    # File lib/nokogiri/css/generated_tokenizer.rb, line 44
      def scan_evaluate( str )
        scan_setup
        @rex_tokens = []
        @lineno  =  1
        ss = StringScanner.new(str)
        state = nil
        until ss.eos?
          text = ss.peek(1)
          @lineno  +=  1  if text == "\n"
          case state
          when nil
            case
            when (text = ss.scan(/[-@]?([_A-Za-z]|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])([_A-Za-z0-9-]|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])*\(\s*/))
               @rex_tokens.push action { [:FUNCTION, text] }

            when (text = ss.scan(/[-@]?([_A-Za-z]|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])([_A-Za-z0-9-]|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])*/))
               @rex_tokens.push action { [:IDENT, text] }

            when (text = ss.scan(/\#([_A-Za-z0-9-]|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])+/))
               @rex_tokens.push action { [:HASH, text] }

            when (text = ss.scan(/[\s\r\n\f]*~=[\s\r\n\f]*/))
               @rex_tokens.push action { [:INCLUDES, text] }

            when (text = ss.scan(/[\s\r\n\f]*\|=[\s\r\n\f]*/))
               @rex_tokens.push action { [:DASHMATCH, text] }

            when (text = ss.scan(/[\s\r\n\f]*\^=[\s\r\n\f]*/))
               @rex_tokens.push action { [:PREFIXMATCH, text] }

            when (text = ss.scan(/[\s\r\n\f]*\$=[\s\r\n\f]*/))
               @rex_tokens.push action { [:SUFFIXMATCH, text] }

            when (text = ss.scan(/[\s\r\n\f]*\*=[\s\r\n\f]*/))
               @rex_tokens.push action { [:SUBSTRINGMATCH, text] }

            when (text = ss.scan(/[\s\r\n\f]*!=[\s\r\n\f]*/))
               @rex_tokens.push action { [:NOT_EQUAL, text] }

            when (text = ss.scan(/[\s\r\n\f]*=[\s\r\n\f]*/))
               @rex_tokens.push action { [:EQUAL, text] }

            when (text = ss.scan(/[\s\r\n\f]*\)/))
               @rex_tokens.push action { [:RPAREN, text] }

            when (text = ss.scan(/[\s\r\n\f]*\[[\s\r\n\f]*/))
               @rex_tokens.push action { [:LSQUARE, text] }

            when (text = ss.scan(/[\s\r\n\f]*\]/))
               @rex_tokens.push action { [:RSQUARE, text] }

            when (text = ss.scan(/[\s\r\n\f]*\+[\s\r\n\f]*/))
               @rex_tokens.push action { [:PLUS, text] }

            when (text = ss.scan(/[\s\r\n\f]*>[\s\r\n\f]*/))
               @rex_tokens.push action { [:GREATER, text] }

            when (text = ss.scan(/[\s\r\n\f]*,[\s\r\n\f]*/))
               @rex_tokens.push action { [:COMMA, text] }

            when (text = ss.scan(/[\s\r\n\f]*~[\s\r\n\f]*/))
               @rex_tokens.push action { [:TILDE, text] }

            when (text = ss.scan(/\:not\([\s\r\n\f]*/))
               @rex_tokens.push action { [:NOT, text] }

            when (text = ss.scan(/-?([0-9]+|[0-9]*\.[0-9]+)/))
               @rex_tokens.push action { [:NUMBER, text] }

            when (text = ss.scan(/[\s\r\n\f]*\/\/[\s\r\n\f]*/))
               @rex_tokens.push action { [:DOUBLESLASH, text] }

            when (text = ss.scan(/[\s\r\n\f]*\/[\s\r\n\f]*/))
               @rex_tokens.push action { [:SLASH, text] }

            when (text = ss.scan(/U\+[0-9a-f?]{1,6}(-[0-9a-f]{1,6})?/))
               @rex_tokens.push action {[:UNICODE_RANGE, text] }

            when (text = ss.scan(/[\s\t\r\n\f]+/))
               @rex_tokens.push action { [:S, text] }

            when (text = ss.scan(/"([^\n\r\f"]|\n|\r\n|\r|\f|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])*"|'([^\n\r\f']|\n|\r\n|\r|\f|[^\0-\177]|\\[0-9A-Fa-f]{1,6}(\r\n|[\s\n\r\t\f])?|\\[^\n\r\f0-9A-Fa-f])*'/))
               @rex_tokens.push action { [:STRING, text] }

            when (text = ss.scan(/./))
               @rex_tokens.push action { [text, text] }

            else
              text = ss.string[ss.pos .. -1]
              raise  ScanError, "can not match: '" + text + "'"
            end  # if

          else
            raise  ScanError, "undefined state: '" + state.to_s + "'"
          end  # case state
        end  # until ss
      end