@classmethod
def _SetSupersedingClass(cls, superseding):
    """Set the class reference attribute.

        @param superseding: A Python class that is a subclass of this class.
        """
    assert superseding is None or issubclass(superseding, cls)
    if superseding is None:
        cls.__dict__.pop(cls.__SupersedingClassAttribute(), None)
    else:
        setattr(cls, cls.__SupersedingClassAttribute(), superseding)
    return superseding
