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RE: Alt is not a description (was Re: when to use longdesc for images)

From: John M Slatin <john_slatin@austin.utexas.edu>
Date: Tue, 21 Dec 2004 09:10:40 -0600
Message-ID: <6EED8F7006A883459D4818686BCE3B3B2906CE@MAIL01.austin.utexas.edu>
To: "Tina Holmboe" <tina@greytower.net>, <w3c-wai-ig@w3.org>

This is a healthy discussion! I know it refers to WCAG 1.0, the current normative reference, but I thought people on the list might be interested in related discussions around WCAG 2.0.

The WCAG Working Group has also been discussing the characteristics of good alt text, in the context of developing testable success criteria and the tests that will help to determine conformance.

The wording most recently approved for Guideline 1.1 Level 1 Success Criterion 1 reads as follows:

1. For all non-text content that is functional, such as graphical links or buttons,
text alternatives
Serve the same purpose as the non-text content. [I]

That wording is a slight modification of a proposal I made on 18 November (http://lists.w3.org/Archives/Public/w3c-wai-gl/2004OctDec/0385.html#start) and was approved during the Working Group's weekly conference call on 2 December 2004. It has not yet been incorporated into the current working drafts.

For more on this, see Gregg Vanderheiden's message of 20 November (http://lists.w3.org/Archives/Public/w3c-wai-gl/2004OctDec/0641.html#start)

Readers of this list may be interested to see that WCAG 2.0 provides separate success criteria for non-text content that is functional (such as graphical links and buttons) and for non-text content that conveys information.  For example, success criterion #2 reads as follows:
2. For all non-text content that is used to convey information,
text alternatives
convey the same information. [I]

In my personal view, there are cases (probably the majority) where alt text alone will be sufficient to meet this criterion (for example, when a graphical button displays an image of text, the alt text should match the graphical text).  In some cases, it will be necessary to provide both alt text and a longdesc (for example, the alt text for a chart showing traffic density could say alt="Traffic density Chart, June 2003" while the longdesc would point to a file describing the chart and presenting the same data in tabular form).

"Good design is accessible design." 
John Slatin, Ph.D.
Director, Accessibility Institute
University of Texas at Austin
FAC 248C
1 University Station G9600
Austin, TX 78712
ph 512-495-4288, f 512-495-4524
email jslatin@mail.utexas.edu
web http://www.utexas.edu/research/accessibility/


-----Original Message-----
From: w3c-wai-ig-request@w3.org [mailto:w3c-wai-ig-request@w3.org] On Behalf Of Tina Holmboe
Sent: Tuesday, December 21, 2004 7:33 am
To: w3c-wai-ig@w3.org
Subject: Re: Alt is not a description (was Re: when to use longdesc for images)

On 21 Dec, Matthew J. Giustino wrote:

> 2)The second example of that page;
> <A HREF="home.htm"><IMG SRC="home.gif" ALT="Link to the Home 
> page."></A>

> Which is a clear example of how "alt" is a description.

  It is a clear example of a common, and long-standing,
  misunderstanding. This:

    <A HREF="home.htm">
     <IMG SRC="home.gif" ALT="Link to the Home page."></A>

  says, in effect: "The link Link to the home page goes to home.htm"
  while a rewritten

    <A HREF="home.htm">
     <IMG SRC="home.gif" ALT="Home page."></A>

  gives the user the same information, without the repetition. The alt
  attribute is there to provide equivalent information in the case
  images cannot be loaded or seen.

  Consider it in this light: what exactly is the image meant to convey?
  Forgot for a moment exactly what it looks like; what information is it
  meant to give the user? Emotional response? (Cute puppy) Information?
  (A valid markup icon) Layout? ('shimmer' gif)

  Let's take a silly example.

    <img src="R9-4a.gif"
          alt="Image of a red circle with a red line over a hand">

  This is a descriptive alternative text of the US R9-4a street sign. If
  you want to tell someone what it -looks like-, then the above is
  great. If, however, you want to use it on your page to state that your
  chauffeurs do not pick up hitch-hikers, then it is wholly
  inappropriate and should be:

    <img src="R9-4a.gif"
          alt="Our chauffeurs do not pick up hitch-hikers!">

  That second example on the wcag page mean to convey that it is a link
  to the "homepage". It does this. Twice. It need a rewrite without

  I can warmly recommend Alan Flavell's excellent "Use of ALT texts in
  IMGs" (http://www.htmlhelp.com/feature/art3.htm) which is as close to
  final on the topic as we are likely to get.

 -    Tina Holmboe                    Greytower Technologies
   tina@greytower.net                http://www.greytower.net/
   [+46] 0708 557 905
Received on Tuesday, 21 December 2004 15:10:41 UTC

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