diff --git a/lib/nokogiri/css/parser.rb b/lib/nokogiri/css/parser.rb
index 5cdc80d44b..5d67e4f16a 100644
--- a/lib/nokogiri/css/parser.rb
+++ b/lib/nokogiri/css/parser.rb
@@ -1,4 +1,3 @@
-# frozen_string_literal: true
 #
 # DO NOT MODIFY!!!!
 # This file is automatically generated by Racc 1.6.0
@@ -341,7 +340,7 @@ def unescape_css_string(str)
 # reduce 0 omitted
 
 def _reduce_1(val, _values, result)
-        result = [val.first, val.last].flatten
+      result = [val[0], val[2]].flatten
 
     result
 end
@@ -352,7 +351,7 @@ def _reduce_2(val, _values, result)
 end
 
 def _reduce_3(val, _values, result)
- result = [val.last].flatten
+ result = [val[1]].flatten
     result
 end
 
@@ -382,11 +381,11 @@ def _reduce_8(val, _values, result)
 end
 
 def _reduce_9(val, _values, result)
-        result =  if val[1].nil?
-                    val.first
-                  else
-                    Node.new(:CONDITIONAL_SELECTOR, [val.first, val[1]])
-                  end
+      result =  if val[1].nil?
+                  val[0]
+                else
+                  Node.new(:CONDITIONAL_SELECTOR, [val[0], val[1]])
+                end
 
     result
 end
@@ -394,39 +393,39 @@ def _reduce_9(val, _values, result)
 # reduce 10 omitted
 
 def _reduce_11(val, _values, result)
-        result = Node.new(:CONDITIONAL_SELECTOR, val)
+      result = Node.new(:CONDITIONAL_SELECTOR, val)
 
     result
 end
 
 def _reduce_12(val, _values, result)
-        result = Node.new(:CONDITIONAL_SELECTOR, val)
+      result = Node.new(:CONDITIONAL_SELECTOR, val)
 
     result
 end
 
 def _reduce_13(val, _values, result)
-        result = Node.new(:CONDITIONAL_SELECTOR,
-          [Node.new(:ELEMENT_NAME, ['*']), val.first]
-        )
+      result = Node.new(:CONDITIONAL_SELECTOR,
+        [Node.new(:ELEMENT_NAME, ['*']), val[0]]
+      )
 
     result
 end
 
 def _reduce_14(val, _values, result)
-        result = Node.new(val.first, [nil, val.last])
+      result = Node.new(val[0], [nil, val[1]])
 
     result
 end
 
 def _reduce_15(val, _values, result)
-        result = Node.new(val[1], [val.first, val.last])
+      result = Node.new(val[1], [val[0], val[2]])
 
     result
 end
 
 def _reduce_16(val, _values, result)
-        result = Node.new(:DESCENDANT_SELECTOR, [val.first, val.last])
+      result = Node.new(:DESCENDANT_SELECTOR, [val[0], val[2]])
 
     result
 end
@@ -446,16 +445,16 @@ def _reduce_20(val, _values, result)
 end
 
 def _reduce_21(val, _values, result)
-        result = Node.new(:ELEMENT_NAME,
-          [[val.first, val.last].compact.join(':')]
-        )
+      result = Node.new(:ELEMENT_NAME,
+        [[val[0], val[2]].compact.join(':')]
+      )
 
     result
 end
 
 def _reduce_22(val, _values, result)
-        name = @namespaces.key?('xmlns') ? "xmlns:#{val.first}" : val.first
-        result = Node.new(:ELEMENT_NAME, [name])
+      name = @namespaces.key?('xmlns') ? "xmlns:#{val[0]}" : val[0]
+      result = Node.new(:ELEMENT_NAME, [name])
 
     result
 end
@@ -468,88 +467,88 @@ def _reduce_23(val, _values, result)
 # reduce 24 omitted
 
 def _reduce_25(val, _values, result)
-        result = Node.new(:ATTRIBUTE_CONDITION,
-          [val[1]] + (val[2] || [])
-        )
+      result = Node.new(:ATTRIBUTE_CONDITION,
+        [val[1]] + (val[2] || [])
+      )
 
     result
 end
 
 def _reduce_26(val, _values, result)
-        result = Node.new(:ATTRIBUTE_CONDITION,
-          [val[1]] + (val[2] || [])
-        )
+      result = Node.new(:ATTRIBUTE_CONDITION,
+        [val[1]] + (val[2] || [])
+      )
 
     result
 end
 
 def _reduce_27(val, _values, result)
-        # non-standard, from hpricot
-        result = Node.new(:PSEUDO_CLASS,
-          [Node.new(:FUNCTION, ['nth-child(', val[1]])]
-        )
+      # non-standard, from hpricot
+      result = Node.new(:PSEUDO_CLASS,
+        [Node.new(:FUNCTION, ['nth-child(', val[1]])]
+      )
 
     result
 end
 
 def _reduce_28(val, _values, result)
-        result = Node.new(:ATTRIB_NAME,
-          [[val.first, val.last].compact.join(':')]
-        )
+      result = Node.new(:ATTRIB_NAME,
+        [[val[0], val[2]].compact.join(':')]
+      )
 
     result
 end
 
 def _reduce_29(val, _values, result)
-        # Default namespace is not applied to attributes.
-        # So we don't add prefix "xmlns:" as in namespaced_ident.
-        result = Node.new(:ATTRIB_NAME, [val.first])
+      # Default namespace is not applied to attributes.
+      # So we don't add prefix "xmlns:" as in namespaced_ident.
+      result = Node.new(:ATTRIB_NAME, [val[0]])
 
     result
 end
 
 def _reduce_30(val, _values, result)
-        result = Node.new(:FUNCTION, [val.first.strip])
+      result = Node.new(:FUNCTION, [val[0].strip])
 
     result
 end
 
 def _reduce_31(val, _values, result)
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
 
     result
 end
 
 def _reduce_32(val, _values, result)
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
 
     result
 end
 
 def _reduce_33(val, _values, result)
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
 
     result
 end
 
 def _reduce_34(val, _values, result)
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
 
     result
 end
 
 def _reduce_35(val, _values, result)
- result = [val.first, val.last]
+ result = [val[0], val[2]]
     result
 end
 
 def _reduce_36(val, _values, result)
- result = [val.first, val.last]
+ result = [val[0], val[2]]
     result
 end
 
 def _reduce_37(val, _values, result)
- result = [val.first, val.last]
+ result = [val[0], val[2]]
     result
 end
 
@@ -558,72 +557,68 @@ def _reduce_37(val, _values, result)
 # reduce 39 omitted
 
 def _reduce_40(val, _values, result)
-        case val[0]
-        when 'even'
-          result = Node.new(:NTH, ['2','n','+','0'])
-        when 'odd'
-          result = Node.new(:NTH, ['2','n','+','1'])
-        when 'n'
-          result = Node.new(:NTH, ['1','n','+','0'])
-        else
-          # non-standard to support custom functions:
-          # assert_xpath("//a[foo(., @href)]", @parser.parse('a:foo(@href)'))
-          # assert_xpath("//a[foo(., @a, b)]", @parser.parse('a:foo(@a, b)'))
-          # assert_xpath("//a[foo(., a, 10)]", @parser.parse('a:foo(a, 10)'))
-          result = val
-        end
+      case val[0]
+      when 'even'
+        result = Node.new(:NTH, ['2','n','+','0'])
+      when 'odd'
+        result = Node.new(:NTH, ['2','n','+','1'])
+      when 'n'
+        result = Node.new(:NTH, ['1','n','+','0'])
+      else
+        result = val
+      end
 
     result
 end
 
 def _reduce_41(val, _values, result)
-        if val[1] == 'n'
-          result = Node.new(:NTH, val)
-        else
-          raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
-        end
+      if val[1] == 'n'
+        result = Node.new(:NTH, val)
+      else
+        raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
+      end
 
     result
 end
 
 def _reduce_42(val, _values, result)
                # n+3, -n+3
-        if val[0] == 'n'
-          val.unshift("1")
-          result = Node.new(:NTH, val)
-        elsif val[0] == '-n'
-          val[0] = 'n'
-          val.unshift("-1")
-          result = Node.new(:NTH, val)
-        else
-          raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
-        end
+      if val[0] == 'n'
+        val.unshift("1")
+        result = Node.new(:NTH, val)
+      elsif val[0] == '-n'
+        val[0] = 'n'
+        val.unshift("-1")
+        result = Node.new(:NTH, val)
+      else
+        raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
+      end
 
     result
 end
 
 def _reduce_43(val, _values, result)
                     # 5n, -5n, 10n-1
-        n = val[1]
-        if n[0, 2] == 'n-'
-          val[1] = 'n'
-          val << "-"
-          # b is contained in n as n is the string "n-b"
-          val << n[2, n.size]
-          result = Node.new(:NTH, val)
-        elsif n == 'n'
-          val << "+"
-          val << "0"
-          result = Node.new(:NTH, val)
-        else
-          raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
-        end
+      n = val[1]
+      if n[0, 2] == 'n-'
+        val[1] = 'n'
+        val << "-"
+        # b is contained in n as n is the string "n-b"
+        val << n[2, n.size]
+        result = Node.new(:NTH, val)
+      elsif n == 'n'
+        val << "+"
+        val << "0"
+        result = Node.new(:NTH, val)
+      else
+        raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
+      end
 
     result
 end
 
 def _reduce_44(val, _values, result)
-        result = Node.new(:PSEUDO_CLASS, [val[1]])
+      result = Node.new(:PSEUDO_CLASS, [val[1]])
 
     result
 end
@@ -638,31 +633,31 @@ def _reduce_45(val, _values, result)
 # reduce 47 omitted
 
 def _reduce_48(val, _values, result)
-        result = Node.new(:COMBINATOR, val)
+      result = Node.new(:COMBINATOR, val)
 
     result
 end
 
 def _reduce_49(val, _values, result)
-        result = Node.new(:COMBINATOR, val)
+      result = Node.new(:COMBINATOR, val)
 
     result
 end
 
 def _reduce_50(val, _values, result)
-        result = Node.new(:COMBINATOR, val)
+      result = Node.new(:COMBINATOR, val)
 
     result
 end
 
 def _reduce_51(val, _values, result)
-        result = Node.new(:COMBINATOR, val)
+      result = Node.new(:COMBINATOR, val)
 
     result
 end
 
 def _reduce_52(val, _values, result)
-        result = Node.new(:COMBINATOR, val)
+      result = Node.new(:COMBINATOR, val)
 
     result
 end
@@ -678,22 +673,22 @@ def _reduce_52(val, _values, result)
 # reduce 57 omitted
 
 def _reduce_58(val, _values, result)
- result = Node.new(:ID, [unescape_css_identifier(val.first)])
+ result = Node.new(:ID, [unescape_css_identifier(val[0])])
     result
 end
 
 def _reduce_59(val, _values, result)
- result = [val.first, unescape_css_identifier(val[1])]
+ result = [val[0], unescape_css_identifier(val[1])]
     result
 end
 
 def _reduce_60(val, _values, result)
- result = [val.first, unescape_css_string(val[1])]
+ result = [val[0], unescape_css_string(val[1])]
     result
 end
 
 def _reduce_61(val, _values, result)
- result = [val.first, val[1]]
+ result = [val[0], val[1]]
     result
 end
 
@@ -735,7 +730,7 @@ def _reduce_69(val, _values, result)
 end
 
 def _reduce_70(val, _values, result)
-        result = Node.new(:NOT, [val[1]])
+      result = Node.new(:NOT, [val[1]])
 
     result
 end
diff --git a/lib/nokogiri/css/parser.y b/lib/nokogiri/css/parser.y
index d5c4af1f6c..6f1733ffe9 100644
--- a/lib/nokogiri/css/parser.y
+++ b/lib/nokogiri/css/parser.y
@@ -5,250 +5,268 @@ token COMMA NUMBER PREFIXMATCH SUFFIXMATCH SUBSTRINGMATCH TILDE NOT_EQUAL
 token SLASH DOUBLESLASH NOT EQUAL RPAREN LSQUARE RSQUARE HAS
 
 rule
-  selector
-    : selector COMMA simple_selector_1toN {
-        result = [val.first, val.last].flatten
-      }
-    | prefixless_combinator_selector { result = val.flatten }
-    | optional_S simple_selector_1toN { result = [val.last].flatten }
-    ;
-  combinator
-    : PLUS { result = :DIRECT_ADJACENT_SELECTOR }
-    | GREATER { result = :CHILD_SELECTOR }
-    | TILDE { result = :FOLLOWING_SELECTOR }
-    | DOUBLESLASH { result = :DESCENDANT_SELECTOR }
-    | SLASH { result = :CHILD_SELECTOR }
-    ;
-  simple_selector
-    : element_name hcap_0toN {
-        result =  if val[1].nil?
-                    val.first
-                  else
-                    Node.new(:CONDITIONAL_SELECTOR, [val.first, val[1]])
-                  end
-      }
-    | function
-    | function pseudo {
-        result = Node.new(:CONDITIONAL_SELECTOR, val)
-      }
-    | function attrib {
-        result = Node.new(:CONDITIONAL_SELECTOR, val)
-      }
-    | hcap_1toN {
-        result = Node.new(:CONDITIONAL_SELECTOR,
-          [Node.new(:ELEMENT_NAME, ['*']), val.first]
-        )
-      }
-    ;
-  prefixless_combinator_selector
-    : combinator simple_selector_1toN {
-        result = Node.new(val.first, [nil, val.last])
-      }
-    ;
-  simple_selector_1toN
-    : simple_selector combinator simple_selector_1toN {
-        result = Node.new(val[1], [val.first, val.last])
-      }
-    | simple_selector S simple_selector_1toN {
-        result = Node.new(:DESCENDANT_SELECTOR, [val.first, val.last])
-      }
-    | simple_selector
-    ;
-  class
-    : '.' IDENT { result = Node.new(:CLASS_CONDITION, [unescape_css_identifier(val[1])]) }
-    ;
-  element_name
-    : namespaced_ident
-    | '*' { result = Node.new(:ELEMENT_NAME, val) }
-    ;
-  namespaced_ident
-    : namespace '|' IDENT {
-        result = Node.new(:ELEMENT_NAME,
-          [[val.first, val.last].compact.join(':')]
-        )
-      }
-    | IDENT {
-        name = @namespaces.key?('xmlns') ? "xmlns:#{val.first}" : val.first
-        result = Node.new(:ELEMENT_NAME, [name])
-      }
-    ;
-  namespace
-    : IDENT { result = val[0] }
-    |
-    ;
-  attrib
-    : LSQUARE attrib_name attrib_val_0or1 RSQUARE {
-        result = Node.new(:ATTRIBUTE_CONDITION,
-          [val[1]] + (val[2] || [])
-        )
-      }
-    | LSQUARE function attrib_val_0or1 RSQUARE {
-        result = Node.new(:ATTRIBUTE_CONDITION,
-          [val[1]] + (val[2] || [])
-        )
-      }
-    | LSQUARE NUMBER RSQUARE {
-        # non-standard, from hpricot
-        result = Node.new(:PSEUDO_CLASS,
-          [Node.new(:FUNCTION, ['nth-child(', val[1]])]
-        )
-      }
-    ;
-  attrib_name
-    : namespace '|' IDENT {
-        result = Node.new(:ATTRIB_NAME,
-          [[val.first, val.last].compact.join(':')]
-        )
-      }
-    | IDENT {
-        # Default namespace is not applied to attributes.
-        # So we don't add prefix "xmlns:" as in namespaced_ident.
-        result = Node.new(:ATTRIB_NAME, [val.first])
-      }
-    ;
-  function
-    : FUNCTION RPAREN {
-        result = Node.new(:FUNCTION, [val.first.strip])
-      }
-    | FUNCTION expr RPAREN {
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
-      }
-    | FUNCTION nth RPAREN {
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
-      }
-    | NOT expr RPAREN {
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
-      }
-    | HAS selector RPAREN {
-        result = Node.new(:FUNCTION, [val.first.strip, val[1]].flatten)
-      }
-    ;
-  expr
-    : NUMBER COMMA expr { result = [val.first, val.last] }
-    | STRING COMMA expr { result = [val.first, val.last] }
-    | IDENT COMMA expr { result = [val.first, val.last] }
-    | NUMBER
-    | STRING
-    | IDENT                             # even, odd
-      {
-        case val[0]
-        when 'even'
-          result = Node.new(:NTH, ['2','n','+','0'])
-        when 'odd'
-          result = Node.new(:NTH, ['2','n','+','1'])
-        when 'n'
-          result = Node.new(:NTH, ['1','n','+','0'])
-        else
-          # non-standard to support custom functions:
-          # assert_xpath("//a[foo(., @href)]", @parser.parse('a:foo(@href)'))
-          # assert_xpath("//a[foo(., @a, b)]", @parser.parse('a:foo(@a, b)'))
-          # assert_xpath("//a[foo(., a, 10)]", @parser.parse('a:foo(a, 10)'))
-          result = val
-        end
-      }
-    ;
-  nth
-    : NUMBER IDENT PLUS NUMBER          # 5n+3 -5n+3
-      {
-        if val[1] == 'n'
-          result = Node.new(:NTH, val)
-        else
-          raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
-        end
-      }
-    | IDENT PLUS NUMBER {               # n+3, -n+3
-        if val[0] == 'n'
-          val.unshift("1")
-          result = Node.new(:NTH, val)
-        elsif val[0] == '-n'
-          val[0] = 'n'
-          val.unshift("-1")
-          result = Node.new(:NTH, val)
-        else
-          raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
-        end
-      }
-    | NUMBER IDENT {                    # 5n, -5n, 10n-1
-        n = val[1]
-        if n[0, 2] == 'n-'
-          val[1] = 'n'
-          val << "-"
-          # b is contained in n as n is the string "n-b"
-          val << n[2, n.size]
-          result = Node.new(:NTH, val)
-        elsif n == 'n'
-          val << "+"
-          val << "0"
-          result = Node.new(:NTH, val)
-        else
-          raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
-        end
-      }
-    ;
-  pseudo
-    : ':' function {
-        result = Node.new(:PSEUDO_CLASS, [val[1]])
-      }
-    | ':' IDENT { result = Node.new(:PSEUDO_CLASS, [val[1]]) }
-    ;
-  hcap_0toN
-    : hcap_1toN
-    |
-    ;
-  hcap_1toN
-    : attribute_id hcap_1toN {
-        result = Node.new(:COMBINATOR, val)
-      }
-    | class hcap_1toN {
-        result = Node.new(:COMBINATOR, val)
-      }
-    | attrib hcap_1toN {
-        result = Node.new(:COMBINATOR, val)
-      }
-    | pseudo hcap_1toN {
-        result = Node.new(:COMBINATOR, val)
-      }
-    | negation hcap_1toN {
-        result = Node.new(:COMBINATOR, val)
-      }
-    | attribute_id
-    | class
-    | attrib
-    | pseudo
-    | negation
-    ;
-  attribute_id
-    : HASH { result = Node.new(:ID, [unescape_css_identifier(val.first)]) }
-    ;
-  attrib_val_0or1
-    : eql_incl_dash IDENT { result = [val.first, unescape_css_identifier(val[1])] }
-    | eql_incl_dash STRING { result = [val.first, unescape_css_string(val[1])] }
-    | eql_incl_dash NUMBER { result = [val.first, val[1]] }
-    |
-    ;
-  eql_incl_dash
-    : EQUAL           { result = :equal }
-    | PREFIXMATCH     { result = :prefix_match }
-    | SUFFIXMATCH     { result = :suffix_match }
-    | SUBSTRINGMATCH  { result = :substring_match }
-    | NOT_EQUAL       { result = :not_equal }
-    | INCLUDES        { result = :includes }
-    | DASHMATCH       { result = :dash_match }
-    ;
-  negation
-    : NOT negation_arg RPAREN {
-        result = Node.new(:NOT, [val[1]])
-      }
-    ;
-  negation_arg
-    : element_name
-    | element_name hcap_1toN
-    | hcap_1toN
-    ;
-  optional_S
-    : S
-    |
-    ;
+  selector:
+    selector COMMA simple_selector_1toN {
+      result = [val[0], val[2]].flatten
+    }
+  | prefixless_combinator_selector { result = val.flatten }
+  | optional_S simple_selector_1toN { result = [val[1]].flatten }
+  ;
+
+  combinator:
+    PLUS { result = :DIRECT_ADJACENT_SELECTOR }
+  | GREATER { result = :CHILD_SELECTOR }
+  | TILDE { result = :FOLLOWING_SELECTOR }
+  | DOUBLESLASH { result = :DESCENDANT_SELECTOR }
+  | SLASH { result = :CHILD_SELECTOR }
+  ;
+
+  simple_selector:
+    element_name hcap_0toN {
+      result =  if val[1].nil?
+                  val[0]
+                else
+                  Node.new(:CONDITIONAL_SELECTOR, [val[0], val[1]])
+                end
+    }
+  | function
+  | function pseudo {
+      result = Node.new(:CONDITIONAL_SELECTOR, val)
+    }
+  | function attrib {
+      result = Node.new(:CONDITIONAL_SELECTOR, val)
+    }
+  | hcap_1toN {
+      result = Node.new(:CONDITIONAL_SELECTOR,
+        [Node.new(:ELEMENT_NAME, ['*']), val[0]]
+      )
+    }
+  ;
+
+  prefixless_combinator_selector:
+    combinator simple_selector_1toN {
+      result = Node.new(val[0], [nil, val[1]])
+    }
+  ;
+
+  simple_selector_1toN:
+    simple_selector combinator simple_selector_1toN {
+      result = Node.new(val[1], [val[0], val[2]])
+    }
+  | simple_selector S simple_selector_1toN {
+      result = Node.new(:DESCENDANT_SELECTOR, [val[0], val[2]])
+    }
+  | simple_selector
+  ;
+
+  class:
+    '.' IDENT { result = Node.new(:CLASS_CONDITION, [unescape_css_identifier(val[1])]) }
+  ;
+
+  element_name:
+    namespaced_ident
+  | '*' { result = Node.new(:ELEMENT_NAME, val) }
+  ;
+
+  namespaced_ident:
+    namespace '|' IDENT {
+      result = Node.new(:ELEMENT_NAME,
+        [[val[0], val[2]].compact.join(':')]
+      )
+    }
+  | IDENT {
+      name = @namespaces.key?('xmlns') ? "xmlns:#{val[0]}" : val[0]
+      result = Node.new(:ELEMENT_NAME, [name])
+    }
+  ;
+
+  namespace:
+    IDENT { result = val[0] }
+  |
+  ;
+
+  attrib:
+    LSQUARE attrib_name attrib_val_0or1 RSQUARE {
+      result = Node.new(:ATTRIBUTE_CONDITION,
+        [val[1]] + (val[2] || [])
+      )
+    }
+  | LSQUARE function attrib_val_0or1 RSQUARE {
+      result = Node.new(:ATTRIBUTE_CONDITION,
+        [val[1]] + (val[2] || [])
+      )
+    }
+  | LSQUARE NUMBER RSQUARE {
+      # non-standard, from hpricot
+      result = Node.new(:PSEUDO_CLASS,
+        [Node.new(:FUNCTION, ['nth-child(', val[1]])]
+      )
+    }
+  ;
+
+  attrib_name:
+    namespace '|' IDENT {
+      result = Node.new(:ATTRIB_NAME,
+        [[val[0], val[2]].compact.join(':')]
+      )
+    }
+  | IDENT {
+      # Default namespace is not applied to attributes.
+      # So we don't add prefix "xmlns:" as in namespaced_ident.
+      result = Node.new(:ATTRIB_NAME, [val[0]])
+    }
+  ;
+
+  function:
+    FUNCTION RPAREN {
+      result = Node.new(:FUNCTION, [val[0].strip])
+    }
+  | FUNCTION expr RPAREN {
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
+    }
+  | FUNCTION nth RPAREN {
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
+    }
+  | NOT expr RPAREN {
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
+    }
+  | HAS selector RPAREN {
+      result = Node.new(:FUNCTION, [val[0].strip, val[1]].flatten)
+    }
+  ;
+
+  expr:
+    NUMBER COMMA expr { result = [val[0], val[2]] }
+  | STRING COMMA expr { result = [val[0], val[2]] }
+  | IDENT COMMA expr { result = [val[0], val[2]] }
+  | NUMBER
+  | STRING
+  | IDENT {
+      case val[0]
+      when 'even'
+        result = Node.new(:NTH, ['2','n','+','0'])
+      when 'odd'
+        result = Node.new(:NTH, ['2','n','+','1'])
+      when 'n'
+        result = Node.new(:NTH, ['1','n','+','0'])
+      else
+        result = val
+      end
+    }
+  ;
+
+  nth:
+    NUMBER IDENT PLUS NUMBER          # 5n+3 -5n+3
+    {
+      if val[1] == 'n'
+        result = Node.new(:NTH, val)
+      else
+        raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
+      end
+    }
+  | IDENT PLUS NUMBER {               # n+3, -n+3
+      if val[0] == 'n'
+        val.unshift("1")
+        result = Node.new(:NTH, val)
+      elsif val[0] == '-n'
+        val[0] = 'n'
+        val.unshift("-1")
+        result = Node.new(:NTH, val)
+      else
+        raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
+      end
+    }
+  | NUMBER IDENT {                    # 5n, -5n, 10n-1
+      n = val[1]
+      if n[0, 2] == 'n-'
+        val[1] = 'n'
+        val << "-"
+        # b is contained in n as n is the string "n-b"
+        val << n[2, n.size]
+        result = Node.new(:NTH, val)
+      elsif n == 'n'
+        val << "+"
+        val << "0"
+        result = Node.new(:NTH, val)
+      else
+        raise Racc::ParseError, "parse error on IDENT '#{val[1]}'"
+      end
+    }
+  ;
+
+  pseudo:
+    ':' function {
+      result = Node.new(:PSEUDO_CLASS, [val[1]])
+    }
+  | ':' IDENT { result = Node.new(:PSEUDO_CLASS, [val[1]]) }
+  ;
+
+  hcap_0toN:
+    hcap_1toN
+  |
+  ;
+
+  hcap_1toN:
+    attribute_id hcap_1toN {
+      result = Node.new(:COMBINATOR, val)
+    }
+  | class hcap_1toN {
+      result = Node.new(:COMBINATOR, val)
+    }
+  | attrib hcap_1toN {
+      result = Node.new(:COMBINATOR, val)
+    }
+  | pseudo hcap_1toN {
+      result = Node.new(:COMBINATOR, val)
+    }
+  | negation hcap_1toN {
+      result = Node.new(:COMBINATOR, val)
+    }
+  | attribute_id
+  | class
+  | attrib
+  | pseudo
+  | negation
+  ;
+
+  attribute_id:
+    HASH { result = Node.new(:ID, [unescape_css_identifier(val[0])]) }
+  ;
+
+  attrib_val_0or1:
+    eql_incl_dash IDENT { result = [val[0], unescape_css_identifier(val[1])] }
+  | eql_incl_dash STRING { result = [val[0], unescape_css_string(val[1])] }
+  | eql_incl_dash NUMBER { result = [val[0], val[1]] }
+  |
+  ;
+
+  eql_incl_dash:
+    EQUAL           { result = :equal }
+  | PREFIXMATCH     { result = :prefix_match }
+  | SUFFIXMATCH     { result = :suffix_match }
+  | SUBSTRINGMATCH  { result = :substring_match }
+  | NOT_EQUAL       { result = :not_equal }
+  | INCLUDES        { result = :includes }
+  | DASHMATCH       { result = :dash_match }
+  ;
+
+  negation:
+    NOT negation_arg RPAREN {
+      result = Node.new(:NOT, [val[1]])
+    }
+  ;
+
+  negation_arg:
+    element_name
+  | element_name hcap_1toN
+  | hcap_1toN
+  ;
+
+  optional_S:
+    S
+  |
+  ;
+
 end
 
 ---- header