W3C home > Mailing lists > Public > public-html-a11y@w3.org > May 2011

Re: Moving longdesc forward

From: Geoff Freed <geoff_freed@wgbh.org>
Date: Wed, 4 May 2011 08:28:23 -0400
To: Leif Halvard Silli <xn--mlform-iua@xn--mlform-iua.no>, Benjamin Hawkes-Lewis <bhawkeslewis@googlemail.com>
CC: Laura Carlson <laura.lee.carlson@gmail.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
Message-ID: <C9E6BEA7.5F21%geoff_freed@wgbh.org>

A couple of comments below.
Geoff Freed

On 5/4/11 8:04 AM, "Leif Halvard Silli" <xn--mlform-iua@xn--mlform-iua.no> wrote:

Leif Halvard Silli, Wed, 4 May 2011 13:20:35 +0200:
>> Since a single URL can serve multiple formats, on the user agent side, we'd
>> need to add a requirement that the URL be requested using an Accept header
>> giving a higher quality value to the desired media types.
> For @src of the IMG element, then HTML5 gives a very specific list. Is
> that list linked to use of an accept header?
> http://dev.w3.org/html5/spec/embedded-content-1.html#the-img-element

A starting point is to say what it should *not* be. Namely, it should
not be any of the formats that can validly be placed inside the img@src
attribute. This is what HTML5 says about @src:

Images can thus be static bitmaps (e.g. PNGs, GIFs, JPEGs), single-page
vector documents (single-page PDFs, XML files with an SVG root
element), animated bitmaps (APNGs, animated GIFs), animated vector
graphics (XML files with an SVG root element that use declarative SMIL
animation), and so forth. However, this also precludes SVG files with
script, multipage PDF files, interactive MNG files, HTML documents,
plain text documents, and so forth.

It should also not be video files, audio files etc. AUthors are *not*
prevented from including video or audio in their longdesc documents -
they only have to make sure they use a <video> element, <audio>
element. Etc.

I agree with what you say about longdesc delivered via accessible video or audio- embed clips in a structured page using the appropriate element.

May be, w.r.t. 'structured host language', we could learn from the @src
definition and say that longdesc resources should be located inside
'HTML and XML files with <html> as root element'.

I'd be hesitant to put this restriction place because in some cases it imposes an extra step on the user.  For example, if I want to use a plain-text document, or an accessible PDF, to deliver my longdesc, are you saying that I must first lead users to a structured document from which they select a link that *then* leads to the plain-text/PDF longdesc?
Received on Wednesday, 4 May 2011 12:30:52 UTC

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