显然，Chrome允许使用名为 allow-popups 。该属性在Firefox中也受支持，并且是 W3C 。

Apparently Chrome allows an undocumented sandbox property called allow-popups to be set. The property is also supported in Firefox and is a Candidate Recommendation on W3C.

allow-popups 让沙盒框架在新窗口或标签中打开链接并且，看起来，当框架尝试打开 target =_ top的链接时，浏览器将在新选项卡或窗口中打开URL。

allow-popups lets the sandboxed frame open links in new windows or tabs and, it appears, when the frame tries to open a link with target="_top" the browser will open the URL in a new tab or window.