@thomthom said:
Like AJAX solutions often do?
This approach is most often used for "inter-frame" communication. If there are 2 frames in a page that are hosted on different domains, the JS in one is not allowed to access the other, but many browsers allow you to change the fragment identifier regardless of security, so it might work in this case. (There are a handful of other mechanisms people have used to get around frame-2-frame security, and any of them might work. Searching on the topic might give us a clever workaround.)
Ajax apps will often modify the fragment to maintain state in the URL, so you can still email URLs around and have your friends land on the same "page" inside an Ajax app.