[simonw]

It's not impossible though. One method of doing that is to use the trick where an iframe can communicate with its parent document by altering the #fragment URL, which can be read by both parties. It's dirty but it works. The new HTML5 postMessage API can be used as an alternative for browsers that support it.

[alanh]

I didn’t even realize postMessage was a new API. It works in everything newer than IE7. http://caniuse.com/#x-doc-messaging