docs: def append(self, item):
          """ Appends the *item* to the end of the `Sequence`.
  
          :param item: any :class:`Structure`, :class:`Sequence`, :class:`Array`
              or :class:`Field` instance.
          """
          if not is_any(item):
              raise MemberTypeError(self, item, member=len(self))
          self._data.append(item)