W3C home > Mailing lists > Public > public-bpwg@w3.org > November 2009

Re: ACTION-885 (Canvas)

From: Alan Chuter <achuter@technosite.es>
Date: Mon, 23 Nov 2009 14:12:31 +0100
Message-ID: <4B0A8A3F.2050801@technosite.es>
To: Public BPWG <public-bpwg@w3.org>
CC: achuter@technosite.es
I would like to emphasise that my comments on this matter (of some weeks 
ago now) should not be taken to call for any changes to the document and 
I do not expect them to be addressed by the group.

best regards,


Alan Chuter wrote:
> 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 Monday, 23 November 2009 13:16:36 UTC

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