code: def append_attribute(self, name, value, content):
          
          key = name
          key = '_%s' % reserved.get(key, key)
          setattr(content.data, key, value)
docs: Append an attribute name/value into L{Content.data}.
          @param name: The attribute name
          @type name: basestring
          @param value: The attribute's value
          @type value: basestring
          @param content: The current content being unmarshalled.
          @type content: L{Content}