Ah...the newly updated file is still propagating on our servers.
In the meantime, you can just edit your local copy of the
JS file. I posted the code change I made to the handler object directly in the example page. You can see the extra HTML markup and closing of the iframe tag:
app.setContent("<iframe name=\"tabiframe-app\" src=\"http://www.yahoo.com/\" width=\"100%\" height=\"100%\" /></iframe>"); // write HTML to app
ZCS 6.0:Zimlet Developers Guide:Examples:Tab iFrame - Zimbra :: Wiki