'Returns a list of plugin types that can be added
as children to this plugin.'

@classmethod
def get_child_classes(cls, slot, page, instance=None):

    child_classes = cls.get_child_class_overrides(slot, page)
    if child_classes:
        return child_classes
    installed_plugins = cls.get_child_plugin_candidates(slot, page)
    child_classes = []
    plugin_type = cls.__name__
    for plugin_class in installed_plugins:
        allowed_parents = plugin_class.get_parent_classes(slot, page, instance)
        if ((not allowed_parents) or (plugin_type in allowed_parents)):
            child_classes.append(plugin_class.__name__)
    return child_classes
