# File lib/capybara/xpath.rb, line 159
    def extract_postfix(options)
      options.inject("") do |postfix, (key, value)|
        case key
          when :value     then postfix += "[@value=#{s(value)}]"
          when :text      then postfix += "[text()=#{s(value)}]"
          when :checked   then postfix += "[@checked]"
          when :unchecked then postfix += "[not(@checked)]"
          when :options   then postfix += value.map { |o| "[.//option/text()=#{s(o)}]" }.join
          when :selected  then postfix += [value].flatten.map { |o| "[.//option[@selected]/text()=#{s(o)}]" }.join
        end
        postfix
      end
    end