diff --git a/components/selectors/builder.rs b/components/selectors/builder.rs
new file mode 100644
index 00000000000..9fd751b9bb8
--- /dev/null
+++ b/components/selectors/builder.rs
@@ -0,0 +1,141 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use parser::{Component, SelectorImpl, SelectorIter};
+use std::cmp;
+use std::ops::Add;
+
+#[derive(Copy, Clone, Debug, Eq, PartialEq)]
+pub struct SpecificityAndFlags(pub u32);
+
+pub const HAS_PSEUDO_BIT: u32 = 1 << 30;
+
+impl SpecificityAndFlags {
+    pub fn specificity(&self) -> u32 {
+        self.0 & !HAS_PSEUDO_BIT
+    }
+
+    pub fn has_pseudo_element(&self) -> bool {
+        (self.0 & HAS_PSEUDO_BIT) != 0
+    }
+}
+
+const MAX_10BIT: u32 = (1u32 << 10) - 1;
+
+#[derive(Clone, Copy, Eq, Ord, PartialEq, PartialOrd)]
+struct Specificity {
+    id_selectors: u32,
+    class_like_selectors: u32,
+    element_selectors: u32,
+}
+
+impl Add for Specificity {
+    type Output = Specificity;
+
+    fn add(self, rhs: Specificity) -> Specificity {
+        Specificity {
+            id_selectors: self.id_selectors + rhs.id_selectors,
+            class_like_selectors:
+                self.class_like_selectors + rhs.class_like_selectors,
+            element_selectors:
+                self.element_selectors + rhs.element_selectors,
+        }
+    }
+}
+
+impl Default for Specificity {
+    fn default() -> Specificity {
+        Specificity {
+            id_selectors: 0,
+            class_like_selectors: 0,
+            element_selectors: 0,
+        }
+    }
+}
+
+impl From<u32> for Specificity {
+    fn from(value: u32) -> Specificity {
+        assert!(value <= MAX_10BIT << 20 | MAX_10BIT << 10 | MAX_10BIT);
+        Specificity {
+            id_selectors: value >> 20,
+            class_like_selectors: (value >> 10) & MAX_10BIT,
+            element_selectors: value & MAX_10BIT,
+        }
+    }
+}
+
+impl From<Specificity> for u32 {
+    fn from(specificity: Specificity) -> u32 {
+        cmp::min(specificity.id_selectors, MAX_10BIT) << 20
+        | cmp::min(specificity.class_like_selectors, MAX_10BIT) << 10
+        | cmp::min(specificity.element_selectors, MAX_10BIT)
+    }
+}
+
+pub fn specificity<Impl>(iter: SelectorIter<Impl>) -> u32
+    where Impl: SelectorImpl
+{
+    complex_selector_specificity(iter).into()
+}
+
+fn complex_selector_specificity<Impl>(mut iter: SelectorIter<Impl>)
+                                      -> Specificity
+    where Impl: SelectorImpl
+{
+    fn simple_selector_specificity<Impl>(simple_selector: &Component<Impl>,
+                                         specificity: &mut Specificity)
+        where Impl: SelectorImpl
+    {
+        match *simple_selector {
+            Component::Combinator(..) => unreachable!(),
+            Component::PseudoElement(..) |
+            Component::LocalName(..) => {
+                specificity.element_selectors += 1
+            }
+            Component::ID(..) => {
+                specificity.id_selectors += 1
+            }
+            Component::Class(..) |
+            Component::AttributeInNoNamespace { .. } |
+            Component::AttributeInNoNamespaceExists { .. } |
+            Component::AttributeOther(..) |
+
+            Component::FirstChild | Component::LastChild |
+            Component::OnlyChild | Component::Root |
+            Component::Empty |
+            Component::NthChild(..) |
+            Component::NthLastChild(..) |
+            Component::NthOfType(..) |
+            Component::NthLastOfType(..) |
+            Component::FirstOfType | Component::LastOfType |
+            Component::OnlyOfType |
+            Component::NonTSPseudoClass(..) => {
+                specificity.class_like_selectors += 1
+            }
+            Component::ExplicitUniversalType |
+            Component::ExplicitAnyNamespace |
+            Component::ExplicitNoNamespace |
+            Component::DefaultNamespace(..) |
+            Component::Namespace(..) => {
+                // Does not affect specificity
+            }
+            Component::Negation(ref negated) => {
+                for ss in negated.iter() {
+                    simple_selector_specificity(&ss, specificity);
+                }
+            }
+        }
+    }
+
+    let mut specificity = Default::default();
+    loop {
+        for simple_selector in &mut iter {
+            simple_selector_specificity(&simple_selector, &mut specificity);
+        }
+        if iter.next_sequence().is_none() {
+            break;
+        }
+    }
+    specificity
+}
diff --git a/components/selectors/lib.rs b/components/selectors/lib.rs
index bde7acef189..568e1aaba70 100644
--- a/components/selectors/lib.rs
+++ b/components/selectors/lib.rs
@@ -15,6 +15,7 @@ extern crate smallvec;
 
 pub mod attr;
 pub mod bloom;
+mod builder;
 pub mod context;
 pub mod matching;
 pub mod parser;
diff --git a/components/selectors/parser.rs b/components/selectors/parser.rs
index fe1214aafa0..f61a42c51d8 100644
--- a/components/selectors/parser.rs
+++ b/components/selectors/parser.rs
@@ -5,6 +5,8 @@
 use attr::{AttrSelectorWithNamespace, ParsedAttrSelectorOperation, AttrSelectorOperator};
 use attr::{ParsedCaseSensitivity, SELECTOR_WHITESPACE, NamespaceConstraint};
 use bloom::BLOOM_HASH_MASK;
+use builder::{HAS_PSEUDO_BIT, SpecificityAndFlags};
+use builder::specificity;
 use cssparser::{ParseError, BasicParseError, CompactCowStr};
 use cssparser::{Token, Parser as CssParser, parse_nth, ToCss, serialize_identifier, CssStringWriter};
 use precomputed_hash::PrecomputedHash;
@@ -13,10 +15,8 @@ use sink::Push;
 use smallvec::SmallVec;
 use std::ascii::AsciiExt;
 use std::borrow::{Borrow, Cow};
-use std::cmp;
 use std::fmt::{self, Display, Debug, Write};
 use std::iter::Rev;
-use std::ops::Add;
 use std::slice;
 use visitor::SelectorVisitor;
 
@@ -266,8 +266,6 @@ impl AncestorHashes {
     }
 }
 
-const HAS_PSEUDO_BIT: u32 = 1 << 30;
-
 pub trait SelectorMethods {
     type Impl: SelectorImpl;
 
@@ -370,19 +368,6 @@ pub fn namespace_empty_string<Impl: SelectorImpl>() -> Impl::NamespaceUrl {
     Impl::NamespaceUrl::default()
 }
 
-#[derive(Copy, Clone, Debug, Eq, PartialEq)]
-struct SpecificityAndFlags(u32);
-
-impl SpecificityAndFlags {
-    fn specificity(&self) -> u32 {
-        self.0 & !HAS_PSEUDO_BIT
-    }
-
-    fn has_pseudo_element(&self) -> bool {
-        (self.0 & HAS_PSEUDO_BIT) != 0
-    }
-}
-
 /// A Selector stores a sequence of simple selectors and combinators. The
 /// iterator classes allow callers to iterate at either the raw sequence level or
 /// at the level of sequences of simple selectors separated by combinators. Most
@@ -920,125 +905,6 @@ fn display_to_css_identifier<T: Display, W: fmt::Write>(x: &T, dest: &mut W) ->
     serialize_identifier(&string, dest)
 }
 
-const MAX_10BIT: u32 = (1u32 << 10) - 1;
-
-#[derive(Clone, Copy, Eq, Ord, PartialEq, PartialOrd)]
-struct Specificity {
-    id_selectors: u32,
-    class_like_selectors: u32,
-    element_selectors: u32,
-}
-
-impl Add for Specificity {
-    type Output = Specificity;
-
-    fn add(self, rhs: Specificity) -> Specificity {
-        Specificity {
-            id_selectors: self.id_selectors + rhs.id_selectors,
-            class_like_selectors:
-                self.class_like_selectors + rhs.class_like_selectors,
-            element_selectors:
-                self.element_selectors + rhs.element_selectors,
-        }
-    }
-}
-
-impl Default for Specificity {
-    fn default() -> Specificity {
-        Specificity {
-            id_selectors: 0,
-            class_like_selectors: 0,
-            element_selectors: 0,
-        }
-    }
-}
-
-impl From<u32> for Specificity {
-    fn from(value: u32) -> Specificity {
-        assert!(value <= MAX_10BIT << 20 | MAX_10BIT << 10 | MAX_10BIT);
-        Specificity {
-            id_selectors: value >> 20,
-            class_like_selectors: (value >> 10) & MAX_10BIT,
-            element_selectors: value & MAX_10BIT,
-        }
-    }
-}
-
-impl From<Specificity> for u32 {
-    fn from(specificity: Specificity) -> u32 {
-        cmp::min(specificity.id_selectors, MAX_10BIT) << 20
-        | cmp::min(specificity.class_like_selectors, MAX_10BIT) << 10
-        | cmp::min(specificity.element_selectors, MAX_10BIT)
-    }
-}
-
-fn specificity<Impl>(iter: SelectorIter<Impl>) -> u32
-    where Impl: SelectorImpl
-{
-    complex_selector_specificity(iter).into()
-}
-
-fn complex_selector_specificity<Impl>(mut iter: SelectorIter<Impl>)
-                                      -> Specificity
-    where Impl: SelectorImpl
-{
-    fn simple_selector_specificity<Impl>(simple_selector: &Component<Impl>,
-                                         specificity: &mut Specificity)
-        where Impl: SelectorImpl
-    {
-        match *simple_selector {
-            Component::Combinator(..) => unreachable!(),
-            Component::PseudoElement(..) |
-            Component::LocalName(..) => {
-                specificity.element_selectors += 1
-            }
-            Component::ID(..) => {
-                specificity.id_selectors += 1
-            }
-            Component::Class(..) |
-            Component::AttributeInNoNamespace { .. } |
-            Component::AttributeInNoNamespaceExists { .. } |
-            Component::AttributeOther(..) |
-
-            Component::FirstChild | Component::LastChild |
-            Component::OnlyChild | Component::Root |
-            Component::Empty |
-            Component::NthChild(..) |
-            Component::NthLastChild(..) |
-            Component::NthOfType(..) |
-            Component::NthLastOfType(..) |
-            Component::FirstOfType | Component::LastOfType |
-            Component::OnlyOfType |
-            Component::NonTSPseudoClass(..) => {
-                specificity.class_like_selectors += 1
-            }
-            Component::ExplicitUniversalType |
-            Component::ExplicitAnyNamespace |
-            Component::ExplicitNoNamespace |
-            Component::DefaultNamespace(..) |
-            Component::Namespace(..) => {
-                // Does not affect specificity
-            }
-            Component::Negation(ref negated) => {
-                for ss in negated.iter() {
-                    simple_selector_specificity(&ss, specificity);
-                }
-            }
-        }
-    }
-
-    let mut specificity = Default::default();
-    loop {
-        for simple_selector in &mut iter {
-            simple_selector_specificity(&simple_selector, &mut specificity);
-        }
-        if iter.next_sequence().is_none() {
-            break;
-        }
-    }
-    specificity
-}
-
 /// We make this large because the result of parsing a selector is fed into a new
 /// Arc-ed allocation, so any spilled vec would be a wasted allocation. Also,
 /// Components are large enough that we don't have much cache locality benefit