Ease of testing canvas accessible subtree (was: Re: Integration of HTM)

Henri Sivonen wrote:
> As for the accessible DOM subtree in canvas, I think it'll be
> challenging enough to get authors to provide the subtree at all and
> to keep it in sync with the canvas rendering that complicating things
> by adding multiple alternative subtrees isn't helpful.

In the current spec, it seems like this is harder than it should be. For 
  drawFocusRing to work, the HTML elements that reflect the same 
application state as the canvas bitmap must be descendants of the 
<canvas> element. In interactive visual media (hence in the web browsers 
that most authors will develop and test their site with), these 
descendants will never get rendered.

To develop and test an accessible canvas application with focus 
management, I'd expect it would be much easier if the author could see 
the bitmap and the fallback content simultaneously, using their normal 
mouse and keyboard input to interact with either version, and check that 
both representations stay in sync and that the focus highlighting is 
handled correctly. Once they've finished testing, they would want the 
published version to work like it currently does (i.e. users are shown 
the bitmap if possible, else the fallback content is shown instead).

Is this possible with the current spec? If not, I think there should be 
a way to make the fallback content and bitmap visible together, e.g. 
<canvas showfallback>...</canvas> (and authors can add some CSS to the 
fallback content so it's rendered in a sensible position), to help with 
this kind of testing.

Philip Taylor

Received on Friday, 5 February 2010 15:55:46 UTC