def METHOD_NAME(event, graph, handler, target, dispatcher):
    """ Handler for maintaining observers. Used by ObserverChangeNotifier.
    Parameters
    ----------
    event : SetChangeEvent
        Change event that triggers the maintainer.
    graph : ObserverGraph
        Description for the *downstream* observers, i.e. excluding self.
    handler : callable
        User handler.
    target : object
        Object seen by the user as the owner of the observer.
    dispatcher : callable
        Callable for dispatching the handler.
    """
    for removed_item in event.removed:
        add_or_remove_notifiers(
            object=removed_item,
            graph=graph,
            handler=handler,
            target=target,
            dispatcher=dispatcher,
            remove=True,
        )
    for added_item in event.added:
        add_or_remove_notifiers(
            object=added_item,
            graph=graph,
            handler=handler,
            target=target,
            dispatcher=dispatcher,
            remove=False,
        )