# File lib/xpath/expression.rb, line 128
      def to_xpath(predicate=nil)
        string = @expression
        string = @expression.to_xpath(predicate) unless @expression.is_a?(String)
        if string.include?("'")
          string = string.split("'", -1).map do |substr|
            "'#{substr}'"
          end.join(%q{,"'",})
          "concat(#{string})"
        else
          "'#{string}'"
        end
      end