The source code

    /**
     * @ignore
     *  loading mask support for overlay
     * @author yiminghe@gmail.com
     */
    KISSY.add("overlay/extension/loading", function () {

        /**
         * @class KISSY.Overlay.Extension.Loading
         * Loading extension class. Make component to be able to mask loading.
         */
        function Loading() {
        }

        Loading.prototype = {
            /**
             * mask component as loading
             * @chainable
             */
            loading: function () {
                var self=this;
                self.get("view").loading();
                return self;
            },

            /**
             * unmask component as loading
             * @chainable
             */
            unloading: function () {
                this.get("view").unloading();
                return this;
            }
        };

        return Loading;

    });