def add_to_active_filters(cls, filter, key=None):
        """
        Add a new clause to the active filters. A filter may be either
        a Q object to be applied to the content class or a callable taking
        a queryset and spitting out a new one.

        If a filter with the given `key` already exists, the new filter
        replaces the old.
        """
        if cls.active_filters is None:
            cls.active_filters = {}
        if key is None:
            key = filter
        cls.active_filters[key] = filter

        Add a new clause to the active filters. A filter may be either
        a Q object to be applied to the content class or a callable taking
        a queryset and spitting out a new one.

        If a filter with the given `key` already exists, the new filter
        replaces the old.
        
feincms/utils/managers.py