The source code

    /**
     * @ignore
     * 里层包裹层定义， 适合mask以及shim
     * @author yiminghe@gmail.com
     */
    KISSY.add("component/extension/content-box-render", function (S, Node, DOM) {

        function ContentBoxRender() {
        }

        ContentBoxRender.ATTRS = {
            contentEl: {
                // 不写 valueFn, 留待 createDom 处理
            }
        };

        /*
         ! contentEl 只能由组件动态生成
         */
        ContentBoxRender.prototype = {
            __createDom: function () {
                var self = this,
                    contentEl,
                    el = self.get("el"),
                    childNodes = el[0].childNodes,
                    c = childNodes.length && DOM._nodeListToFragment(childNodes);

                // 产生新的 contentEl
                contentEl = Node.all("<div class='" +
                    self.get('prefixCls') + "contentbox'>" +
                    "</div>");

                if (c) {
                    contentEl.append(c);
                }

                el.append(contentEl);

                self.setInternal("contentEl", contentEl);
            }
        };

        return ContentBoxRender;
    }, {
        requires: ["node", 'dom']
    });