-caps",
+                         spec="https://drafts.csswg.org/css-fonts/#propdef-font-variant",
                          animatable=False)}
 
 
@@ -152,10 +155,12 @@ ${helpers.single_keyword("font-variant-caps",
                          gecko_constant_prefix="NS_FONT_VARIANT_CAPS",
                          gecko_ffi_name="mFont.variantCaps",
                          products="gecko",
+                         spec="https://drafts.csswg.org/css-fonts/#propdef-font-variant-caps",
                          custom_consts=font_variant_caps_custom_consts,
                          animatable=False)}
 
-<%helpers:longhand name="font-weight" need_clone="True" animatable="True">
+<%helpers:longhand name="font-weight" need_clone="True" animatable="True"
+                   spec="https://drafts.csswg.org/css-fonts/#propdef-font-weight">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -288,7 +293,8 @@ ${helpers.single_keyword("font-variant-caps",
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="font-size" need_clone="True" animatable="True">
+<%helpers:longhand name="font-size" need_clone="True" animatable="True"
+                   spec="https://drafts.csswg.org/css-fonts/#propdef-font-size">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
@@ -370,8 +376,8 @@ ${helpers.single_keyword("font-variant-caps",
     }
 </%helpers:longhand>
 
-// https://www.w3.org/TR/css-fonts-3/#font-size-adjust-prop
-<%helpers:longhand products="gecko" name="font-size-adjust" animatable="True">
+<%helpers:longhand products="gecko" name="font-size-adjust" animatable="True"
+                   spec="https://drafts.csswg.org/css-fonts/#propdef-font-size-adjust">
     use values::NoViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
     use values::specified::Number;
@@ -430,7 +436,8 @@ ${helpers.single_keyword("font-variant-caps",
     }
 </%helpers:longhand>
 
-<%helpers:longhand products="gecko" name="font-synthesis" animatable="False">
+<%helpers:longhand products="gecko" name="font-synthesis" animatable="False"
+                   spec="https://drafts.csswg.org/css-fonts/#propdef-font-synthesis">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -500,6 +507,7 @@ ${helpers.single_keyword("font-stretch",
                          gecko_ffi_name="mFont.stretch",
                          gecko_constant_prefix="NS_FONT_STRETCH",
                          cast_type='i16',
+                         spec="https://drafts.csswg.org/css-fonts/#propdef-font-stretch",
                          animatable=False)}
 
 ${helpers.single_keyword("font-kerning",
@@ -507,6 +515,7 @@ ${helpers.single_keyword("font-kerning",
                          products="gecko",
                          gecko_ffi_name="mFont.kerning",
                          gecko_constant_prefix="NS_FONT_KERNING",
+                         spec="https://drafts.csswg.org/css-fonts/#propdef-font-stretch",
                          animatable=False)}
 
 ${helpers.single_keyword("font-variant-position",
@@ -514,9 +523,11 @@ ${helpers.single_keyword("font-variant-position",
                          products="gecko",
                          gecko_ffi_name="mFont.variantPosition",
                          gecko_constant_prefix="NS_FONT_VARIANT_POSITION",
+                         spec="https://drafts.csswg.org/css-fonts/#propdef-font-variant-position",
                          animatable=False)}
 
-<%helpers:longhand name="font-feature-settings" products="none" animatable="False">
+<%helpers:longhand name="font-feature-settings" products="none" animatable="False"
+                   spec="https://drafts.csswg.org/css-fonts/#propdef-font-feature-settings">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -626,7 +637,8 @@ ${helpers.single_keyword("font-variant-position",
 </%helpers:longhand>
 
 // https://www.w3.org/TR/css-fonts-3/#propdef-font-language-override
-<%helpers:longhand name="font-language-override" products="none" animatable="False">
+<%helpers:longhand name="font-language-override" products="none" animatable="False"
+                   spec="https://drafts.csswg.org/css-fonts-3/#propdef-font-language-override">
     use values::NoViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
     pub use self::computed_value::T as SpecifiedValue;
diff --git a/components/style/properties/longhand/inherited_box.mako.rs b/components/style/properties/longhand/inherited_box.mako.rs
index 7eca5ab0ee5..01d51aeacce 100644
--- a/components/style/properties/longhand/inherited_box.mako.rs
+++ b/components/style/properties/longhand/inherited_box.mako.rs
@@ -6,22 +6,25 @@
 
 <% data.new_style_struct("InheritedBox", inherited=True, gecko_name="Visibility") %>
 
-${helpers.single_keyword("direction", "ltr rtl", need_clone=True, animatable=False)}
-
 // TODO: collapse. Well, do tables first.
 ${helpers.single_keyword("visibility",
                          "visible hidden",
                          extra_gecko_values="collapse",
                          gecko_ffi_name="mVisible",
-                         animatable=True)}
+                         animatable=True,
+                         spec="https://drafts.csswg.org/css-box/#propdef-visibility")}
 
 // CSS Writing Modes Level 3
-// http://dev.w3.org/csswg/css-writing-modes/
+// https://drafts.csswg.org/css-writing-modes-3
 ${helpers.single_keyword("writing-mode",
                          "horizontal-tb vertical-rl vertical-lr",
                          experimental=True,
                          need_clone=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-writing-modes/#propdef-writing-mode")}
+
+${helpers.single_keyword("direction", "ltr rtl", need_clone=True, animatable=False,
+                         spec="https://drafts.csswg.org/css-writing-modes/#propdef-direction")}
 
 // FIXME(SimonSapin): Add 'mixed' and 'upright' (needs vertical text support)
 // FIXME(SimonSapin): initial (first) value should be 'mixed', when that's implemented
@@ -32,13 +35,15 @@ ${helpers.single_keyword("text-orientation",
                          need_clone=True,
                          extra_gecko_values="mixed upright",
                          extra_servo_values="sideways-right sideways-left",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-writing-modes/#propdef-text-orientation")}
 
 // CSS Color Module Level 4
 // https://drafts.csswg.org/css-color/
 ${helpers.single_keyword("color-adjust",
                          "economy exact", products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-color/#propdef-color-adjust")}
 
 <% image_rendering_custom_consts = { "crisp-edges": "CRISPEDGES" } %>
 // According to to CSS-IMAGES-3, `optimizespeed` and `optimizequality` are synonyms for `auto`
@@ -48,13 +53,15 @@ ${helpers.single_keyword("image-rendering",
                          extra_gecko_values="optimizespeed optimizequality",
                          extra_servo_values="pixelated",
                          custom_consts=image_rendering_custom_consts,
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-images/#propdef-image-rendering")}
 
 // Image Orientation
-// https://drafts.csswg.org/css-images/#the-image-orientation
 <%helpers:longhand name="image-orientation"
                    products="None"
-                   animatable="False">
+                   animatable="False"
+    spec="https://drafts.csswg.org/css-images/#propdef-image-orientation, \
+      /// additional values in https://developer.mozilla.org/en-US/docs/Web/CSS/image-orientation">
     use std::fmt;
     use style_traits::ToCss;
     use values::specified::Angle;
@@ -188,7 +195,8 @@ ${helpers.single_keyword("image-rendering",
 <%helpers:longhand name="-servo-under-display-none"
                    derived_from="display"
                    products="servo"
-                   animatable="False">
+                   animatable="False"
+                   spec="Nonstandard (internal layout use only)">
     use std::fmt;
     use style_traits::ToCss;
     use values::computed::ComputedValueAsSpecified;
diff --git a/components/style/properties/longhand/inherited_svg.mako.rs b/components/style/properties/longhand/inherited_svg.mako.rs
index 6a0b00eced9..56987f0ba75 100644
--- a/components/style/properties/longhand/inherited_svg.mako.rs
+++ b/components/style/properties/longhand/inherited_svg.mako.rs
@@ -17,49 +17,60 @@
 ${helpers.single_keyword("text-anchor",
                          "start middle end",
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://www.w3.org/TR/SVG/text.html#TextAnchorProperty")}
 
 // Section 11 - Painting: Filling, Stroking and Marker Symbols
 ${helpers.single_keyword("color-interpolation",
                          "auto sRGB linearRGB",
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#ColorInterpolationProperty")}
 
 ${helpers.single_keyword("color-interpolation-filters", "auto sRGB linearRGB",
                          products="gecko",
                          gecko_constant_prefix="NS_STYLE_COLOR_INTERPOLATION",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#ColorInterpolationFiltersProperty")}
 
 ${helpers.predefined_type("fill-opacity", "Opacity", "1.0",
-                          products="gecko", animatable=False)}
+                          products="gecko", animatable=False,
+                          spec="https://www.w3.org/TR/SVG11/painting.html#FillOpacityProperty")}
 
 ${helpers.single_keyword("fill-rule", "nonzero evenodd",
                          gecko_enum_prefix="StyleFillRule",
                          gecko_inexhaustive=True,
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#FillRuleProperty")}
 
 ${helpers.single_keyword("shape-rendering",
                          "auto optimizeSpeed crispEdges geometricPrecision",
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#ShapeRenderingProperty")}
 
 ${helpers.single_keyword("stroke-linecap", "butt round square",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#StrokeLinecapProperty")}
 
 ${helpers.single_keyword("stroke-linejoin", "miter round bevel",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#StrokeLinejoinProperty")}
 
 ${helpers.predefined_type("stroke-miterlimit", "Number", "4.0",
                           "parse_at_least_one", products="gecko",
                           needs_context=False,
-                          animatable=False)}
+                          animatable=False,
+                          spec="https://www.w3.org/TR/SVG11/painting.html#StrokeMiterlimitProperty")}
 
 ${helpers.predefined_type("stroke-opacity", "Opacity", "1.0",
-                          products="gecko", animatable=False)}
+                          products="gecko", animatable=False,
+                          spec="https://www.w3.org/TR/SVG11/painting.html#StrokeOpacityProperty")}
 
 // Section 14 - Clipping, Masking and Compositing
 ${helpers.single_keyword("clip-rule", "nonzero evenodd",
                          products="gecko",
                          gecko_enum_prefix="StyleFillRule",
                          gecko_inexhaustive=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/masking.html#ClipRuleProperty")}
diff --git a/components/style/properties/longhand/inherited_table.mako.rs b/components/style/properties/longhand/inherited_table.mako.rs
index a8b3e6f8913..125477b4c46 100644
--- a/components/style/properties/longhand/inherited_table.mako.rs
+++ b/components/style/properties/longhand/inherited_table.mako.rs
@@ -8,15 +8,19 @@
 
 ${helpers.single_keyword("border-collapse", "separate collapse",
                          gecko_constant_prefix="NS_STYLE_BORDER",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-tables/#propdef-border-collapse")}
 ${helpers.single_keyword("empty-cells", "show hide",
                          gecko_constant_prefix="NS_STYLE_TABLE_EMPTY_CELLS",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-tables/#propdef-empty-cells")}
 ${helpers.single_keyword("caption-side", "top bottom",
                          extra_gecko_values="right left top-outside bottom-outside",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-tables/#propdef-caption-side")}
 
-<%helpers:longhand name="border-spacing" animatable="False">
+<%helpers:longhand name="border-spacing" animatable="False"
+                   spec="https://drafts.csswg.org/css-tables/#propdef-border-spacing">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
diff --git a/components/style/properties/longhand/inherited_text.mako.rs b/components/style/properties/longhand/inherited_text.mako.rs
index 21a769514e5..32e5c91b7d0 100644
--- a/components/style/properties/longhand/inherited_text.mako.rs
+++ b/components/style/properties/longhand/inherited_text.mako.rs
@@ -6,7 +6,8 @@
 
 <% data.new_style_struct("InheritedText", inherited=True, gecko_name="Text") %>
 
-<%helpers:longhand name="line-height" animatable="True">
+<%helpers:longhand name="line-height" animatable="True"
+                   spec="https://drafts.csswg.org/css2/visudet.html#propdef-line-height">
     use std::fmt;
     use style_traits::ToCss;
     use values::{CSSFloat, HasViewportPercentage};
@@ -144,7 +145,56 @@
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="text-align" animatable="False">
+// CSS Text Module Level 3
+
+// TODO(pcwalton): `full-width`
+${helpers.single_keyword("text-transform",
+                         "none capitalize uppercase lowercase",
+                         extra_gecko_values="full-width",
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-text/#propdef-text-transform")}
+
+${helpers.single_keyword("hyphens", "none manual auto",
+                         products="gecko", animatable=False,
+                         spec="https://drafts.csswg.org/css-text/#propdef-hyphens")}
+
+${helpers.predefined_type("text-indent",
+                          "LengthOrPercentage",
+                          "computed::LengthOrPercentage::Length(Au(0))",
+                          animatable=True,
+                          spec="https://drafts.csswg.org/css-text/#propdef-text-indent")}
+
+// Also known as "word-wrap" (which is more popular because of IE), but this is the preferred
+// name per CSS-TEXT 6.2.
+${helpers.single_keyword("overflow-wrap",
+                         "normal break-word",
+                         gecko_constant_prefix="NS_STYLE_OVERFLOWWRAP",
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-text/#propdef-overflow-wrap")}
+
+// TODO(pcwalton): Support `word-break: keep-all` once we have better CJK support.
+${helpers.single_keyword("word-break",
+                         "normal break-all keep-all",
+                         gecko_constant_prefix="NS_STYLE_WORDBREAK",
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-text/#propdef-word-break")}
+
+// TODO(pcwalton): Support `text-justify: distribute`.
+${helpers.single_keyword("text-justify",
+                         "auto none inter-word",
+                         products="servo",
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-text/#propdef-text-justify")}
+
+${helpers.single_keyword("text-align-last",
+                         "auto start end left right center justify",
+                         products="gecko",
+                         gecko_constant_prefix="NS_STYLE_TEXT_ALIGN",
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-text/#propdef-text-align-last")}
+
+// TODO make this a shorthand and implement text-align-last/text-align-all
+<%helpers:longhand name="text-align" animatable="False" spec="https://drafts.csswg.org/css-text/#propdef-text-align">
     pub use self::computed_value::T as SpecifiedValue;
     use values::computed::ComputedValueAsSpecified;
     use values::NoViewportPercentage;
@@ -206,7 +256,8 @@
 </%helpers:longhand>
 
 // FIXME: This prop should be animatable.
-<%helpers:longhand name="letter-spacing" animatable="False">
+<%helpers:longhand name="letter-spacing" animatable="False"
+                   spec="https://drafts.csswg.org/css-text/#propdef-letter-spacing">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -286,7 +337,8 @@
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="word-spacing" animatable="False">
+<%helpers:longhand name="word-spacing" animatable="False"
+                   spec="https://drafts.csswg.org/css-text/#propdef-word-spacing">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -367,40 +419,11 @@
     }
 </%helpers:longhand>
 
-${helpers.predefined_type("text-indent",
-                          "LengthOrPercentage",
-                          "computed::LengthOrPercentage::Length(Au(0))",
-                          animatable=True)}
-
-// Also known as "word-wrap" (which is more popular because of IE), but this is the preferred
-// name per CSS-TEXT 6.2.
-${helpers.single_keyword("overflow-wrap",
-                         "normal break-word",
-                         gecko_constant_prefix="NS_STYLE_OVERFLOWWRAP",
-                         animatable=False)}
-
-// TODO(pcwalton): Support `word-break: keep-all` once we have better CJK support.
-${helpers.single_keyword("word-break",
-                         "normal break-all keep-all",
-                         gecko_constant_prefix="NS_STYLE_WORDBREAK",
-                         animatable=False)}
-
-// TODO(pcwalton): Support `text-justify: distribute`.
-${helpers.single_keyword("text-justify",
-                         "auto none inter-word",
-                         products="servo",
-                         animatable=False)}
-
-${helpers.single_keyword("text-align-last",
-                         "auto start end left right center justify",
-                         products="gecko",
-                         gecko_constant_prefix="NS_STYLE_TEXT_ALIGN",
-                         animatable=False)}
-
 <%helpers:longhand name="-servo-text-decorations-in-effect"
                    derived_from="display text-decoration"
                    need_clone="True" products="servo"
-                   animatable="False">
+                   animatable="False"
+                   spec="Nonstandard (Internal property used by Servo)">
     use cssparser::RGBA;
     use std::fmt;
     use style_traits::ToCss;
@@ -485,7 +508,8 @@ ${helpers.single_keyword("text-align-last",
 <%helpers:single_keyword_computed name="white-space"
                                   values="normal pre nowrap pre-wrap pre-line"
                                   gecko_constant_prefix="NS_STYLE_WHITESPACE"
-                                  animatable="False">
+                                  animatable="False"
+                                  spec="https://drafts.csswg.org/css-text/#propdef-white-space">
     use values::computed::ComputedValueAsSpecified;
     use values::NoViewportPercentage;
     impl ComputedValueAsSpecified for SpecifiedValue {}
@@ -524,7 +548,8 @@ ${helpers.single_keyword("text-align-last",
     }
 </%helpers:single_keyword_computed>
 
-<%helpers:longhand name="text-shadow" animatable="True">
+<%helpers:longhand name="text-shadow" animatable="True"
+                   spec="https://drafts.csswg.org/css-text-decor/#propdef-text-shadow">
     use cssparser;
     use std::fmt;
     use style_traits::ToCss;
@@ -733,7 +758,8 @@ ${helpers.single_keyword("text-align-last",
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="text-emphasis-style" products="gecko" need_clone="True" animatable="False">
+<%helpers:longhand name="text-emphasis-style" products="gecko" need_clone="True" animatable="False"
+                   spec="https://drafts.csswg.org/css-text-decor/#propdef-text-emphasis-style">
     use computed_values::writing_mode::T as writing_mode;
     use std::fmt;
     use style_traits::ToCss;
@@ -940,7 +966,8 @@ ${helpers.single_keyword("text-align-last",
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="text-emphasis-position" animatable="False" products="none">
+<%helpers:longhand name="text-emphasis-position" animatable="False" products="none"
+                   spec="https://drafts.csswg.org/css-text-decor/#propdef-text-emphasis-position">
     use std::fmt;
     use values::computed::ComputedValueAsSpecified;
     use values::NoViewportPercentage;
@@ -989,31 +1016,30 @@ ${helpers.single_keyword("text-align-last",
     }
 </%helpers:longhand>
 
-// https://drafts.csswg.org/css-text-decor-3/#text-emphasis-color-property
 ${helpers.predefined_type("text-emphasis-color", "CSSColor",
                           "::cssparser::Color::CurrentColor",
                           products="gecko",animatable=True,
-                          complex_color=True, need_clone=True)}
+                          complex_color=True, need_clone=True,
+                          spec="https://drafts.csswg.org/css-text-decor/#propdef-text-emphasis-color")}
 
 // CSS Compatibility
-// https://compat.spec.whatwg.org/#the-webkit-text-fill-color
+// https://compat.spec.whatwg.org
 ${helpers.predefined_type(
     "-webkit-text-fill-color", "CSSColor",
     "CSSParserColor::CurrentColor",
     products="gecko", animatable=True,
-    complex_color=True, need_clone=True)}
+    complex_color=True, need_clone=True,
+    spec="https://compat.spec.whatwg.org/#the-webkit-text-fill-color")}
 
-// CSS Compatibility
-// https://compat.spec.whatwg.org/#the-webkit-text-stroke-color
 ${helpers.predefined_type(
     "-webkit-text-stroke-color", "CSSColor",
     "CSSParserColor::CurrentColor",
     products="gecko", animatable=True,
-    complex_color=True, need_clone=True)}
+    complex_color=True, need_clone=True,
+    spec="https://compat.spec.whatwg.org/#the-webkit-text-stroke-color")}
 
-// CSS Compatibility
-// https://compat.spec.whatwg.org/#the-webkit-text-stroke-width
-<%helpers:longhand products="gecko" name="-webkit-text-stroke-width" animatable="False">
+<%helpers:longhand products="gecko" name="-webkit-text-stroke-width" animatable="False"
+                   spec="https://compat.spec.whatwg.org/#the-webkit-text-stroke-width">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
@@ -1036,33 +1062,28 @@ ${helpers.predefined_type(
     }
 </%helpers:longhand>
 
-// TODO(pcwalton): `full-width`
-${helpers.single_keyword("text-transform",
-                         "none capitalize uppercase lowercase",
-                         extra_gecko_values="full-width",
-                         animatable=False)}
-
-${helpers.single_keyword("text-rendering",
-                         "auto optimizespeed optimizelegibility geometricprecision",
-                         animatable=False)}
-
-// CSS Text Module Level 3
-// https://www.w3.org/TR/css-text-3/
-${helpers.single_keyword("hyphens", "none manual auto",
-                         products="gecko", animatable=False)}
-
 // CSS Ruby Layout Module Level 1
-// https://www.w3.org/TR/css-ruby-1/
+// https://drafts.csswg.org/css-ruby/
 ${helpers.single_keyword("ruby-align", "start center space-between space-around",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://drafts.csswg.org/css-ruby/#ruby-align-property")}
 
 ${helpers.single_keyword("ruby-position", "over under",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://drafts.csswg.org/css-ruby/#ruby-position-property")}
 
 // CSS Writing Modes Module Level 3
-// https://drafts.csswg.org/css-writing-modes-3/#text-combine-upright
+// https://drafts.csswg.org/css-writing-modes-3/
+
 // The spec has "digits <integer>?" value in addition. But that value is
 // at-risk, and Gecko's layout code doesn't support that either. So we
 // can just take the easy way for now.
 ${helpers.single_keyword("text-combine-upright", "none all",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://drafts.csswg.org/css-writing-modes-3/#text-combine-upright")}
+
+// SVG 1.1: Section 11 - Painting: Filling, Stroking and Marker Symbols
+${helpers.single_keyword("text-rendering",
+                         "auto optimizespeed optimizelegibility geometricprecision",
+                         animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/painting.html#TextRenderingProperty")}
diff --git a/components/style/properties/longhand/list.mako.rs b/components/style/properties/longhand/list.mako.rs
index b62e7222cb8..9f19d80aec7 100644
--- a/components/style/properties/longhand/list.mako.rs
+++ b/components/style/properties/longhand/list.mako.rs
@@ -6,7 +6,8 @@
 
 <% data.new_style_struct("List", inherited=True) %>
 
-${helpers.single_keyword("list-style-position", "outside inside", animatable=False)}
+${helpers.single_keyword("list-style-position", "outside inside", animatable=False,
+                         spec="https://drafts.csswg.org/css-lists/#propdef-list-style-position")}
 
 // TODO(pcwalton): Implement the full set of counter styles per CSS-COUNTER-STYLES [1] 6.1:
 //
@@ -24,12 +25,15 @@ ${helpers.single_keyword("list-style-type", """
                            cjk-heavenly-stem lower-greek hiragana hiragana-iroha katakana
                            katakana-iroha lower-alpha upper-alpha""",
     gecko_constant_prefix="NS_STYLE_LIST_STYLE",
-    animatable=False)}
+    animatable=False,
+    spec="https://drafts.csswg.org/css-lists/#propdef-list-style-type")}
 
 ${helpers.predefined_type("list-style-image", "UrlOrNone", "Either::Second(None_)",
-                          animatable="False")}
+                          animatable="False",
+                          spec="https://drafts.csswg.org/css-lists/#propdef-list-style-image")}
 
-<%helpers:longhand name="quotes" animatable="False">
+<%helpers:longhand name="quotes" animatable="False"
+                   spec="https://drafts.csswg.org/css-content/#propdef-quotes">
     use cssparser::Token;
     use std::borrow::Cow;
     use std::fmt;
diff --git a/components/style/properties/longhand/margin.mako.rs b/components/style/properties/longhand/margin.mako.rs
index 8ddc676d21f..810386ae023 100644
--- a/components/style/properties/longhand/margin.mako.rs
+++ b/components/style/properties/longhand/margin.mako.rs
@@ -7,7 +7,12 @@
 <% data.new_style_struct("Margin", inherited=False) %>
 
 % for side in ALL_SIDES:
+    <%
+        spec = "https://drafts.csswg.org/css-box/#propdef-margin-%s" % side[0]
+        if side[1]:
+            spec = "https://drafts.csswg.org/css-logical-props/#propdef-margin-%s" % side[1]
+    %>
     ${helpers.predefined_type("margin-%s" % side[0], "LengthOrPercentageOrAuto",
                               "computed::LengthOrPercentageOrAuto::Length(Au(0))",
-                              animatable=True, logical = side[1])}
+                              animatable=True, logical = side[1], spec = spec)}
 % endfor
diff --git a/components/style/properties/longhand/outline.mako.rs b/components/style/properties/longhand/outline.mako.rs
index 73057ab7c33..06b91acbca8 100644
--- a/components/style/properties/longhand/outline.mako.rs
+++ b/components/style/properties/longhand/outline.mako.rs
@@ -11,9 +11,11 @@
 
 // TODO(pcwalton): `invert`
 ${helpers.predefined_type("outline-color", "CSSColor", "::cssparser::Color::CurrentColor",
-                          animatable=True, complex_color=True, need_clone=True)}
+                          animatable=True, complex_color=True, need_clone=True,
+                          spec="https://drafts.csswg.org/css-ui/#propdef-outline-color")}
 
-<%helpers:longhand name="outline-style" need_clone="True" animatable="False">
+<%helpers:longhand name="outline-style" need_clone="True" animatable="False"
+                   spec="https://drafts.csswg.org/css-ui/#propdef-outline-style">
     pub use values::specified::BorderStyle as SpecifiedValue;
     pub fn get_initial_value() -> SpecifiedValue { SpecifiedValue::none }
     pub mod computed_value {
@@ -27,7 +29,8 @@ ${helpers.predefined_type("outline-color", "CSSColor", "::cssparser::Color::Curr
     }
 </%helpers:longhand>
 
-<%helpers:longhand name="outline-width" animatable="True">
+<%helpers:longhand name="outline-width" animatable="True"
+                   spec="https://drafts.csswg.org/css-ui/#propdef-outline-width">
     use app_units::Au;
     use std::fmt;
     use style_traits::ToCss;
@@ -77,9 +80,11 @@ ${helpers.predefined_type("outline-color", "CSSColor", "::cssparser::Color::Curr
 // TODO: Should they animate?
 % for corner in ["topleft", "topright", "bottomright", "bottomleft"]:
     ${helpers.predefined_type("-moz-outline-radius-" + corner, "BorderRadiusSize",
-                              "computed::BorderRadiusSize::zero()",
-                              "parse", products="gecko",
-                              animatable=False)}
+        "computed::BorderRadiusSize::zero()",
+        "parse", products="gecko",
+        animatable=False,
+        spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-outline-radius)")}
 % endfor
 
-${helpers.predefined_type("outline-offset", "Length", "Au(0)", products="servo", animatable=True)}
+${helpers.predefined_type("outline-offset", "Length", "Au(0)", products="servo", animatable=True,
+                          spec="https://drafts.csswg.org/css-ui/#propdef-outline-offset")}
diff --git a/components/style/properties/longhand/padding.mako.rs b/components/style/properties/longhand/padding.mako.rs
index b0778bde34b..1f029f53192 100644
--- a/components/style/properties/longhand/padding.mako.rs
+++ b/components/style/properties/longhand/padding.mako.rs
@@ -7,10 +7,16 @@
 <% data.new_style_struct("Padding", inherited=False) %>
 
 % for side in ALL_SIDES:
+    <%
+        spec = "https://drafts.csswg.org/css-box/#propdef-padding-%s" % side[0]
+        if side[1]:
+            spec = "https://drafts.csswg.org/css-logical-props/#propdef-padding-%s" % side[1]
+    %>
     ${helpers.predefined_type("padding-%s" % side[0], "LengthOrPercentage",
                                "computed::LengthOrPercentage::Length(Au(0))",
                                "parse_non_negative",
                                needs_context=False,
                                animatable=True,
-                               logical = side[1])}
+                               logical = side[1],
+                               spec = spec)}
 % endfor
diff --git a/components/style/properties/longhand/pointing.mako.rs b/components/style/properties/longhand/pointing.mako.rs
index 412e2fe080c..6e202da6242 100644
--- a/components/style/properties/longhand/pointing.mako.rs
+++ b/components/style/properties/longhand/pointing.mako.rs
@@ -6,7 +6,7 @@
 
 <% data.new_style_struct("Pointing", inherited=True, gecko_name="UserInterface") %>
 
-<%helpers:longhand name="cursor" animatable="False">
+<%helpers:longhand name="cursor" animatable="False" spec="https://drafts.csswg.org/css-ui/#cursor">
     pub use self::computed_value::T as SpecifiedValue;
     use values::NoViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
@@ -146,23 +146,27 @@
 // NB: `pointer-events: auto` (and use of `pointer-events` in anything that isn't SVG, in fact)
 // is nonstandard, slated for CSS4-UI.
 // TODO(pcwalton): SVG-only values.
-${helpers.single_keyword("pointer-events", "auto none", animatable=False)}
+${helpers.single_keyword("pointer-events", "auto none", animatable=False,
+                         spec="https://www.w3.org/TR/SVG11/interact.html#PointerEventsProperty")}
 
 ${helpers.single_keyword("-moz-user-input", "none enabled disabled",
                          products="gecko", gecko_ffi_name="mUserInput",
                          gecko_enum_prefix="StyleUserInput",
                          gecko_inexhaustive=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-user-input)")}
 
 ${helpers.single_keyword("-moz-user-modify", "read-only read-write write-only",
                          products="gecko", gecko_ffi_name="mUserModify",
                          gecko_enum_prefix="StyleUserModify",
                          gecko_inexhaustive=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-user-modify)")}
 
 ${helpers.single_keyword("-moz-user-focus",
                          "ignore normal select-after select-before select-menu select-same select-all none",
                          products="gecko", gecko_ffi_name="mUserFocus",
                          gecko_enum_prefix="StyleUserFocus",
                          gecko_inexhaustive=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-user-focus)")}
diff --git a/components/style/properties/longhand/position.mako.rs b/components/style/properties/longhand/position.mako.rs
index f025e658c5b..bad7e9737a5 100644
--- a/components/style/properties/longhand/position.mako.rs
+++ b/components/style/properties/longhand/position.mako.rs
@@ -12,16 +12,18 @@
 % for side in PHYSICAL_SIDES:
     ${helpers.predefined_type(side, "LengthOrPercentageOrAuto",
                               "computed::LengthOrPercentageOrAuto::Auto",
+                              spec="https://www.w3.org/TR/CSS2/visuren.html#propdef-%s" % side,
                               animatable=True)}
 % endfor
 // offset-* logical properties, map to "top" / "left" / "bottom" / "right"
 % for side in LOGICAL_SIDES:
-    ${helpers.predefined_type("offset-" + side, "LengthOrPercentageOrAuto",
+    ${helpers.predefined_type("offset-%s" % side, "LengthOrPercentageOrAuto",
                               "computed::LengthOrPercentageOrAuto::Auto",
+                              spec="https://drafts.csswg.org/css-logical-props/#propdef-offset-%s" % side,
                               animatable=True, logical=True)}
 % endfor
 
-<%helpers:longhand name="z-index" animatable="True">
+<%helpers:longhand name="z-index" spec="https://www.w3.org/TR/CSS2/visuren.html#z-index" animatable="True">
     use values::NoViewportPercentage;
     use values::computed::ComputedValueAsSpecified;
 
@@ -75,9 +77,11 @@
 
 // Flex container properties
 ${helpers.single_keyword("flex-direction", "row row-reverse column column-reverse",
+                         spec="https://drafts.csswg.org/css-flexbox/#flex-direction-property",
                          animatable=False)}
 
 ${helpers.single_keyword("flex-wrap", "nowrap wrap wrap-reverse",
+                         spec="https://drafts.csswg.org/css-flexbox/#flex-wrap-property",
                          animatable=False)}
 
 // FIXME(stshine): The type of 'justify-content' and 'align-content' is uint16_t in gecko
@@ -85,6 +89,7 @@ ${helpers.single_keyword("flex-wrap", "nowrap wrap wrap-reverse",
 ${helpers.single_keyword("justify-content", "flex-start flex-end center space-between space-around",
                          gecko_constant_prefix="NS_STYLE_JUSTIFY",
                          products="servo",
+                         spec="https://drafts.csswg.org/css-flexbox/#justify-content-property",
                          animatable=False)}
 
 // https://drafts.csswg.org/css-flexbox/#propdef-align-items
@@ -93,21 +98,25 @@ ${helpers.single_keyword("align-items", "stretch flex-start flex-end center base
                          else "normal stretch flex-start flex-end center baseline",
                          need_clone=True,
                          gecko_constant_prefix="NS_STYLE_ALIGN",
+                         spec="https://drafts.csswg.org/css-flexbox/#align-items-property",
                          animatable=False)}
 
 ${helpers.single_keyword("align-content", "stretch flex-start flex-end center space-between space-around",
                          gecko_constant_prefix="NS_STYLE_ALIGN",
                          products="servo",
+                         spec="https://drafts.csswg.org/css-flexbox/#align-content-property",
                          animatable=False)}
 
 // Flex item properties
 ${helpers.predefined_type("flex-grow", "Number",
                           "0.0", "parse_non_negative",
+                          spec="https://drafts.csswg.org/css-flexbox/#flex-grow-property",
                           needs_context=False,
                           animatable=True)}
 
 ${helpers.predefined_type("flex-shrink", "Number",
                           "1.0", "parse_non_negative",
+                          spec="https://drafts.csswg.org/css-flexbox/#flex-shrink-property",
                           needs_context=False,
                           animatable=True)}
 
@@ -117,10 +126,12 @@ ${helpers.single_keyword("align-self", "auto stretch flex-start flex-end center
                          need_clone=True,
                          extra_gecko_values="normal",
                          gecko_constant_prefix="NS_STYLE_ALIGN",
+                         spec="https://drafts.csswg.org/css-flexbox/#propdef-align-self",
                          animatable=False)}
 
 // https://drafts.csswg.org/css-flexbox/#propdef-order
-<%helpers:longhand name="order" animatable="True">
+<%helpers:longhand name="order" animatable="True"
+                   spec="https://drafts.csswg.org/css-flexbox/#order-property">
     use values::computed::ComputedValueAsSpecified;
 
     impl ComputedValueAsSpecified for SpecifiedValue {}
@@ -145,15 +156,22 @@ ${helpers.single_keyword("align-self", "auto stretch flex-start flex-end center
 ${helpers.predefined_type("flex-basis",
                           "LengthOrPercentageOrAutoOrContent",
                           "computed::LengthOrPercentageOrAutoOrContent::Auto",
+                          spec="https://drafts.csswg.org/css-flexbox/#flex-basis-property",
                           animatable=False)}
 
 % for (size, logical) in ALL_SIZES:
+    <%
+      spec = "https://drafts.csswg.org/css-box/#propdef-%s"
+      if logical:
+        spec = "https://drafts.csswg.org/css-logical-props/#propdef-%s"
+    %>
     // width, height, block-size, inline-size
     ${helpers.predefined_type("%s" % size,
                               "LengthOrPercentageOrAuto",
                               "computed::LengthOrPercentageOrAuto::Auto",
                               "parse_non_negative",
                               needs_context=False,
+                              spec=spec % size,
                               animatable=True, logical = logical)}
 
     // min-width, min-height, min-block-size, min-inline-size
@@ -162,6 +180,7 @@ ${helpers.predefined_type("flex-basis",
                               "computed::LengthOrPercentage::Length(Au(0))",
                               "parse_non_negative",
                               needs_context=False,
+                              spec=spec % ("min-%s" % size),
                               animatable=True, logical = logical)}
 
     // max-width, max-height, max-block-size, max-inline-size
@@ -170,19 +189,19 @@ ${helpers.predefined_type("flex-basis",
                               "computed::LengthOrPercentageOrNone::None",
                               "parse_non_negative",
                               needs_context=False,
+                              spec=spec % ("max-%s" % size),
                               animatable=True, logical = logical)}
 % endfor
 
 ${helpers.single_keyword("box-sizing",
                          "content-box border-box",
+                         spec="https://drafts.csswg.org/css-ui/#propdef-box-sizing",
                          animatable=False)}
 
-// CSS Image Values and Replaced Content Module Level 3
-// https://drafts.csswg.org/css-images-3/
 ${helpers.single_keyword("object-fit", "fill contain cover none scale-down",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://drafts.csswg.org/css-images/#propdef-object-fit")}
 
-// https://drafts.csswg.org/css-grid/#propdef-grid-row-start
 <% grid_longhands = ["grid-row-start", "grid-row-end", "grid-column-start", "grid-column-end"] %>
 
 % for longhand in grid_longhands:
@@ -190,5 +209,6 @@ ${helpers.single_keyword("object-fit", "fill contain cover none scale-down",
                               "GridLine",
                               "Default::default()",
                               animatable=False,
+                              spec="https://drafts.csswg.org/css-grid/#propdef-%s" % longhand,
                               products="gecko")}
 % endfor
diff --git a/components/style/properties/longhand/svg.mako.rs b/components/style/properties/longhand/svg.mako.rs
index dcab70f6b34..959ccb2db41 100644
--- a/components/style/properties/longhand/svg.mako.rs
+++ b/components/style/properties/longhand/svg.mako.rs
@@ -11,10 +11,12 @@ ${helpers.single_keyword("dominant-baseline",
                  """auto use-script no-change reset-size ideographic alphabetic hanging
                     mathematical central middle text-after-edge text-before-edge""",
                  products="gecko",
-                 animatable=False)}
+                 animatable=False,
+                 spec="https://www.w3.org/TR/SVG11/text.html#DominantBaselineProperty")}
 
 ${helpers.single_keyword("vector-effect", "none non-scaling-stroke",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://www.w3.org/TR/SVGTiny12/painting.html#VectorEffectProperty")}
 
 // Section 13 - Gradients and Patterns
 
@@ -22,11 +24,13 @@ ${helpers.predefined_type(
     "stop-color", "CSSColor",
     "CSSParserColor::RGBA(RGBA { red: 0.0, green: 0.0, blue: 0.0, alpha: 1.0 })",
     products="gecko",
-    animatable=False)}
+    animatable=False,
+    spec="https://www.w3.org/TR/SVGTiny12/painting.html#StopColorProperty")}
 
 ${helpers.predefined_type("stop-opacity", "Opacity", "1.0",
                           products="gecko",
-                          animatable=False)}
+                          animatable=False,
+                          spec="https://www.w3.org/TR/SVGTiny12/painting.html#propdef-stop-opacity")}
 
 // Section 15 - Filter Effects
 
@@ -34,23 +38,28 @@ ${helpers.predefined_type(
     "flood-color", "CSSColor",
     "CSSParserColor::RGBA(RGBA { red: 0.0, green: 0.0, blue: 0.0, alpha: 1.0 })",
     products="gecko",
-    animatable=False)}
+    animatable=False,
+    spec="https://www.w3.org/TR/SVG/filters.html#FloodColorProperty")}
 
 ${helpers.predefined_type("flood-opacity", "Opacity",
-                          "1.0", products="gecko", animatable=False)}
+                          "1.0", products="gecko", animatable=False,
+                          spec="https://www.w3.org/TR/SVG/filters.html#FloodOpacityProperty")}
 
 ${helpers.predefined_type(
     "lighting-color", "CSSColor",
     "CSSParserColor::RGBA(RGBA { red: 1.0, green: 1.0, blue: 1.0, alpha: 1.0 })",
     products="gecko",
-    animatable=False)}
+    animatable=False,
+    spec="https://www.w3.org/TR/SVG/filters.html#LightingColorProperty")}
 
 // CSS Masking Module Level 1
-// https://www.w3.org/TR/css-masking-1/
+// https://drafts.fxtf.org/css-masking
 ${helpers.single_keyword("mask-type", "luminance alpha",
-                         products="gecko", animatable=False)}
+                         products="gecko", animatable=False,
+                         spec="https://drafts.fxtf.org/css-masking/#propdef-mask-type")}
 
-<%helpers:longhand name="clip-path" animatable="False" products="gecko">
+<%helpers:longhand name="clip-path" animatable="False" products="gecko"
+                   spec="https://drafts.fxtf.org/css-masking/#propdef-clip-path">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -81,7 +90,8 @@ ${helpers.single_keyword("mask-mode",
                          "alpha luminance match-source",
                          vector=True,
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.fxtf.org/css-masking/#propdef-mask-mode")}
 
 // TODO implement all of repeat-style for background and mask
 // https://drafts.csswg.org/css-backgrounds-3/#repeat-style
@@ -89,9 +99,11 @@ ${helpers.single_keyword("mask-repeat",
                          "repeat repeat-x repeat-y space round no-repeat",
                          vector=True,
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.fxtf.org/css-masking/#propdef-mask-repeat")}
 
-<%helpers:vector_longhand name="mask-position" products="gecko" animatable="True">
+<%helpers:vector_longhand name="mask-position" products="gecko" animatable="True"
+                          spec="https://drafts.fxtf.org/css-masking/#propdef-mask-position">
     use std::fmt;
     use style_traits::ToCss;
     use values::HasViewportPercentage;
@@ -151,7 +163,8 @@ ${helpers.single_keyword("mask-clip",
                          "content-box padding-box border-box",
                          vector=True,
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.fxtf.org/css-masking/#propdef-mask-clip")}
 
 // missing: margin-box fill-box stroke-box view-box
 // (gecko doesn't implement these)
@@ -159,9 +172,11 @@ ${helpers.single_keyword("mask-origin",
                          "content-box padding-box border-box",
                          vector=True,
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.fxtf.org/css-masking/#propdef-mask-origin")}
 
-<%helpers:longhand name="mask-size" products="gecko" animatable="True">
+<%helpers:longhand name="mask-size" products="gecko" animatable="True"
+                   spec="https://drafts.fxtf.org/css-masking/#propdef-mask-size">
     use properties::longhands::background_size;
     pub use ::properties::longhands::background_size::SpecifiedValue;
     pub use ::properties::longhands::background_size::single_value as single_value;
@@ -181,10 +196,12 @@ ${helpers.single_keyword("mask-composite",
                          "add subtract intersect exclude",
                          vector=True,
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.fxtf.org/css-masking/#propdef-mask-composite")}
 
 <%helpers:vector_longhand name="mask-image" products="gecko" animatable="False"
-                          has_uncacheable_values="${product == 'gecko'}">
+                          has_uncacheable_values="${product == 'gecko'}",
+                          spec="https://drafts.fxtf.org/css-masking/#propdef-mask-image">
     use std::fmt;
     use style_traits::ToCss;
     use std::sync::Arc;
diff --git a/components/style/properties/longhand/table.mako.rs b/components/style/properties/longhand/table.mako.rs
index a83d25c7c29..36e2216ef62 100644
--- a/components/style/properties/longhand/table.mako.rs
+++ b/components/style/properties/longhand/table.mako.rs
@@ -7,4 +7,5 @@
 <% data.new_style_struct("Table", inherited=False) %>
 
 ${helpers.single_keyword("table-layout", "auto fixed",
-                         gecko_ffi_name="mLayoutStrategy", animatable=False)}
+                         gecko_ffi_name="mLayoutStrategy", animatable=False,
+                         spec="https://drafts.csswg.org/css-tables/#propdef-table-layout")}
diff --git a/components/style/properties/longhand/text.mako.rs b/components/style/properties/longhand/text.mako.rs
index 541c8e13e04..912c55d98ff 100644
--- a/components/style/properties/longhand/text.mako.rs
+++ b/components/style/properties/longhand/text.mako.rs
@@ -12,7 +12,8 @@
                                              Method("has_overline", "bool"),
                                              Method("has_line_through", "bool")]) %>
 
-<%helpers:longhand name="text-overflow" animatable="False">
+<%helpers:longhand name="text-overflow" animatable="False"
+                   spec="https://drafts.csswg.org/css-ui/#propdef-text-overflow">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -93,13 +94,15 @@
 
 ${helpers.single_keyword("unicode-bidi",
                          "normal embed isolate bidi-override isolate-override plaintext",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-writing-modes/#propdef-unicode-bidi")}
 
 // FIXME: This prop should be animatable.
 <%helpers:longhand name="${'text-decoration' if product == 'servo' else 'text-decoration-line'}"
                    custom_cascade="${product == 'servo'}"
                    animatable="False"
-                   disable_when_testing="True">
+                   disable_when_testing="True",
+                   spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration-line">
     use std::fmt;
     use style_traits::ToCss;
     use values::NoViewportPercentage;
@@ -200,11 +203,13 @@ ${helpers.single_keyword("unicode-bidi",
 ${helpers.single_keyword("text-decoration-style",
                          "solid double dotted dashed wavy -moz-none",
                          products="gecko",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration-style")}
 
 ${helpers.predefined_type(
     "text-decoration-color", "CSSColor",
     "CSSParserColor::RGBA(RGBA { red: 0.0, green: 0.0, blue: 0.0, alpha: 1.0 })",
     complex_color=True,
     products="gecko",
-    animatable=True)}
+    animatable=True,
+    spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration-color")}
diff --git a/components/style/properties/longhand/ui.mako.rs b/components/style/properties/longhand/ui.mako.rs
index cd537677f6f..045627e004c 100644
--- a/components/style/properties/longhand/ui.mako.rs
+++ b/components/style/properties/longhand/ui.mako.rs
@@ -9,12 +9,16 @@
 // https://drafts.csswg.org/css-ui-3/
 <% data.new_style_struct("UI", inherited=False, gecko_name="UIReset") %>
 
+// TODO spec says that UAs should not support this
+// we should probably remove from gecko (https://bugzilla.mozilla.org/show_bug.cgi?id=1328331)
 ${helpers.single_keyword("ime-mode", "normal auto active disabled inactive",
                          products="gecko", gecko_ffi_name="mIMEMode",
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-ui/#input-method-editor")}
 
 ${helpers.single_keyword("-moz-user-select", "auto text none all", products="gecko",
                          gecko_ffi_name="mUserSelect",
                          gecko_enum_prefix="StyleUserSelect",
                          gecko_inexhaustive=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="https://drafts.csswg.org/css-ui-4/#propdef-user-select")}
diff --git a/components/style/properties/longhand/xul.mako.rs b/components/style/properties/longhand/xul.mako.rs
index bc64308a115..124e141f6ce 100644
--- a/components/style/properties/longhand/xul.mako.rs
+++ b/components/style/properties/longhand/xul.mako.rs
@@ -12,9 +12,11 @@ ${helpers.single_keyword("-moz-box-align", "stretch start center baseline end",
                          products="gecko", gecko_ffi_name="mBoxAlign",
                          gecko_enum_prefix="StyleBoxAlign",
                          gecko_inexhaustive=True,
-                         animatable=False)}
+                         animatable=False,
+                         spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/box-align)")}
 
 ${helpers.predefined_type("-moz-box-flex", "Number", "0.0", "parse_non_negative",
                           products="gecko", gecko_ffi_name="mBoxFlex",
                           needs_context=False,
-                          animatable=False)}
+                          animatable=False,
+                          spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/box-flex)")}
diff --git a/components/style/properties/properties.mako.rs b/components/style/properties/properties.mako.rs
index 75ea5dff3d5..647a5e7539d 100644
--- a/components/style/properties/properties.mako.rs
+++ b/components/style/properties/properties.mako.rs
@@ -1891,7 +1891,7 @@ pub fn apply_declarations<'a, F, I>(viewport_size: Size2D<Au>,
     let positioned = matches!(style.get_box().clone_position(),
         longhands::position::SpecifiedValue::absolute |
         longhands::position::SpecifiedValue::fixed);
-    let floated = style.get_box().clone_float() != longhands::float::SpecifiedValue::none;
+    let floated = style.get_box().clone_float() != longhands::float::computed_value::T::none;
     // FIXME(heycam): We should look past any display:contents ancestors to
     // determine if we are a flex or grid item, but we don't have access to
     // grandparent or higher style here.
diff --git a/components/style/properties/shorthand/background.mako.rs b/components/style/properties/shorthand/background.mako.rs
index d6ba7da83b8..857a728a7bb 100644
--- a/components/style/properties/shorthand/background.mako.rs
+++ b/components/style/properties/shorthand/background.mako.rs
@@ -8,7 +8,8 @@
 <%helpers:shorthand name="background"
                     sub_properties="background-color background-position-x background-position-y background-repeat
                                     background-attachment background-image background-size background-origin
-                                    background-clip">
+                                    background-clip"
+                    spec="https://drafts.csswg.org/css-backgrounds/#the-background">
     use properties::longhands::{background_color, background_position_x, background_position_y, background_repeat};
     use properties::longhands::{background_attachment, background_image, background_size, background_origin};
     use properties::longhands::background_clip;
@@ -252,7 +253,8 @@
 </%helpers:shorthand>
 
 <%helpers:shorthand name="background-position"
-                    sub_properties="background-position-x background-position-y">
+                    sub_properties="background-position-x background-position-y"
+                    spec="https://drafts.csswg.org/css-backgrounds-4/#the-background-position">
     use properties::longhands::{background_position_x,background_position_y};
     use values::specified::position::Position;
     use parser::Parse;
diff --git a/components/style/properties/shorthand/border.mako.rs b/components/style/properties/shorthand/border.mako.rs
index e324e690c70..19f33710b82 100644
--- a/components/style/properties/shorthand/border.mako.rs
+++ b/components/style/properties/shorthand/border.mako.rs
@@ -5,15 +5,18 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 <% from data import to_rust_ident, ALL_SIDES %>
 
-${helpers.four_sides_shorthand("border-color", "border-%s-color", "specified::CSSColor::parse")}
+${helpers.four_sides_shorthand("border-color", "border-%s-color", "specified::CSSColor::parse",
+                               spec="https://drafts.csswg.org/css-backgrounds/#border-color")}
 
 ${helpers.four_sides_shorthand("border-style", "border-%s-style",
                                "specified::BorderStyle::parse",
-                               needs_context=False)}
+                               needs_context=False,
+                               spec="https://drafts.csswg.org/css-backgrounds/#border-style")}
 
 <%helpers:shorthand name="border-width" sub_properties="${
         ' '.join('border-%s-width' % side
-                 for side in ['top', 'right', 'bottom', 'left'])}">
+                 for side in ['top', 'right', 'bottom', 'left'])}"
+    spec="https://drafts.csswg.org/css-backgrounds/#border-width">
     use super::parse_four_sides;
     use parser::Parse;
     use values::specified;
@@ -87,11 +90,16 @@ pub fn parse_border(context: &ParserContext, input: &mut Parser)
     if any { Ok((color, style, width)) } else { Err(()) }
 }
 
-% for side in map(lambda x: x[0], ALL_SIDES):
+% for side, logical in ALL_SIDES:
+    <%
+        spec = "https://drafts.csswg.org/css-backgrounds/#border-%s" % side
+        if logical:
+            spec = "https://drafts.csswg.org/css-logical-props/#propdef-border-%s" % side
+    %>
     <%helpers:shorthand name="border-${side}" sub_properties="${' '.join(
         'border-%s-%s' % (side, prop)
         for prop in ['color', 'style', 'width']
-    )}">
+    )}" spec="${spec}">
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
         let (color, style, width) = try!(super::parse_border(context, input));
@@ -120,7 +128,7 @@ pub fn parse_border(context: &ParserContext, input: &mut Parser)
     'border-%s-%s' % (side, prop)
     for side in ['top', 'right', 'bottom', 'left']
     for prop in ['color', 'style', 'width']
-)}">
+)}" spec="https://drafts.csswg.org/css-backgrounds/#border">
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
         let (color, style, width) = try!(super::parse_border(context, input));
@@ -151,7 +159,7 @@ pub fn parse_border(context: &ParserContext, input: &mut Parser)
 <%helpers:shorthand name="border-radius" sub_properties="${' '.join(
     'border-%s-radius' % (corner)
      for corner in ['top-left', 'top-right', 'bottom-right', 'bottom-left']
-)}">
+)}" spec="https://drafts.csswg.org/css-backgrounds/#border-radius">
     use values::specified::basic_shape::BorderRadius;
     use parser::Parse;
 
@@ -184,9 +192,9 @@ pub fn parse_border(context: &ParserContext, input: &mut Parser)
     }
 </%helpers:shorthand>
 
-// https://drafts.csswg.org/css-backgrounds-3/#border-image
 <%helpers:shorthand name="border-image" products="gecko" sub_properties="border-image-outset
-    border-image-repeat border-image-slice border-image-source border-image-width">
+    border-image-repeat border-image-slice border-image-source border-image-width"
+    spec="https://drafts.csswg.org/css-backgrounds-3/#border-image">
     use properties::longhands::{border_image_outset, border_image_repeat, border_image_slice};
     use properties::longhands::{border_image_source, border_image_width};
 
diff --git a/components/style/properties/shorthand/box.mako.rs b/components/style/properties/shorthand/box.mako.rs
index 836eade0234..c836fe3a01b 100644
--- a/components/style/properties/shorthand/box.mako.rs
+++ b/components/style/properties/shorthand/box.mako.rs
@@ -4,7 +4,8 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<%helpers:shorthand name="overflow" sub_properties="overflow-x overflow-y">
+<%helpers:shorthand name="overflow" sub_properties="overflow-x overflow-y"
+                    spec="https://drafts.csswg.org/css-overflow/#propdef-overflow">
     use properties::longhands::{overflow_x, overflow_y};
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
@@ -96,7 +97,8 @@ macro_rules! try_parse_one {
 <%helpers:shorthand name="transition"
                     sub_properties="transition-property transition-duration
                                     transition-timing-function
-                                    transition-delay">
+                                    transition-delay"
+                    spec="https://drafts.csswg.org/css-transitions/#propdef-transition">
     use parser::Parse;
     use properties::longhands::{transition_delay, transition_duration, transition_property};
     use properties::longhands::{transition_timing_function};
@@ -185,7 +187,8 @@ macro_rules! try_parse_one {
                                     animation-timing-function animation-delay
                                     animation-iteration-count animation-direction
                                     animation-fill-mode animation-play-state"
-                    allowed_in_keyframe_block="False">
+                    allowed_in_keyframe_block="False"
+                    spec="https://drafts.csswg.org/css-animations/#propdef-animation">
     use parser::Parse;
     use properties::longhands::{animation_name, animation_duration, animation_timing_function};
     use properties::longhands::{animation_delay, animation_iteration_count, animation_direction};
@@ -332,7 +335,8 @@ macro_rules! try_parse_one {
 </%helpers:shorthand>
 
 <%helpers:shorthand name="scroll-snap-type" products="gecko"
-                    sub_properties="scroll-snap-type-x scroll-snap-type-y">
+                    sub_properties="scroll-snap-type-x scroll-snap-type-y"
+                    spec="https://drafts.csswg.org/css-scroll-snap/#propdef-scroll-snap-type">
     use properties::longhands::scroll_snap_type_x;
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
diff --git a/components/style/properties/shorthand/column.mako.rs b/components/style/properties/shorthand/column.mako.rs
index e2b6f2ac5a7..69aa6baeeb6 100644
--- a/components/style/properties/shorthand/column.mako.rs
+++ b/components/style/properties/shorthand/column.mako.rs
@@ -4,7 +4,8 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<%helpers:shorthand name="columns" sub_properties="column-count column-width" experimental="True">
+<%helpers:shorthand name="columns" sub_properties="column-count column-width" experimental="True"
+                    spec="https://drafts.csswg.org/css-multicol/#propdef-columns">
     use properties::longhands::{column_count, column_width};
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
@@ -58,9 +59,9 @@
     }
 </%helpers:shorthand>
 
-// https://drafts.csswg.org/css-multicol/#column-rule
 <%helpers:shorthand name="column-rule" products="gecko"
-    sub_properties="column-rule-width column-rule-style column-rule-color">
+    sub_properties="column-rule-width column-rule-style column-rule-color"
+    spec="https://drafts.csswg.org/css-multicol/#propdef-column-rule">
     use properties::longhands::{column_rule_width, column_rule_style};
     use properties::longhands::column_rule_color;
 
diff --git a/components/style/properties/shorthand/font.mako.rs b/components/style/properties/shorthand/font.mako.rs
index 555b098e575..7742ab11be5 100644
--- a/components/style/properties/shorthand/font.mako.rs
+++ b/components/style/properties/shorthand/font.mako.rs
@@ -5,7 +5,8 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="font" sub_properties="font-style font-variant font-weight
-                                                font-size line-height font-family">
+                                                font-size line-height font-family"
+                    spec="https://drafts.csswg.org/css-fonts-3/#propdef-font">
     use properties::longhands::{font_style, font_variant, font_weight, font_size,
                                 line_height, font_family};
 
diff --git a/components/style/properties/shorthand/inherited_text.mako.rs b/components/style/properties/shorthand/inherited_text.mako.rs
index ba2c49423bd..fe5fe298f49 100644
--- a/components/style/properties/shorthand/inherited_text.mako.rs
+++ b/components/style/properties/shorthand/inherited_text.mako.rs
@@ -6,7 +6,8 @@
 
 // Per CSS-TEXT 6.2, "for legacy reasons, UAs must treat `word-wrap` as an alternate name for
 // the `overflow-wrap` property, as if it were a shorthand of `overflow-wrap`."
-<%helpers:shorthand name="word-wrap" sub_properties="overflow-wrap">
+<%helpers:shorthand name="word-wrap" sub_properties="overflow-wrap"
+                    spec="https://drafts.csswg.org/css-text/#propdef-word-wrap">
     use properties::longhands::overflow_wrap;
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
@@ -22,9 +23,9 @@
     }
 </%helpers:shorthand>
 
-// https://drafts.csswg.org/css-text-decor-3/#text-emphasis-property
 <%helpers:shorthand name="text-emphasis" products="gecko" sub_properties="text-emphasis-color
-    text-emphasis-style">
+    text-emphasis-style"
+    spec="https://drafts.csswg.org/css-text-decor-3/#text-emphasis-property">
     use properties::longhands::{text_emphasis_color, text_emphasis_style};
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
@@ -80,11 +81,12 @@
 </%helpers:shorthand>
 
 // CSS Compatibility
-// https://compat.spec.whatwg.org/#the-webkit-text-stroke
+// https://compat.spec.whatwg.org/
 <%helpers:shorthand name="-webkit-text-stroke"
                     sub_properties="-webkit-text-stroke-color
                                     -webkit-text-stroke-width"
-                    products="gecko">
+                    products="gecko"
+                    spec="https://compat.spec.whatwg.org/#the-webkit-text-stroke">
     use cssparser::Color as CSSParserColor;
     use properties::longhands::{_webkit_text_stroke_color, _webkit_text_stroke_width};
     use values::specified::CSSColor;
diff --git a/components/style/properties/shorthand/list.mako.rs b/components/style/properties/shorthand/list.mako.rs
index f425c71c9f7..95b27da2a81 100644
--- a/components/style/properties/shorthand/list.mako.rs
+++ b/components/style/properties/shorthand/list.mako.rs
@@ -5,7 +5,8 @@
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
 <%helpers:shorthand name="list-style"
-                    sub_properties="list-style-image list-style-position list-style-type">
+                    sub_properties="list-style-image list-style-position list-style-type"
+                    spec="https://drafts.csswg.org/css-lists/#propdef-list-style">
     use properties::longhands::{list_style_image, list_style_position, list_style_type};
     use values::{Either, None_};
 
diff --git a/components/style/properties/shorthand/margin.mako.rs b/components/style/properties/shorthand/margin.mako.rs
index f83ccb54023..c8e11a8710d 100644
--- a/components/style/properties/shorthand/margin.mako.rs
+++ b/components/style/properties/shorthand/margin.mako.rs
@@ -4,4 +4,5 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-${helpers.four_sides_shorthand("margin", "margin-%s", "specified::LengthOrPercentageOrAuto::parse")}
+${helpers.four_sides_shorthand("margin", "margin-%s", "specified::LengthOrPercentageOrAuto::parse",
+                               spec="https://drafts.csswg.org/css-box/#propdef-margin")}
diff --git a/components/style/properties/shorthand/mask.mako.rs b/components/style/properties/shorthand/mask.mako.rs
index 67e1386f6d6..f4d3ae6d5bc 100644
--- a/components/style/properties/shorthand/mask.mako.rs
+++ b/components/style/properties/shorthand/mask.mako.rs
@@ -6,7 +6,8 @@
 
 <%helpers:shorthand name="mask" products="gecko"
                     sub_properties="mask-mode mask-repeat mask-clip mask-origin mask-composite mask-position
-                                    mask-size mask-image">
+                                    mask-size mask-image"
+                    spec="https://drafts.fxtf.org/css-masking/#propdef-mask">
     use properties::longhands::{mask_mode, mask_repeat, mask_clip, mask_origin, mask_composite, mask_position};
     use properties::longhands::{mask_size, mask_image};
 
diff --git a/components/style/properties/shorthand/outline.mako.rs b/components/style/properties/shorthand/outline.mako.rs
index 51d74018124..2fa406e3fca 100644
--- a/components/style/properties/shorthand/outline.mako.rs
+++ b/components/style/properties/shorthand/outline.mako.rs
@@ -4,7 +4,8 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-<%helpers:shorthand name="outline" sub_properties="outline-color outline-style outline-width">
+<%helpers:shorthand name="outline" sub_properties="outline-color outline-style outline-width"
+                    spec="https://drafts.csswg.org/css-ui/#propdef-outline">
     use properties::longhands::outline_width;
     use values::specified;
     use parser::Parse;
@@ -75,7 +76,7 @@
 <%helpers:shorthand name="-moz-outline-radius" sub_properties="${' '.join(
     '-moz-outline-radius-%s' % corner
     for corner in ['topleft', 'topright', 'bottomright', 'bottomleft']
-)}" products="gecko">
+)}" products="gecko" spec="Nonstandard (https://developer.mozilla.org/en-US/docs/Web/CSS/-moz-outline-radius)">
     use properties::shorthands;
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
diff --git a/components/style/properties/shorthand/padding.mako.rs b/components/style/properties/shorthand/padding.mako.rs
index 09363b950eb..a0e94f8bdcb 100644
--- a/components/style/properties/shorthand/padding.mako.rs
+++ b/components/style/properties/shorthand/padding.mako.rs
@@ -4,4 +4,5 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-${helpers.four_sides_shorthand("padding", "padding-%s", "specified::LengthOrPercentage::parse")}
+${helpers.four_sides_shorthand("padding", "padding-%s", "specified::LengthOrPercentage::parse",
+                               spec="https://drafts.csswg.org/css-box-3/#propdef-padding")}
diff --git a/components/style/properties/shorthand/position.mako.rs b/components/style/properties/shorthand/position.mako.rs
index 3865ac8042d..13e11a8ef3f 100644
--- a/components/style/properties/shorthand/position.mako.rs
+++ b/components/style/properties/shorthand/position.mako.rs
@@ -4,8 +4,8 @@
 
 <%namespace name="helpers" file="/helpers.mako.rs" />
 
-// https://drafts.csswg.org/css-flexbox/#flex-flow-property
-<%helpers:shorthand name="flex-flow" sub_properties="flex-direction flex-wrap">
+<%helpers:shorthand name="flex-flow" sub_properties="flex-direction flex-wrap"
+                    spec="https://drafts.csswg.org/css-flexbox/#flex-flow-property">
     use properties::longhands::{flex_direction, flex_wrap};
 
     pub fn parse_value(context: &ParserContext, input: &mut Parser) -> Result<Longhands, ()> {
@@ -54,8 +54,8 @@
     }
 </%helpers:shorthand>
 
-// https://drafts.csswg.org/css-flexbox/#flex-property
-<%helpers:shorthand name="flex" sub_properties="flex-grow flex-shrink flex-basis">
+<%helpers:shorthand name="flex" sub_properties="flex-grow flex-shrink flex-basis"
+                    spec="https://drafts.csswg.org/css-flexbox/#flex-property">
     use parser::Parse;
     use app_units::Au;
     use values::specified::{Number, Length, LengthOrPercentageOrAutoOrContent};
diff --git a/components/style/properties/shorthand/text.mako.rs b/components/style/properties/shorthand/text.mako.rs
index 0fc8ffec85e..24813d34d44 100644
--- a/components/style/properties/shorthand/text.mako.rs
+++ b/components/style/properties/shorthand/text.mako.rs
@@ -9,7 +9,8 @@
                                     text-decoration-line
                                     text-decoration-style"
                     products="gecko"
-                    disable_when_testing="True">
+                    disable_when_testing="True"
+                    spec="https://drafts.csswg.org/css-text-decor/#propdef-text-decoration">
     use cssparser::Color as CSSParserColor;
     use properties::longhands::{text_decoration_color, text_decoration_line, text_decoration_style};
     use values::specified::CSSColor;