docs: def _serialize(
              self,
              element,  # type: ET.Element
              value,  # type: Dict
              state  # type: _ProcessorState
      ):
          # type: (...) -> None
          """Serialize the dictionary and append all serialized children to the element."""
          for child in self._child_processors:
              state.push_location(child.element_path)
              child_value = value.get(child.alias)
              child.serialize_on_parent(element, child_value, state)
              state.pop_location()