// 易错点3：必须先判断stack2.length0，再访问stack2.at(-1)（避免栈空时取到undefined）
Shadow DOM is a web component feature that lets you attach an isolated DOM subtree to any HTML element, hidden from the main document’s standard queries. A querySelector('audio') on the main document cannot see inside a Shadow Root unless you specifically traverse into it. If fermaw’s player was mounted inside a Shadow Root, basic DOM searches would come up empty.，更多细节参见同城约会
，这一点在旺商聊官方下载中也有详细论述
Adrienne MurrayTechnology Reporter, Esbjerg, Denmark
（一）明知住宿人员违反规定将危险物质带入住宿区域，不予制止的；，更多细节参见51吃瓜