Cross-browser communication with an iframe using the splendid fragment identifier hack. The frame is the coloured block containing the speed up/down buttons and comes from a different domain (ajaxpatterns.org). We *send* colour info *towards* that domain by setting the frame's fragment identifier to the desired colour (the frame has a script polling its frag identifier). We *receive* speed info *from* that domain by polling the main page fragment identifier.
The hack relies on the fact that a page can change its child frame's URL and a child frame can change its parent's URL (which is incidentally how it can avoid being 'trapped' - by simply reloading itself in the entire main page, accessing parent.window.location....). (PS the lift/elevator is some gratuitous fun - I wanted something more than just a log message back and forth!)