Cross-domain JavaScript code with sibling sub-domains

Question

I have two web applications setups:

david.example.com and john.example.com

David opens a new window to John:

Answer 1

You can always use iframes for cross domain communication and send messages via the hashbangs. See this for an example. It's basically the workings of stuff like Facebook connect. If one app opens the other window I'm guessing you can do that with normal windows as well.