def format
      raise FormatError.new(self) unless formattable?

      REXML::Element.new(type).tap do |attribute|
        attribute.attributes["key"] = @key
        attribute.attributes["value"] = format_value
        meta.each {|m| attribute.elements << m.format if m.formattable?}
      end
    end
def format
      raise FormatError.new(self) unless formattable?

      REXML::Element.new(type).tap do |attribute|
        attribute.attributes["key"] = @key
        attribute.attributes["value"] = format_value
        meta.each {|m| attribute.elements << m.format if m.formattable?}
      end
    end
Format as a XML element.