Example canvas element use - accessibility concerns

The recently released code editor Bespin (
https://bespin.mozilla.com/index.html) is a great example of the utility of
the canvas element, its also a worrying example of the barriers to
accessibility its use will produce. It includes editable text, folder lists
and interactive elements that are all essentially a graphic. there does not
appear to be a way to extract any usable information to support Assistive
technology to interpret or provide interaction.

The current advice on its use and provision of fallback content seems
somewhat weak given the example of its use in Bespin:

"Authors should not use the
canvas<http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element>element
in a document when a more suitable element is available. For
example, it is inappropriate to use a
canvas<http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element>element
to render a page heading: if the desired presentation of the heading
is graphically intense, it should be marked up using appropriate elements
(typically h1<http://www.w3.org/TR/html5/semantics.html#the-h1-h2-h3-h4-h5-and-h6-elements>)
and then styled using CSS and supporting technologies such as XBL.

When authors use the
canvas<http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element>element,
they should also provide content that, when presented to the user,
conveys essentially the same function or purpose as the bitmap canvas. This
content may be placed as content of the
canvas<http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element>element.
The contents of the
canvas<http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element>element,
if any, are the element's fallback
content <http://www.w3.org/TR/html5/dom.html#fallback-content>." [1]
Are there plans to provide mechanisms to add accessibility hooks for content
produced using canvas? As providing a secondary accessible version of an
application such as bespin seems like a non starter, and is a prime example
of the sort of "bolt on" accessibility that HTML5 was trying to move away
from.

[1] http://www.w3.org/TR/html5/the-canvas-element.html#the-canvas-element

-- 
with regards

Steve Faulkner
Technical Director - TPG Europe
Director - Web Accessibility Tools Consortium

www.paciellogroup.com | www.wat-c.org
Web Accessibility Toolbar -
http://www.paciellogroup.com/resources/wat-ie-about.html