def append_class (cls)
      return unless cls

      if c = html_options["class"]
        html_options["class"] << " " + cls.to_s
      else
        if c = has_option?("class")
          c << " " + cls.to_s
          cls = c
        end

        html_options["class"] = cls.to_s
      end
    end
def append_class (cls)
      return unless cls

      if c = html_options["class"]
        html_options["class"] << " " + cls.to_s
      else
        if c = has_option?("class")
          c << " " + cls.to_s
          cls = c
        end

        html_options["class"] = cls.to_s
      end
    end
Appends the given class to the "class" HTMl attribute.

 @param cls [String, Symbol] the class to append