preprocess! (Nokogiri::CSS::Node)

    # File lib/nokogiri/css/node.rb, line 28
          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