The Main Event - event oriented programming in Maya

The Maya Callbacks Cheat Sheet post started out as an effort to explain the design the event system in mGui - but it quickly turned into it's own thing as I realized that the vanilla Maya system remains confusing to lots of people.  With that background out of the way, I want to return to events proper, both to explain why they work the way the do in mGui and also how they can be useful for other projects as well (I use them all over the place in non-GUI contexts).

...and, because it's got the word 'event' in it, I'm going to throw in a lot of irrelevant references as I can manage to The Crushah!