canvas accessibility: faked "shadow DOM" proof of concept

Last week at TPAC, I put together a faked "shadow DOM" proof of  
concept for the PFWG face-to-face meeting. I got a chance to work out  
the remaining bugs this morning, and promised Rich and Frank I'd send  
it to the list. The zip includes the demo as well as a copy of the  
Prototype JavaScript library that I used for event abstraction.

The demo was tested and works on Mac OS X 10.6 Snow Leopard, with  
Safari and a WebKit nightly. The WebKit nightly will provide a  
slightly better experience due to recent implementation of the WAI- 
ARIA presentation role. Keyboard access works in Firefox (tested  
v3.5.5), but Firefox doesn't yet have AX API support, so I had no way  
to test the accessibility. That said, I expect it will work as  
intended in Firefox on Windows.

Please view the comments in the HTML, CSS, and JavaScript for  
specifics on how it works now and is intended to work.

Thoughts?
James Craig