Re: Please vote on the canvas accessibility proposal

Rich Schwerdtfeger
Distinguished Engineer, SWG Accessibility Architect/Strategist

public-html-a11y-request@w3.org wrote on 02/24/2010 04:06:31 AM:

> Ian Hickson <ian@hixie.ch>
> Sent by: public-html-a11y-request@w3.org
>
> 02/24/2010 04:06 AM
>
> To
>
> Steven Faulkner <faulkner.steve@gmail.com>
>
> cc
>
> Silvia Pfeiffer <silviapfeiffer1@gmail.com>, "public-html-
> a11y@w3.org" <public-html-a11y@w3.org>, public-canvas-api@w3.org
>
> Subject
>
> Re: Please vote on the canvas accessibility proposal
>
> On Wed, 24 Feb 2010, Steven Faulkner wrote:
> >
> > do you have any evidence to the contrary?
>
> The one <canvas> I use on a regular basis (not a demo) has accessible
> fallback and no adom="" attribute. Which is more common is essentially
> impossible to tell from purely anecdotal evidence.
>
>    http://www.whatwg.org/issues/data.html?period=1
>

Great. Set the role of <canvas> to an image and set aria-describedby to the
prose you have below it so that the AT and accessibility test tool know how
to test it.

What you have is in fact, semantically, a picture. Let the AT know it and
assess what the description is for it. Right now it is a drawing followed
by text. You are able to make a visual association where the blind user is
not. The blind user would need to guess.


>
> > >The point is that if the author doesn't care about conformance,
there's
> > >the possibility that the author will specify adom="" even if the
> > >content is inappropriate for ATs, and equally a possibility that the
> > >author will _not_ specify adom="" even if the content _is_ appropriate

> > >for ATs.
> >
> > how is the probability equal?
>
> I didn't say the probability was equal.
>
>
> > does any data support that attribute use follows this pattern of 50%
> > inappropriate use?
>
> Actually data for similar attributes -- longdesc="" and summary="" come
to
> mind -- show that the attributes are misused vastly more often than 50%
of
> the time.
>
>
> > there is data available to show that provision of accessible fallback
> > for canvas is pretty much zero.
>
> In demos. It's unclear what the right fallback would be when the whole
> point of the canvas is to show off the canvas for its own sake. Demos are

> not really representative here. (Arguably, "you don't have canvas" is
> actually the right thing to say in this case, in fact.)
>
>
> > >So adom="" is either redundant, or possibly inaccurate.
> >
> > how so?
>
> It's possibly inaccurate for authors who don't follow the spec, and it's
> unnecessary for those who do (since they can just make the page do the
> right thing in both cases).
>
>
> > I can foresee instances where the developer provides an accessible
> > alternative outside of the canvas (currently conforming no?) and wants
to
> > tell users of browsers that don't support canvas that they are missing
> > something:
> >
> > <canvas> you cannot see the graph because your browser does not support
> > canvas </canvas>
> > <!-- table containing data represented in graph -->
>
> In this case, if canvas is available, then the author can trivially just
> remove the contents of the canvas in one line of code. adom="" isn't
> useful for hiding this text.
>
> --
> Ian Hickson               U+1047E                )\._.,--....,'``.    fL
> http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
> Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'
>