docs: def serialize_on_parent(
              self,
              parent,  # type: ET.Element
              value,  # type: Any
              state  # type: _ProcessorState
      ):
          # type: (...) -> None
          """Serialize the value and adds it to the parent."""
          dict_value = self._converter.to_dict(value)
          self._dictionary.serialize_on_parent(parent, dict_value, state)