Thanks to Bill Budge for pointing me to State Charts.
I've been carefully sussing out the logic of Chrome's Fullscreen controller into a finite state machine, mainly so that we can get a group to agree on exactly what we think it should be doing. Chrome can go fullscreen in numerous ways: users entering and exiting via a menu or button, web pages making the transition (e.g. when you make a video fullscreen by clicking on it in a page), extensions, a special mode on Mac, and Windows 8 Metro Snap. Most of these include asynchronous transitions, and all API initiated transitions must be serviced (even if we're 'in the middle' of another transition).
Initially the diagram resembled a flying spaghetti monster, I've been winnowing it down discarding states we can design out of the naive total possibility space. But, it's also much simpler to notate using clustering and history offered in state charts.
BTW, state charts are also included in UML state machines.