'Create a new ClassManager for a subclass of this ClassManager\'s
class.
This is called automatically when attributes are instrumented so that
the attributes can be propagated to subclasses against their own
class-local manager, without the need for mappers etc. to have already
pre-configured managers for the full class hierarchy.   Mappers
can post-configure the auto-generated ClassManager when needed.'

def _subclass_manager(self, cls):

    manager = manager_of_class(cls)
    if (manager is None):
        manager = _instrumentation_factory.create_manager_for_cls(cls)
    return manager
