# File lib/nokogiri/css/parser.rb, line 46
      def xpath_for string, options={}
        v = self.class[string]
        return v if v

        prefix = options[:prefix] || nil
        visitor = options[:visitor] || nil
        args = [prefix, visitor]
        self.class[string] = parse(string).map { |ast|
          ast.to_xpath(prefix, visitor)
        }
      end