diff --git a/servo/Cargo.lock b/servo/Cargo.lock
index 852654956254..07cc363059ab 100644
--- a/servo/Cargo.lock
+++ b/servo/Cargo.lock
@@ -2972,6 +2972,7 @@ name = "style_traits"
 version = "0.0.1"
 dependencies = [
  "app_units 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bitflags 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.14.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.13.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "heapsize 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
diff --git a/servo/components/script/dom/css.rs b/servo/components/script/dom/css.rs
index 66f522b23711..31ca219093e3 100644
--- a/servo/components/script/dom/css.rs
+++ b/servo/components/script/dom/css.rs
@@ -10,9 +10,10 @@ use dom::bindings::str::DOMString;
 use dom::window::Window;
 use dom_struct::dom_struct;
 use style::context::QuirksMode;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::stylesheets::CssRuleType;
 use style::stylesheets::supports_rule::{Declaration, parse_condition_or_declaration};
+use style_traits::PARSING_MODE_DEFAULT;
 
 #[dom_struct]
 pub struct CSS {
diff --git a/servo/components/script/dom/cssmediarule.rs b/servo/components/script/dom/cssmediarule.rs
index 1f5535f1b3ea..3c27127ecf4c 100644
--- a/servo/components/script/dom/cssmediarule.rs
+++ b/servo/components/script/dom/cssmediarule.rs
@@ -16,11 +16,11 @@ use dom::medialist::MediaList;
 use dom::window::Window;
 use dom_struct::dom_struct;
 use style::media_queries::parse_media_query_list;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylearc::Arc;
 use style::stylesheets::{CssRuleType, MediaRule};
-use style_traits::ToCss;
+use style_traits::{PARSING_MODE_DEFAULT, ToCss};
 
 #[dom_struct]
 pub struct CSSMediaRule {
diff --git a/servo/components/script/dom/cssstyledeclaration.rs b/servo/components/script/dom/cssstyledeclaration.rs
index 5def880aa7d9..2ef448720d67 100644
--- a/servo/components/script/dom/cssstyledeclaration.rs
+++ b/servo/components/script/dom/cssstyledeclaration.rs
@@ -17,13 +17,12 @@ use dom_struct::dom_struct;
 use servo_url::ServoUrl;
 use std::ascii::AsciiExt;
 use style::attr::AttrValue;
-use style::parser::PARSING_MODE_DEFAULT;
 use style::properties::{Importance, PropertyDeclarationBlock, PropertyId, LonghandId, ShorthandId};
 use style::properties::{parse_one_declaration_into, parse_style_attribute, SourcePropertyDeclaration};
 use style::selector_parser::PseudoElement;
 use style::shared_lock::Locked;
 use style::stylearc::Arc;
-use style_traits::ToCss;
+use style_traits::{PARSING_MODE_DEFAULT, ToCss};
 
 // http://dev.w3.org/csswg/cssom/#the-cssstyledeclaration-interface
 #[dom_struct]
diff --git a/servo/components/script/dom/csssupportsrule.rs b/servo/components/script/dom/csssupportsrule.rs
index 2897b47b35f1..73503d0dfa6a 100644
--- a/servo/components/script/dom/csssupportsrule.rs
+++ b/servo/components/script/dom/csssupportsrule.rs
@@ -13,12 +13,12 @@ use dom::cssrule::SpecificCSSRule;
 use dom::cssstylesheet::CSSStyleSheet;
 use dom::window::Window;
 use dom_struct::dom_struct;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::shared_lock::{Locked, ToCssWithGuard};
 use style::stylearc::Arc;
 use style::stylesheets::{CssRuleType, SupportsRule};
 use style::stylesheets::supports_rule::SupportsCondition;
-use style_traits::ToCss;
+use style_traits::{PARSING_MODE_DEFAULT, ToCss};
 
 #[dom_struct]
 pub struct CSSSupportsRule {
diff --git a/servo/components/script/dom/htmllinkelement.rs b/servo/components/script/dom/htmllinkelement.rs
index da004317179d..ff004261db5d 100644
--- a/servo/components/script/dom/htmllinkelement.rs
+++ b/servo/components/script/dom/htmllinkelement.rs
@@ -32,10 +32,11 @@ use std::cell::Cell;
 use std::default::Default;
 use style::attr::AttrValue;
 use style::media_queries::parse_media_query_list;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext as CssParserContext};
+use style::parser::ParserContext as CssParserContext;
 use style::str::HTML_SPACE_CHARACTERS;
 use style::stylearc::Arc;
 use style::stylesheets::{CssRuleType, Stylesheet};
+use style_traits::PARSING_MODE_DEFAULT;
 use stylesheet_loader::{StylesheetLoader, StylesheetContextSource, StylesheetOwner};
 
 unsafe_no_jsmanaged_fields!(Stylesheet);
diff --git a/servo/components/script/dom/htmlstyleelement.rs b/servo/components/script/dom/htmlstyleelement.rs
index 4067cb7439d4..bf4266e18750 100644
--- a/servo/components/script/dom/htmlstyleelement.rs
+++ b/servo/components/script/dom/htmlstyleelement.rs
@@ -23,9 +23,10 @@ use net_traits::ReferrerPolicy;
 use script_layout_interface::message::Msg;
 use std::cell::Cell;
 use style::media_queries::parse_media_query_list;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext as CssParserContext};
+use style::parser::ParserContext as CssParserContext;
 use style::stylearc::Arc;
 use style::stylesheets::{CssRuleType, Stylesheet, Origin};
+use style_traits::PARSING_MODE_DEFAULT;
 use stylesheet_loader::{StylesheetLoader, StylesheetOwner};
 
 #[dom_struct]
diff --git a/servo/components/script/dom/medialist.rs b/servo/components/script/dom/medialist.rs
index d77af9dc1b95..55ca57cb4fdb 100644
--- a/servo/components/script/dom/medialist.rs
+++ b/servo/components/script/dom/medialist.rs
@@ -14,11 +14,11 @@ use dom::window::Window;
 use dom_struct::dom_struct;
 use style::media_queries::{MediaQuery, parse_media_query_list};
 use style::media_queries::MediaList as StyleMediaList;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::shared_lock::{SharedRwLock, Locked};
 use style::stylearc::Arc;
 use style::stylesheets::CssRuleType;
-use style_traits::ToCss;
+use style_traits::{PARSING_MODE_DEFAULT, ToCss};
 
 #[dom_struct]
 pub struct MediaList {
diff --git a/servo/components/script/dom/window.rs b/servo/components/script/dom/window.rs
index 6e89024887ab..c4ec3c07248f 100644
--- a/servo/components/script/dom/window.rs
+++ b/servo/components/script/dom/window.rs
@@ -107,12 +107,13 @@ use std::sync::mpsc::TryRecvError::{Disconnected, Empty};
 use style::context::ReflowGoal;
 use style::error_reporting::ParseErrorReporter;
 use style::media_queries;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext as CssParserContext};
+use style::parser::ParserContext as CssParserContext;
 use style::properties::PropertyId;
 use style::properties::longhands::overflow_x;
 use style::selector_parser::PseudoElement;
 use style::str::HTML_SPACE_CHARACTERS;
 use style::stylesheets::CssRuleType;
+use style_traits::PARSING_MODE_DEFAULT;
 use task_source::dom_manipulation::DOMManipulationTaskSource;
 use task_source::file_reading::FileReadingTaskSource;
 use task_source::history_traversal::HistoryTraversalTaskSource;
diff --git a/servo/components/style/parser.rs b/servo/components/style/parser.rs
index 420572042da6..0145c128eca3 100644
--- a/servo/components/style/parser.rs
+++ b/servo/components/style/parser.rs
@@ -7,37 +7,11 @@
 use context::QuirksMode;
 use cssparser::{Parser, SourcePosition, UnicodeRange};
 use error_reporting::{ParseErrorReporter, ContextualParseError};
-use style_traits::{OneOrMoreCommaSeparated, ParseError};
+use style_traits::{OneOrMoreCommaSeparated, ParseError, ParsingMode};
+#[cfg(feature = "gecko")]
+use style_traits::{PARSING_MODE_DEFAULT, PARSING_MODE_ALLOW_UNITLESS_LENGTH, PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES};
 use stylesheets::{CssRuleType, Origin, UrlExtraData, Namespaces};
 
-bitflags! {
-    /// The mode to use when parsing values.
-    pub flags ParsingMode: u8 {
-        /// In CSS, lengths must have units, except for zero values, where the unit can be omitted.
-        /// https://www.w3.org/TR/css3-values/#lengths
-        const PARSING_MODE_DEFAULT = 0x00,
-        /// In SVG, a coordinate or length value without a unit identifier (e.g., "25") is assumed
-        /// to be in user units (px).
-        /// https://www.w3.org/TR/SVG/coords.html#Units
-        const PARSING_MODE_ALLOW_UNITLESS_LENGTH = 0x01,
-        /// In SVG, out-of-range values are not treated as an error in parsing.
-        /// https://www.w3.org/TR/SVG/implnote.html#RangeClamping
-        const PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES = 0x02,
-    }
-}
-
-impl ParsingMode {
-    /// Whether the parsing mode allows unitless lengths for non-zero values to be intpreted as px.
-    pub fn allows_unitless_lengths(&self) -> bool {
-        self.intersects(PARSING_MODE_ALLOW_UNITLESS_LENGTH)
-    }
-
-    /// Whether the parsing mode allows all numeric values.
-    pub fn allows_all_numeric_values(&self) -> bool {
-      self.intersects(PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES)
-    }
-}
-
 /// Asserts that all ParsingMode flags have a matching ParsingMode value in gecko.
 #[cfg(feature = "gecko")]
 #[inline]
diff --git a/servo/components/style/properties/declaration_block.rs b/servo/components/style/properties/declaration_block.rs
index 3c36521ba615..0cc0aeca2fc3 100644
--- a/servo/components/style/properties/declaration_block.rs
+++ b/servo/components/style/properties/declaration_block.rs
@@ -10,13 +10,13 @@ use context::QuirksMode;
 use cssparser::{DeclarationListParser, parse_important, ParserInput};
 use cssparser::{Parser, AtRuleParser, DeclarationParser, Delimiter};
 use error_reporting::{ParseErrorReporter, ContextualParseError};
-use parser::{PARSING_MODE_DEFAULT, ParsingMode, ParserContext, log_css_error};
+use parser::{ParserContext, log_css_error};
 use properties::animated_properties::AnimationValue;
 use selectors::parser::SelectorParseError;
 use shared_lock::Locked;
 use std::fmt;
 use std::slice::Iter;
-use style_traits::{ToCss, ParseError, StyleParseError};
+use style_traits::{PARSING_MODE_DEFAULT, ToCss, ParseError, ParsingMode, StyleParseError};
 use stylesheets::{CssRuleType, Origin, UrlExtraData};
 use stylesheets::{MallocSizeOf, MallocSizeOfFn};
 use super::*;
diff --git a/servo/components/style/properties/properties.mako.rs b/servo/components/style/properties/properties.mako.rs
index 8bd5ec4680d9..44d0d55a1c3d 100644
--- a/servo/components/style/properties/properties.mako.rs
+++ b/servo/components/style/properties/properties.mako.rs
@@ -31,13 +31,13 @@ use font_metrics::FontMetricsProvider;
 #[cfg(feature = "servo")] use logical_geometry::{LogicalMargin, PhysicalSide};
 use logical_geometry::WritingMode;
 use media_queries::Device;
-use parser::{PARSING_MODE_DEFAULT, Parse, ParserContext};
+use parser::{Parse, ParserContext};
 use properties::animated_properties::TransitionProperty;
 #[cfg(feature = "gecko")] use properties::longhands::system_font::SystemFont;
 use selectors::parser::SelectorParseError;
 #[cfg(feature = "servo")] use servo_config::prefs::PREFS;
 use shared_lock::StylesheetGuards;
-use style_traits::{HasViewportPercentage, ToCss, ParseError, PropertyDeclarationParseError};
+use style_traits::{PARSING_MODE_DEFAULT, HasViewportPercentage, ToCss, ParseError, PropertyDeclarationParseError};
 use stylesheets::{CssRuleType, MallocSizeOf, MallocSizeOfFn, Origin, UrlExtraData};
 #[cfg(feature = "servo")] use values::Either;
 use values::generics::text::LineHeight;
diff --git a/servo/components/style/stylesheets/keyframes_rule.rs b/servo/components/style/stylesheets/keyframes_rule.rs
index c87477a617bf..c03240ecafc0 100644
--- a/servo/components/style/stylesheets/keyframes_rule.rs
+++ b/servo/components/style/stylesheets/keyframes_rule.rs
@@ -7,7 +7,7 @@
 use cssparser::{AtRuleParser, Parser, QualifiedRuleParser, RuleListParser, ParserInput};
 use cssparser::{DeclarationListParser, DeclarationParser, parse_one_rule, SourceLocation};
 use error_reporting::{NullReporter, ContextualParseError};
-use parser::{PARSING_MODE_DEFAULT, ParserContext, log_css_error};
+use parser::{ParserContext, log_css_error};
 use properties::{Importance, PropertyDeclaration, PropertyDeclarationBlock, PropertyId};
 use properties::{PropertyDeclarationId, LonghandId, SourcePropertyDeclaration};
 use properties::LonghandIdSet;
@@ -17,7 +17,7 @@ use selectors::parser::SelectorParseError;
 use shared_lock::{DeepCloneWithLock, SharedRwLock, SharedRwLockReadGuard, Locked, ToCssWithGuard};
 use std::borrow::Cow;
 use std::fmt;
-use style_traits::{ToCss, ParseError, StyleParseError};
+use style_traits::{PARSING_MODE_DEFAULT, ToCss, ParseError, StyleParseError};
 use stylearc::Arc;
 use stylesheets::{CssRuleType, Stylesheet};
 use stylesheets::rule_parser::VendorPrefix;
diff --git a/servo/components/style/stylesheets/mod.rs b/servo/components/style/stylesheets/mod.rs
index 67354889b933..e5e6aa521f9f 100644
--- a/servo/components/style/stylesheets/mod.rs
+++ b/servo/components/style/stylesheets/mod.rs
@@ -24,9 +24,10 @@ pub mod viewport_rule;
 
 use cssparser::{parse_one_rule, Parser, ParserInput};
 use error_reporting::NullReporter;
-use parser::{ParserContext, PARSING_MODE_DEFAULT};
+use parser::ParserContext;
 use shared_lock::{DeepCloneWithLock, Locked, SharedRwLock, SharedRwLockReadGuard, ToCssWithGuard};
 use std::fmt;
+use style_traits::PARSING_MODE_DEFAULT;
 use stylearc::Arc;
 
 pub use self::counter_style_rule::CounterStyleRule;
diff --git a/servo/components/style/stylesheets/stylesheet.rs b/servo/components/style/stylesheets/stylesheet.rs
index db49e109687d..477c35f8e641 100644
--- a/servo/components/style/stylesheets/stylesheet.rs
+++ b/servo/components/style/stylesheets/stylesheet.rs
@@ -9,10 +9,11 @@ use error_reporting::{ParseErrorReporter, ContextualParseError};
 use fnv::FnvHashMap;
 use media_queries::{MediaList, Device};
 use parking_lot::RwLock;
-use parser::{PARSING_MODE_DEFAULT, ParserContext, log_css_error};
+use parser::{ParserContext, log_css_error};
 use shared_lock::{DeepCloneWithLock, Locked, SharedRwLock, SharedRwLockReadGuard};
 use std::mem;
 use std::sync::atomic::{AtomicBool, Ordering};
+use style_traits::PARSING_MODE_DEFAULT;
 use stylearc::Arc;
 use stylesheets::{CssRule, CssRules, Origin, UrlExtraData};
 use stylesheets::loader::StylesheetLoader;
diff --git a/servo/components/style/values/specified/length.rs b/servo/components/style/values/specified/length.rs
index d2e6e45d4071..a2662247d6f7 100644
--- a/servo/components/style/values/specified/length.rs
+++ b/servo/components/style/values/specified/length.rs
@@ -611,9 +611,9 @@ impl Length {
                               -> Result<Length, ParseError<'i>> {
         let token = try!(input.next());
         match token {
-            Token::Dimension(ref value, ref unit) if num_context.is_ok(value.value) =>
+            Token::Dimension(ref value, ref unit) if num_context.is_ok(context.parsing_mode, value.value) =>
                 Length::parse_dimension(context, value.value, unit),
-            Token::Number(ref value) if num_context.is_ok(value.value) => {
+            Token::Number(ref value) if num_context.is_ok(context.parsing_mode, value.value) => {
                 if value.value != 0. &&
                    !context.parsing_mode.allows_unitless_lengths() &&
                    !allow_quirks.allowed(context.quirks_mode) {
@@ -715,11 +715,12 @@ impl ToCss for Percentage {
 
 impl Percentage {
     /// Parse a specific kind of percentage.
-    pub fn parse_with_clamping_mode<'i, 't>(input: &mut Parser<'i, 't>,
-                                            context: AllowedNumericType)
+    pub fn parse_with_clamping_mode<'i, 't>(context: &ParserContext,
+                                            input: &mut Parser<'i, 't>,
+                                            num_context: AllowedNumericType)
                                             -> Result<Self, ParseError<'i>> {
         match try!(input.next()) {
-            Token::Percentage(ref value) if context.is_ok(value.unit_value) => {
+            Token::Percentage(ref value) if num_context.is_ok(context.parsing_mode, value.unit_value) => {
                 Ok(Percentage(value.unit_value))
             }
             t => Err(BasicParseError::UnexpectedToken(t).into())
@@ -727,8 +728,10 @@ impl Percentage {
     }
 
     /// Parses a percentage token, but rejects it if it's negative.
-    pub fn parse_non_negative<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
-        Self::parse_with_clamping_mode(input, AllowedNumericType::NonNegative)
+    pub fn parse_non_negative<'i, 't>(context: &ParserContext,
+                                      input: &mut Parser<'i, 't>)
+                                      -> Result<Self, ParseError<'i>> {
+        Self::parse_with_clamping_mode(context, input, AllowedNumericType::NonNegative)
     }
 
     /// 0%
@@ -746,8 +749,8 @@ impl Percentage {
 
 impl Parse for Percentage {
     #[inline]
-    fn parse<'i, 't>(_context: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
-        Self::parse_with_clamping_mode(input, AllowedNumericType::All)
+    fn parse<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>) -> Result<Self, ParseError<'i>> {
+        Self::parse_with_clamping_mode(context, input, AllowedNumericType::All)
     }
 }
 
@@ -801,11 +804,11 @@ impl LengthOrPercentage {
     {
         let token = try!(input.next());
         match token {
-            Token::Dimension(ref value, ref unit) if num_context.is_ok(value.value) =>
+            Token::Dimension(ref value, ref unit) if num_context.is_ok(context.parsing_mode, value.value) =>
                 NoCalcLength::parse_dimension(context, value.value, unit).map(LengthOrPercentage::Length),
-            Token::Percentage(ref value) if num_context.is_ok(value.unit_value) =>
+            Token::Percentage(ref value) if num_context.is_ok(context.parsing_mode, value.unit_value) =>
                 return Ok(LengthOrPercentage::Percentage(Percentage(value.unit_value))),
-            Token::Number(value) if num_context.is_ok(value.value) => {
+            Token::Number(value) if num_context.is_ok(context.parsing_mode, value.value) => {
                 if value.value != 0. &&
                    !context.parsing_mode.allows_unitless_lengths() &&
                    !allow_quirks.allowed(context.quirks_mode) {
@@ -935,11 +938,11 @@ impl LengthOrPercentageOrAuto {
                               -> Result<Self, ParseError<'i>> {
         let token = try!(input.next());
         match token {
-            Token::Dimension(ref value, ref unit) if num_context.is_ok(value.value) =>
+            Token::Dimension(ref value, ref unit) if num_context.is_ok(context.parsing_mode, value.value) =>
                 NoCalcLength::parse_dimension(context, value.value, unit).map(LengthOrPercentageOrAuto::Length),
-            Token::Percentage(ref value) if num_context.is_ok(value.unit_value) =>
+            Token::Percentage(ref value) if num_context.is_ok(context.parsing_mode, value.unit_value) =>
                 Ok(LengthOrPercentageOrAuto::Percentage(Percentage(value.unit_value))),
-            Token::Number(ref value) if num_context.is_ok(value.value) => {
+            Token::Number(ref value) if num_context.is_ok(context.parsing_mode, value.value) => {
                 if value.value != 0. &&
                    !context.parsing_mode.allows_unitless_lengths() &&
                    !allow_quirks.allowed(context.quirks_mode) {
@@ -1031,11 +1034,11 @@ impl LengthOrPercentageOrNone {
     {
         let token = try!(input.next());
         match token {
-            Token::Dimension(ref value, ref unit) if num_context.is_ok(value.value) =>
+            Token::Dimension(ref value, ref unit) if num_context.is_ok(context.parsing_mode, value.value) =>
                 NoCalcLength::parse_dimension(context, value.value, unit).map(LengthOrPercentageOrNone::Length),
-            Token::Percentage(ref value) if num_context.is_ok(value.unit_value) =>
+            Token::Percentage(ref value) if num_context.is_ok(context.parsing_mode, value.unit_value) =>
                 Ok(LengthOrPercentageOrNone::Percentage(Percentage(value.unit_value))),
-            Token::Number(value) if num_context.is_ok(value.value) => {
+            Token::Number(value) if num_context.is_ok(context.parsing_mode, value.value) => {
                 if value.value != 0. && !context.parsing_mode.allows_unitless_lengths() &&
                    !allow_quirks.allowed(context.quirks_mode) {
                     return Err(StyleParseError::UnspecifiedError.into())
@@ -1113,10 +1116,10 @@ impl LengthOrPercentageOrAutoOrContent {
         let num_context = AllowedLengthType::NonNegative;
         let token = try!(input.next());
         match token {
-            Token::Dimension(ref value, ref unit) if num_context.is_ok(value.value) =>
+            Token::Dimension(ref value, ref unit) if num_context.is_ok(context.parsing_mode, value.value) =>
                 NoCalcLength::parse_dimension(context, value.value, unit)
                              .map(LengthOrPercentageOrAutoOrContent::Length),
-            Token::Percentage(ref value) if num_context.is_ok(value.unit_value) =>
+            Token::Percentage(ref value) if num_context.is_ok(context.parsing_mode, value.unit_value) =>
                 Ok(LengthOrPercentageOrAutoOrContent::Percentage(Percentage(value.unit_value))),
             Token::Number(ref value) if value.value == 0. =>
                 Ok(Self::zero()),
diff --git a/servo/components/style/values/specified/mod.rs b/servo/components/style/values/specified/mod.rs
index 80ce0db08d05..112a3c38bc65 100644
--- a/servo/components/style/values/specified/mod.rs
+++ b/servo/components/style/values/specified/mod.rs
@@ -120,7 +120,7 @@ pub fn parse_number_with_clamping_mode<'i, 't>(context: &ParserContext,
                                                clamping_mode: AllowedNumericType)
                                                -> Result<Number, ParseError<'i>> {
     match try!(input.next()) {
-        Token::Number(ref value) if clamping_mode.is_ok(value.value) => {
+        Token::Number(ref value) if clamping_mode.is_ok(context.parsing_mode, value.value) => {
             Ok(Number {
                 value: value.value.min(f32::MAX).max(f32::MIN),
                 calc_clamping_mode: None,
@@ -364,14 +364,21 @@ impl Time {
                                         input: &mut Parser<'i, 't>,
                                         clamping_mode: AllowedNumericType)
                                         -> Result<Self, ParseError<'i>> {
+        use style_traits::PARSING_MODE_DEFAULT;
+
         match input.next() {
-            Ok(Token::Dimension(ref value, ref unit)) if clamping_mode.is_ok(value.value) => {
+            // Note that we generally pass ParserContext to is_ok() to check
+            // that the ParserMode of the ParserContext allows all numeric
+            // values for SMIL regardless of clamping_mode, but in this Time
+            // value case, the value does not animate for SMIL at all, so we use
+            // PARSING_MODE_DEFAULT directly.
+            Ok(Token::Dimension(ref value, ref unit)) if clamping_mode.is_ok(PARSING_MODE_DEFAULT, value.value) => {
                 Time::parse_dimension(value.value, &unit, /* from_calc = */ false)
                     .map_err(|()| StyleParseError::UnspecifiedError.into())
             }
             Ok(Token::Function(ref name)) if name.eq_ignore_ascii_case("calc") => {
                 match input.parse_nested_block(|i| CalcNode::parse_time(context, i)) {
-                    Ok(time) if clamping_mode.is_ok(time.seconds) => Ok(time),
+                    Ok(time) if clamping_mode.is_ok(PARSING_MODE_DEFAULT, time.seconds) => Ok(time),
                     _ => Err(StyleParseError::UnspecifiedError.into()),
                 }
             }
@@ -457,21 +464,13 @@ impl Number {
     #[allow(missing_docs)]
     pub fn parse_non_negative<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
                                       -> Result<Number, ParseError<'i>> {
-        if context.parsing_mode.allows_all_numeric_values() {
-            parse_number(context, input)
-        } else {
-            parse_number_with_clamping_mode(context, input, AllowedNumericType::NonNegative)
-        }
+        parse_number_with_clamping_mode(context, input, AllowedNumericType::NonNegative)
     }
 
     #[allow(missing_docs)]
     pub fn parse_at_least_one<'i, 't>(context: &ParserContext, input: &mut Parser<'i, 't>)
                                       -> Result<Number, ParseError<'i>> {
-        if context.parsing_mode.allows_all_numeric_values() {
-            parse_number(context, input)
-        } else {
-            parse_number_with_clamping_mode(context, input, AllowedNumericType::AtLeastOne)
-        }
+        parse_number_with_clamping_mode(context, input, AllowedNumericType::AtLeastOne)
     }
 }
 
@@ -522,7 +521,7 @@ impl NumberOrPercentage {
                                         input: &mut Parser<'i, 't>,
                                         type_: AllowedNumericType)
                                         -> Result<Self, ParseError<'i>> {
-        if let Ok(per) = input.try(|i| Percentage::parse_with_clamping_mode(i, type_)) {
+        if let Ok(per) = input.try(|i| Percentage::parse_with_clamping_mode(context, i, type_)) {
             return Ok(NumberOrPercentage::Percentage(per));
         }
 
diff --git a/servo/components/style_traits/Cargo.toml b/servo/components/style_traits/Cargo.toml
index e298fe530534..d668bc8984f6 100644
--- a/servo/components/style_traits/Cargo.toml
+++ b/servo/components/style_traits/Cargo.toml
@@ -16,6 +16,7 @@ gecko = []
 
 [dependencies]
 app_units = "0.4.1"
+bitflags = "0.7"
 cssparser = "0.14.0"
 euclid = "0.13"
 heapsize = {version = "0.4", optional = true}
diff --git a/servo/components/style_traits/lib.rs b/servo/components/style_traits/lib.rs
index 87aa6b330fb9..ed085a12993c 100644
--- a/servo/components/style_traits/lib.rs
+++ b/servo/components/style_traits/lib.rs
@@ -14,6 +14,7 @@
 #![cfg_attr(feature = "servo", feature(plugin))]
 
 extern crate app_units;
+#[macro_use] extern crate bitflags;
 #[macro_use] extern crate cssparser;
 extern crate euclid;
 #[cfg(feature = "servo")] extern crate heapsize;
@@ -140,3 +141,32 @@ impl<'a> From<PropertyDeclarationParseError> for ParseError<'a> {
         cssparser::ParseError::Custom(SelectorParseError::Custom(StyleParseError::PropertyDeclaration(this)))
     }
 }
+
+bitflags! {
+    /// The mode to use when parsing values.
+    pub flags ParsingMode: u8 {
+        /// In CSS, lengths must have units, except for zero values, where the unit can be omitted.
+        /// https://www.w3.org/TR/css3-values/#lengths
+        const PARSING_MODE_DEFAULT = 0x00,
+        /// In SVG, a coordinate or length value without a unit identifier (e.g., "25") is assumed
+        /// to be in user units (px).
+        /// https://www.w3.org/TR/SVG/coords.html#Units
+        const PARSING_MODE_ALLOW_UNITLESS_LENGTH = 0x01,
+        /// In SVG, out-of-range values are not treated as an error in parsing.
+        /// https://www.w3.org/TR/SVG/implnote.html#RangeClamping
+        const PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES = 0x02,
+    }
+}
+
+impl ParsingMode {
+    /// Whether the parsing mode allows unitless lengths for non-zero values to be intpreted as px.
+    pub fn allows_unitless_lengths(&self) -> bool {
+        self.intersects(PARSING_MODE_ALLOW_UNITLESS_LENGTH)
+    }
+
+    /// Whether the parsing mode allows all numeric values.
+    pub fn allows_all_numeric_values(&self) -> bool {
+        self.intersects(PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES)
+    }
+}
+
diff --git a/servo/components/style_traits/values.rs b/servo/components/style_traits/values.rs
index 6c31da166641..3a587ac81f93 100644
--- a/servo/components/style_traits/values.rs
+++ b/servo/components/style_traits/values.rs
@@ -204,6 +204,7 @@ macro_rules! __define_css_keyword_enum__actual {
 
 /// Helper types for the handling of specified values.
 pub mod specified {
+    use ParsingMode;
     use app_units::Au;
     use std::cmp;
 
@@ -228,7 +229,10 @@ pub mod specified {
     impl AllowedLengthType {
         /// Whether value is valid for this allowed length type.
         #[inline]
-        pub fn is_ok(&self, value: f32) -> bool {
+        pub fn is_ok(&self, parsing_mode: ParsingMode, value: f32) -> bool {
+            if parsing_mode.allows_all_numeric_values() {
+                return true;
+            }
             match *self {
                 AllowedLengthType::All => true,
                 AllowedLengthType::NonNegative => value >= 0.,
@@ -261,7 +265,10 @@ pub mod specified {
     impl AllowedNumericType {
         /// Whether the value fits the rules of this numeric type.
         #[inline]
-        pub fn is_ok(&self, val: f32) -> bool {
+        pub fn is_ok(&self, parsing_mode: ParsingMode, val: f32) -> bool {
+            if parsing_mode.allows_all_numeric_values() {
+                return true;
+            }
             match *self {
                 AllowedNumericType::All => true,
                 AllowedNumericType::NonNegative => val >= 0.0,
diff --git a/servo/components/style_traits/viewport.rs b/servo/components/style_traits/viewport.rs
index 9a77a554f295..4bfaef849acd 100644
--- a/servo/components/style_traits/viewport.rs
+++ b/servo/components/style_traits/viewport.rs
@@ -9,7 +9,6 @@ use cssparser::{Parser, ToCss, ParseError as CssParseError, BasicParseError};
 use euclid::size::TypedSize2D;
 use std::ascii::AsciiExt;
 use std::fmt;
-use values::specified::AllowedLengthType;
 
 define_css_keyword_enum!(UserZoom:
                          "zoom" => Zoom,
@@ -141,12 +140,18 @@ impl Zoom {
     ///
     /// https://drafts.csswg.org/css-device-adapt/#descdef-viewport-zoom
     pub fn parse<'i, 't>(input: &mut Parser<'i, 't>) -> Result<Zoom, ParseError<'i>> {
+        use PARSING_MODE_DEFAULT;
         use cssparser::Token;
+        use values::specified::AllowedLengthType::NonNegative;
 
         match try!(input.next()) {
-            Token::Percentage(ref value) if AllowedLengthType::NonNegative.is_ok(value.unit_value) =>
+            // TODO: This parse() method should take ParserContext as an
+            // argument, and pass ParsingMode owned by the ParserContext to
+            // is_ok() instead of using PARSING_MODE_DEFAULT directly.
+            // In order to do so, we might want to move these stuff into style::stylesheets::viewport_rule.
+            Token::Percentage(ref value) if NonNegative.is_ok(PARSING_MODE_DEFAULT, value.unit_value) =>
                 Ok(Zoom::Percentage(value.unit_value)),
-            Token::Number(ref value) if AllowedLengthType::NonNegative.is_ok(value.value) =>
+            Token::Number(ref value) if NonNegative.is_ok(PARSING_MODE_DEFAULT, value.value) =>
                 Ok(Zoom::Number(value.value)),
             Token::Ident(ref value) if value.eq_ignore_ascii_case("auto") =>
                 Ok(Zoom::Auto),
diff --git a/servo/ports/geckolib/glue.rs b/servo/ports/geckolib/glue.rs
index 28abf33b13d2..a3c1ebbe2bc9 100644
--- a/servo/ports/geckolib/glue.rs
+++ b/servo/ports/geckolib/glue.rs
@@ -91,7 +91,7 @@ use style::gecko_properties::{self, style_structs};
 use style::invalidation::element::restyle_hints::{self, RestyleHint};
 use style::media_queries::{MediaList, parse_media_query_list};
 use style::parallel;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::properties::{CascadeFlags, ComputedValues, Importance, SourcePropertyDeclaration};
 use style::properties::{LonghandIdSet, PropertyDeclaration, PropertyDeclarationBlock, PropertyId, StyleBuilder};
 use style::properties::SKIP_ROOT_AND_ITEM_BASED_DISPLAY_FIXUP;
@@ -118,7 +118,7 @@ use style::traversal::{FOR_DEFAULT_STYLES, TraversalDriver, TraversalFlags, UNST
 use style::traversal::{resolve_style, resolve_default_style};
 use style::values::{CustomIdent, KeyframesName};
 use style::values::computed::Context;
-use style_traits::ToCss;
+use style_traits::{PARSING_MODE_DEFAULT, ToCss};
 use super::stylesheet_loader::StylesheetLoader;
 
 /*
@@ -1594,7 +1594,7 @@ fn parse_property_into(declarations: &mut SourcePropertyDeclaration,
                        data: *mut URLExtraData,
                        parsing_mode: structs::ParsingMode,
                        quirks_mode: QuirksMode) -> Result<(), ()> {
-    use style::parser::ParsingMode;
+    use style_traits::ParsingMode;
     let value = unsafe { value.as_ref().unwrap().as_str_unchecked() };
     let url_data = unsafe { RefPtr::from_ptr_ref(&data) };
     let parsing_mode = ParsingMode::from_bits_truncate(parsing_mode);
diff --git a/servo/tests/unit/style/parsing/length.rs b/servo/tests/unit/style/parsing/length.rs
index b779208d42e1..8144999f307e 100644
--- a/servo/tests/unit/style/parsing/length.rs
+++ b/servo/tests/unit/style/parsing/length.rs
@@ -6,12 +6,12 @@ use cssparser::{Parser, ParserInput};
 use media_queries::CSSErrorReporterTest;
 use parsing::parse;
 use style::context::QuirksMode;
-use style::parser::{PARSING_MODE_ALLOW_UNITLESS_LENGTH, Parse, ParserContext};
+use style::parser::{Parse, ParserContext};
 use style::stylesheets::{CssRuleType, Origin};
 use style::values::Either;
 use style::values::specified::{LengthOrPercentageOrNumber, Number};
 use style::values::specified::length::{AbsoluteLength, Length, NoCalcLength};
-use style_traits::ToCss;
+use style_traits::{PARSING_MODE_ALLOW_UNITLESS_LENGTH, ToCss};
 
 #[test]
 fn test_calc() {
diff --git a/servo/tests/unit/style/parsing/mod.rs b/servo/tests/unit/style/parsing/mod.rs
index e01b681e3c74..c0c357b390ab 100644
--- a/servo/tests/unit/style/parsing/mod.rs
+++ b/servo/tests/unit/style/parsing/mod.rs
@@ -10,11 +10,11 @@ use media_queries::CSSErrorReporterTest;
 use style::context::QuirksMode;
 use style::font_metrics::ServoMetricsProvider;
 use style::media_queries::{Device, MediaType};
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::properties::{ComputedValues, StyleBuilder};
 use style::stylesheets::{CssRuleType, Origin};
 use style::values::computed::{Context, ToComputedValue};
-use style_traits::{ToCss, ParseError};
+use style_traits::{PARSING_MODE_DEFAULT, ToCss, ParseError};
 
 fn parse<T, F>(f: F, s: &'static str) -> Result<T, ParseError<'static>>
 where F: for<'t> Fn(&ParserContext, &mut Parser<'static, 't>) -> Result<T, ParseError<'static>> {
diff --git a/servo/tests/unit/style/parsing/value.rs b/servo/tests/unit/style/parsing/value.rs
index 983f7fced47c..7b4f0917c58c 100644
--- a/servo/tests/unit/style/parsing/value.rs
+++ b/servo/tests/unit/style/parsing/value.rs
@@ -6,10 +6,10 @@ use app_units::Au;
 use cssparser::{Parser, ParserInput};
 use media_queries::CSSErrorReporterTest;
 use style::context::QuirksMode;
-use style::parser::{PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES, ParserContext};
+use style::parser::ParserContext;
 use style::stylesheets::{CssRuleType, Origin};
 use style::values::specified::{AbsoluteLength, NoCalcLength, Number, ViewportPercentageLength};
-use style_traits::HasViewportPercentage;
+use style_traits::{PARSING_MODE_ALLOW_ALL_NUMERIC_VALUES, HasViewportPercentage};
 
 #[test]
 fn length_has_viewport_percentage() {
diff --git a/servo/tests/unit/style/properties/mod.rs b/servo/tests/unit/style/properties/mod.rs
index 766b7e3e3b52..96d66655f56c 100644
--- a/servo/tests/unit/style/properties/mod.rs
+++ b/servo/tests/unit/style/properties/mod.rs
@@ -5,9 +5,9 @@
 use cssparser::{Parser, ParserInput};
 use media_queries::CSSErrorReporterTest;
 use style::context::QuirksMode;
-use style::parser::{PARSING_MODE_DEFAULT, ParserContext};
+use style::parser::ParserContext;
 use style::stylesheets::{CssRuleType, Origin};
-use style_traits::ParseError;
+use style_traits::{PARSING_MODE_DEFAULT, ParseError};
 
 fn parse<T, F>(f: F, s: &'static str) -> Result<T, ParseError<'static>>
 where F: for<'t> Fn(&ParserContext, &mut Parser<'static, 't>) -> Result<T, ParseError<'static>> {
diff --git a/servo/tests/unit/style/viewport.rs b/servo/tests/unit/style/viewport.rs
index 87c4c54f9b08..f3903f35fc5b 100644
--- a/servo/tests/unit/style/viewport.rs
+++ b/servo/tests/unit/style/viewport.rs
@@ -9,7 +9,7 @@ use servo_config::prefs::{PREFS, PrefValue};
 use servo_url::ServoUrl;
 use style::context::QuirksMode;
 use style::media_queries::{Device, MediaList, MediaType};
-use style::parser::{PARSING_MODE_DEFAULT, Parse, ParserContext};
+use style::parser::{Parse, ParserContext};
 use style::shared_lock::SharedRwLock;
 use style::stylearc::Arc;
 use style::stylesheets::{CssRuleType, Stylesheet, Origin};
@@ -17,7 +17,7 @@ use style::stylesheets::viewport_rule::*;
 use style::values::specified::LengthOrPercentageOrAuto::{self, Auto};
 use style::values::specified::NoCalcLength::{self, ViewportPercentage};
 use style::values::specified::ViewportPercentageLength::Vw;
-use style_traits::PinchZoomFactor;
+use style_traits::{PARSING_MODE_DEFAULT, PinchZoomFactor};
 use style_traits::viewport::*;
 
 macro_rules! stylesheet {