The source code

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

        function Loading() {
        }

        Loading.prototype = {
            loading: function () {
                var self = this;
                if (!self._loadingExtEl) {
                    self._loadingExtEl = new Node("<div " +
                        "class='" +
                        self.get('prefixCls') + "ext-loading'" +
                        " style='position: absolute;" +
                        "border: none;" +
                        "width: 100%;" +
                        "top: 0;" +
                        "left: 0;" +
                        "z-index: 99999;" +
                        "height:100%;" +
                        "*height: expression(this.parentNode.offsetHeight);" + "'/>")
                        .appendTo(self.get("el"));
                }
                self._loadingExtEl.show();
            },

            unloading: function () {
                var lel = this._loadingExtEl;
                lel && lel.hide();
            }
        };

        return Loading;

    }, {
        requires: ['node']
    });