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Re: ISSUE-30 longdesc - Chairs Solicit Alternate Proposals or Counter-Proposals

From: Matthew Turvey <mcturvey@gmail.com>
Date: Wed, 15 Jun 2011 10:21:45 +0100
Message-ID: <BANLkTima1DTkNEo+CcbcLzcFpS-H-Ksm9w@mail.gmail.com>
To: HTML WG LIST <public-html@w3.org>
Cc: Jonas Sicking <jonas@sicking.cc>, janina@rednote.net
On 15 June 2011 03:08, Janina Sajka <janina@rednote.net> wrote:
[..]
> On behalf of the Text Subteam of the HTML-A11Y Task Force,
>
> We believe an ARIA approach for providing long text descriptions of
> images will necessarily fall short on several key requirements today.
> Therefore, we will be reading your CP with particular interest regarding
> how you adress the following three specific requirements which are of
> particular concern to us:
>
> 1.)     Backward Compatibility
>
>        We believe it is important to support users with older
>        technologies in this feature. The CP we backed does this, and we
>        are keenly concerned that the approach adopted for HTML 5 do
>        so as well.
>
>        http://www.w3.org/html/wg/wiki/ChangeProposals/InstateLongdesc
>        http://lists.w3.org/Archives/Public/public-html/2011May/0170.html
>
> 2.)     Display content only upon user request
>
>        A key behavioral requirement for this feature is that the
>        content of the long text description is displayed/voiced ONLY
>        when the user requests it. In other words users need to know
>        that a longer textual description is available, and they need to
>        be able to easily request that content be presented to them--or
>        not. In no instance, however, should such content be
>        automatically displayed, as alt text is automatically displayed.
>        This behavioral distinction is one key distinction between the
>        required short and long text description mechanisms as described
>        by WAI at:
>
>        http://www.w3.org/2009/06/Text-Alternatives-in-HTML5.html
>
> 3.)     Provide a reliable and effective user experience
>
>        Inasmuch as ARIA is new technology not yet fully or consistently
>        implemented by browsers or AT, how will you propose that your
>        ARIA based long text description can serve users needs
>        effectively and consistently, regardless of what particular
>        browser or particular AT a user may employ? In asking this
>        question we note that the CP we have endorsed DOES provide
>        effective and consistent support for users regardless of browser
>        and AT, and we believe they deserve that kind of support.
>
>
> To reiterate our concern--these are three requirements we consider
> essential to a long text description mechanism which we don't believe
> can currently be met using ARIA technology,

I don't think it is entirely accurate to say that longdesc currently
provides a reliable and effective user experience, or has effective
and consistent support.

longdesc is not implemented in Orca or VoiceOver so is currently
inaccessible by default to entire platforms. It is also inaccessible
by default to IE, Firefox, Chrome or Safari users, and NVDA, ZoomText,
etc AT users etc. longdesc also has a history of authoring and
usability problems (see previous CPs).

aria-describedby is more backward compatible than longdesc, because
UAs that don't support it can still access the elements referenced by
aria-describedby i.e. it is more robust. In contrast londesc links are
completely inaccessible in UAs and AT that do not support it.

So:

1) longdesc is not backward- or currently-compatible with some
existing UAs and AT

2) most users, including some SR users, cannot currently display
longdesc content at all

3) longdesc needs improved UA and AT support, and author/user
training, before it can provide a reliable and effective user
experience

I'll also note WAI-CG accepted obsoleting longdesc in HTML5 if aria
was incorporated into the spec, and aria-describedby was spec'ed to
support links, which it is:

http://www.w3.org/2009/06/Text-Alternatives-in-HTML5
http://www.w3.org/TR/wai-aria-implementation/#mapping_additional_relations

My understanding is that this issue is still being discussed because
some PFWG members, quoting Sam, think "we need more time to properly
deprecate longdesc":

http://lists.w3.org/Archives/Public/public-html-a11y/2011Apr/0181.html

but since longdesc is not currently widely supported and must
currently be accompanied by an alternative technique to ensure
accessibility, this does not seem necessary. longdesc will continue to
be exposed in the DOM by browsers as it is now:

http://www.w3.org/TR/html5/obsolete.html#dom-img-longdesc

So it seems the only drawback of obsoleting longdesc in HTML5 is that
the few sites currently using longdesc will see a conformance error if
they ever check their pages - which would hopefully encourage them to
switch to a more accessible technique anyway.

I'd like to suggest that the HTML-A11Y Task Force's longdesc CP be
withdrawn by amicable consensus so we don't have to spend any more
time on this issue.

-Matt
Received on Wednesday, 15 June 2011 09:22:25 UTC

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