# File lib/nokogiri/css/node.rb, line 19
      def preprocess!
        ### Deal with nth-child
        matches = find_by_type(
          [:CONDITIONAL_SELECTOR,
            [:ELEMENT_NAME],
            [:PSEUDO_CLASS,
              [:FUNCTION]
            ]
          ]
        )
        matches.each do |match|
          if match.value[1].value[0].value[0] =~ /^nth-child/
            tag_name = match.value[0].value.first
            match.value[0].value = ['*']
            match.value[1] = Node.new(:COMBINATOR, [
              match.value[1].value[0],
              Node.new(:FUNCTION, ['self(', tag_name])
            ])
          end
          if match.value[1].value[0].value[0] =~ /^nth-last-child/
            tag_name = match.value[0].value.first
            match.value[0].value = ['*']
            match.value[1] = Node.new(:COMBINATOR, [
              match.value[1].value[0],
              Node.new(:FUNCTION, ['self(', tag_name])
            ])
          end
        end

        ### Deal with first-child, last-child
        matches = find_by_type(
          [:CONDITIONAL_SELECTOR,
            [:ELEMENT_NAME], [:PSEUDO_CLASS]
        ])
        matches.each do |match|
          if ['first-child', 'last-child'].include?(match.value[1].value.first)
            which = match.value[1].value.first.gsub(/-\w*$/, '')
            tag_name = match.value[0].value.first
            match.value[0].value = ['*']
            match.value[1] = Node.new(:COMBINATOR, [
              Node.new(:FUNCTION, ["#{which}("]),
              Node.new(:FUNCTION, ['self(', tag_name])
            ])
          elsif 'only-child' == match.value[1].value.first
            tag_name = match.value[0].value.first
            match.value[0].value = ['*']
            match.value[1] = Node.new(:COMBINATOR, [
              Node.new(:FUNCTION, ["#{match.value[1].value.first}("]),
              Node.new(:FUNCTION, ['self(', tag_name])
            ])                                        
          end
        end

        self
      end