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The Alt/Object Problem [was: Re: media mix and universal connectedness]

From: Sean B. Palmer <sean@mysterylights.com>
Date: Tue, 18 Sep 2001 16:56:26 +0100
Message-ID: <018601c1405a$982e73e0$aeda93c3@y0r1d9>
To: <w3c-wai-gl@w3.org>
[+BCC to WAI PF, and W3C HTML Editor]

Summary: this mail raises (well-known) accessibility errors with the "alt"
attribute and "object" element, and suggests fixes.

"Al Gilman" <mailto:asgilman@iamdigex.net> wrote:-

> We are all in this together.  We can only all be connected if we
> use both words and pictures to connect.  Leave out either, and
> you have left out someone.

Al has established here that it is an acccessibility principle that content
of different modalities be used to "reinforce" the semantics of one
another, in order to reach a varied an audience is possible. The XML
Acccessibility Guidelines (XML GL), checkpoint 1.2 [1] introduces another
idiom that is very much related to this, one of "flexible associations". I
quote:-

[[[
For example, HTML lets you add "alt" to images, but it does not let you add
images to runs of text/markup, so people have to put up with less adequate
mechanisms, perhaps by adding "see figure 1" at the end of a paragraph.
]]]

XML GL raises this as an accessibility design error. Here, I want to
suggest methods of overcoming this. AFAICT, the alternatives to using "alt"
are:-

* Use <object>
* Wait for XHTML 2.0, where this problem will be fixed

In fact, <object> as-is is not an adequate flexible association mechanism,
because it cannot be explicitly linked to an alternative for the media
object, i.e. one that is external to the <object> element, rather than
appearing inside it. Also, <object> suffers from the "choice, not echo"
problem, in that nested objects *cascade* according to the HTML 4.01
specification:-

[[[
If a user agent cannot render the outermost OBJECT, it tries to render the
contents, which may be another OBJECT element, etc.
]]] - http://www.w3.org/TR/html401/struct/objects#edef-OBJECT

rather than being a pallette of choices, with some mark of indication that
there is an author preferred order.

I got to wondering how minor modifications/hacks could be made to HTML
4.01+ to overcome this problem. I've come up with two ideas that deserve to
be recorded:-

[[[
1) Use <label>/<div>

"label" is used to associate a run of markup with a form control, but could
be extended to associate a run of markup with a media object, viz. any
<img> or <object> elements that appear within it, or are linked to from the
"for" attribute specified by the HTML 4.01 specification.

The "div" element is also supposedly there to enbable us to group content
together, but it doesn't let us detail the semantics of the assoiation, and
it doesn't have a "for" attribute.

2) Use <a>

The "a" element is a standard HyperText link. It could be used, possibly in
conjenction with a "rel" attribute and profile to indicate that the
enclosed markup (%inline;) is associated with the media object as an
equivalent alternative.

Annoyingly, the "alt" attribute will still be required on the <img> element
even though there is a perfectly good alternative for it in the rest of the
document somewhere. Example (in XHTML):-

   <p><img src="img.png" alt="some alt" id="a" /></p>
   <p><a rel="alt" href="#a">Some good alt, perhaps with
     extra images, inline phrasing, ruby, and so on. A
     disadvantage to this is that you cannot nest links.</a></p>

All of which makes it a pointless hack.
]]]

Neither of these solutions are ideal. The problem still remains that people
have to resort to things like:-

   <p><img src="img.png" alt="some alt" id="a" /></p>
   <p><a href="#a">Diagram 1</a> shows xyz.</p>

With no way of getting rid of the alt attribute, or of indicating that the
alternative lies elsewhere. This is a serious accessibility error in HTML.

Conclusion: I favor (although am not happy about) waiting for XHTML 2.0 to
provide us with adequate equivalent/alterative mechanisms.

Cheers,

[1] http://www.w3.org/TR/2001/WD-xmlgl-20010829#cp1_2

--
Kindest Regards,
Sean B. Palmer
@prefix : <http://webns.net/roughterms/> .
:Sean :hasHomepage <http://purl.org/net/sbp/> .
Received on Tuesday, 18 September 2001 11:57:46 GMT

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