What are the benefits to using iframes for ajax long polling?

What are the benefits of using ifra开发者_C百科mes for Comet long polling? Why not just keep an asynchronous ajax request in a script file pulled into the main page? Thanks.

It makes portability to IE possible: http://softwareas.com/portable-comet-its-the-iframe-stupid

Also, some people use it as a security feature. Within an iFrame you can enclose everything within a JavaScript closure and improve your security. There are better ideas for security though.

• http://code.google.com/p/google-caja/
• http://www.adsafe.org/