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Re: Proposal for <canvas src> to allow images with structured fallback by Tab Atkins Jr.

From: Tab Atkins Jr. <jackalmage@gmail.com>
Date: Thu, 10 Mar 2011 15:01:38 -0800
Message-ID: <AANLkTi=8rxN8gVzYf4wU1OP6db82tjR+zjSMDpRNqt_=@mail.gmail.com>
To: Richard Schwerdtfeger <schwer@us.ibm.com>
Cc: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>, Steve Faulkner <faulkner.steve@gmail.com>, Laura Carlson <laura.lee.carlson@gmail.com>, HTML WG LIST <public-html@w3.org>, HTML Accessibility Task Force <public-html-a11y@w3.org>, public-html-request@w3.org
On Thu, Mar 10, 2011 at 2:51 PM, Richard Schwerdtfeger
<schwer@us.ibm.com> wrote:
> So, we discussed this on the html accessibility call today.
> The concern about using canvas to do this is that for canvas accessibility we have a one for one mapping between the fallback content and the corresponding visual renderings on the physical canvas. It sounds like what people are asking for is the ability to associate rich descriptive content for an image. If we were to use that as the fallback content we would totally hose ATs who expect the content to be a one for one mapping.
> One of the things we did in XHTML 2 was to use the fallback content of <img> and <object> to provide this augmented content. Here you would use the fallback content to provide the equivalent of a long description. Something on the order of:
> <img src="eiffeltower.jpg">
> This is a picture of the Eiffel tower. The tower is composed of ... The tower is open from ...
> <h1>Entrance Fees</h1>
> The tower entrance fees are as follows:
> <table>
> <th> ....
> </table>
> </img>
> Is this what you were thinking of? I mean, we could do this for <img> and <obj>

If the page is *extremely* badly authored such that all of that
content is exposed to sighted users via the image, then sure.  The
fallback content should still be a one-to-one replacement.

I would hope that we still *strongly* advocate against such horrible
usability.  Having all that information exposed solely as an image
means that sighted users can't copypaste or find-in-page on it, etc..

In general, actual content should still be in the normal page,
accessible to all users.  Rich fallback (like what @longdesc and
<canvas src> are designed to expose) should only be necessary in rare
circumstances, when the author has a particularly information-dense
graphic for some reason, like a webcomic or a chart.

Received on Thursday, 10 March 2011 23:02:31 UTC

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