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Re: ACTION-885 (Canvas)

From: Alan Chuter <achuter@technosite.es>
Date: Tue, 03 Nov 2009 17:17:41 +0100
Message-ID: <4AF057A5.1030004@technosite.es>
To: Public BPWG <public-bpwg@w3.org>
CC: Henny Swan <hennys@opera.com>, Yeliz Yesilada <yesilady@cs.man.ac.uk>
The document says "Canvas ... is not inherently accessible and so should 
not be used as the sole means of conveying information." [1]

Perhaps the word "alternative" is needed here, "If you need to use 
canvas, then provide an alternative."

I think that as this is about dynamic graphics the document should also 
add the proviso that the alternative should be updated as the image is 
redrawn, if that changes its meaning. How this is done in canvas I don't 
know, probably by the same script that updates the image. Updates to the 
DOM (which would be used for the alternative) are detected by some 
current mobile screen readers. This also applies to SVG. SVG supports 
accessibility but in practice it requires a text alternative for the 
whole image.

Another solution might be to require that it be used in an 
accessibility-supported way, as defined by WCAG [2].

[1] http://www.w3.org/TR/mwabp/#bp-canvas
[2] http://www.w3.org/TR/WCAG20/#accessibility-supporteddef

Alan Chuter
Departamento de Usabilidad y Accesibilidad
Technosite - Grupo Fundosa
FundaciĆ³n ONCE
Tfno.: 91 121 03 30
Fax: 91 375 70 51
Received on Tuesday, 3 November 2009 16:21:28 UTC

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