The source code

    /**
     * @ignore
     *  droppable for kissy
     * @author yiminghe@gmail.com
     */
    KISSY.add('dd/droppable', function (S, DD, Droppable, DroppableDelegate) {
        Droppable.Delegate = DroppableDelegate;
        DD.Droppable = Droppable;
        DD.DroppableDelegate = DroppableDelegate;
        return Droppable;
    }, { requires: ['dd/base', './droppable/base', './droppable/delegate'] });