code: def extend(self, elem_seq):
      
  
      if elem_seq is None:
        return
      try:
        elem_seq_iter = iter(elem_seq)
      except TypeError:
        if not elem_seq:
          # silently ignore falsy inputs :-/.
          # TODO(ptucker): Deprecate this behavior. b/18413862
          return
        raise
  
      new_values = [self._type_checker.CheckValue(elem) for elem in elem_seq_iter]
      if new_values:
        self._values.extend(new_values)
      self._message_listener.Modified()
docs: Extends by appending the given iterable. Similar to list.extend().