canvas accessibility progress

Frank sent me a sample of canvas with a shadow DOM which I added aria live
region support for. The shadow DOM is exposed in the actual DOM but a
screen reader cannot speak it becuase it is not exposed to the
accessibility API. This is due to the fact that it is hidden.

So, the next step is to expose the shadow DOM. Alex Surkov is giving me a
time for when he can have a test patch that:

- exposes the shadow DOM to the accessibility API
- supports aria-activedescendant on canvas. This will allow the canvas
author to triger focus change events in the shadow DOM by simply modifying
the active id in the canvas element. This is low impact on the browser
rendering engine because they don't have to draw anything.

Frank, as soon as I get a patch or test build I will tell you how to get
it. Attached is my updated sample.

(See attached file: canvas-acc.html)

Rich

Rich Schwerdtfeger
Distinguished Engineer, SWG Accessibility Architect/Strategist