Since fragment identifier changes don't reload the page, state can be maintained in each of the frames.
This could be used to allow cross domain usage of an API that uses Comet as its communication with the server. Or for UI that a third party wants to embed it, but still allow some stateful communication with the hosting page.
- Communication is limited to the size of fragment identifiers. I'm not sure on the max size for all browsers, but I would think the same limitation on the size of GET URLs probably hold here too. So the max size for the full URL should probably be kept under around 1KB.
- Using the iframe may cause issues with the back button.