docs: def extra(self, value, extra_name, default=None):
          """
          Get the additional enumeration value for ``extra_name``.
  
          :param unicode value: Enumeration value.
          :param str extra_name: Extra name.
          :param default: Default value in the case ``extra_name`` doesn't exist.
          """
          try:
              return self.get(value).get(extra_name, default)
          except InvalidEnumItem:
              return default