Okay, so I feel a bit stupid for not having noticed this before. I wanted to geo-tag my blog in FeedBurner and so flicked to Google Maps to work out the latitude and longitude of the head office of the company at which I work.
For the record, the code works, but that's not what caught my attention. The code runs, but the part that was new to me is that the code runs in the context of the current browser window and has access to all its variables. I'd never realised that before, hence why I now feel stupid.
Oh, and yes, jQuery expressions do work, but watch out for characters requiring escaping in your selectors.
 I'm Australian. That's correct spelling. So there :)