The source code

    /**
     * @ignore
     *  render for dialog
     * @author yiminghe@gmail.com
     */
    KISSY.add("overlay/dialog-render", function (S, OverlayRender,StdMod) {
        return OverlayRender.extend([
            StdMod
        ], {
            createDom: function () {
                var self = this,
                    el = self.get("el"),
                    id,
                    header = self.get("header");
                if (!(id = header.attr("id"))) {
                    header.attr("id", id = S.guid("ks-dialog-header"));
                }
                el.attr("role", "dialog")
                    .attr("aria-labelledby", id);
                // 哨兵元素，从这里 tab 出去到弹窗根节点
                // 从根节点 shift tab 出去到这里
                // tab catcher
                el.append("<div " + "t" + "ab" + "index='0' " +
                    // do not mess with main dialog
                    "style='position:absolute;'></div>");
            }
        });
    }, {
        requires: ['./overlay-render','./extension/stdmod-render']
    });