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[HTML5] Verbose Descriptor Requirements (proposed bug/issue)

From: Gregory J. Rosmaita <oedipus@hicom.net>
Date: Thu, 16 Sep 2010 15:47:04 +0100
To: public-html-a11y@w3.org
Cc: wai-xtech@w3.org
Message-Id: <20100916144306.M94236@hicom.net>
TITLE: Verbose (As Long As Necessary) Descriptor Requirements

PROPOSED BUG: HTML5 Lacks a Verbose Descriptor mechanism

PROPOSED KEYWORDS: a11y,NotInW3CSpecYet

ISSUE:

HTML5 fails to adequately provide the functions that had been provided 
through the HTML 4 attribute longdesc [1]. Those functions are: 

   1. A direct, reusable programmatic mechanism to a long description 
      of an image without a forced visual encumbrance or default 
      visual indicator. 

   2. A method to reference a longer description of an image, without 
      including the content in the main flow of a page. 

Many images cannot be sufficiently described with other long description 
techniques. For instance, longdesc currently provides a solution for 
describing the content of images to the blind when it would be: 

  * Visually apparent and redundant to a sighted person. 

  * Unacceptable to the marketing department due to aesthetic 
    considerations. 

There is currently absolutely no other direct way of doing that without a 
longdesc.  This situation has been exacerbated by the HTML WG chairs' 
decision on HTML WG ISSUE-30 to remove longdesc from HTML5. [2] [3] [4]

PURPOSE

The purpose of a verbose descriptor is to describe an image. Such a 
description is essential for users who can not see, but who need access 
to information contained in a graphic. While verbose descriptors provide 
an important accommodation for the blind and visually impaired, a verbose 
descriptor can also be used by those with an extremely limited viewport 
or with cognitive difficulties as a guide to navigating and comprehending 
the described image. This means that the exposition of a verbose 
descriptor must not be an "either-or" proposition; rather, the user 
should be able to control the means of exposing the verbose descriptor, 
including the ability to simultaneously view the contents of the image 
and the contents of the verbose description. 


REQUIREMENTS

1. A programmatic mechanism to reference a specific set of structured 
   content, internal (enhanced describedby model) or external (HTML4 
   longdesc model) to the document containing the described image. 

2. A way to inform users and authors that a description is 
   present/available. 

3. A device independent way to access the descriptive content.

4. An explicit provision that accessing descriptive content, whether 
   internal or external to the document containing the image, does NOT 
   take the user away from the user's position in the document 
   containing the image where the verbose descriptor was invoked; 

5. A way to provide user control over exposition of the descriptor so 
   that rendering of the image and its description is not an either/or 
   proposition.

6. A method to reference a longer description of an image, without 
   including the content in the main flow of a page. 


SATISFYING THESE REQUIREMENTS FOR HTML5

OPTION 1: retain support for longdesc; allow for exposition of longdesc 
via user agent preference, context menu, or toggle inline as well as 
for simultaneous exposition of both the image and its description (useful 
for those with very limited viewports or users with cognitive issues, who 
may need a description's guide to assist in the user's understanding of 
the image being described); 

   * advantage 1.1: 2 major browsers already support longdesc natively 
     and are expected to continue to do so as part of their support 
     for HTML4x; 

   * advantage 1.2: authors are familiar with longdesc;

   * advantage 1.3. many public entities require longdesc for complex 
     images as part of their internal web content guidelines; note 
     that this includes technical materials on intranets, educational 
     materials, and governmental resources;

   * disadvantage 1.1: a valid longdesc value cannot currently consist
     of an IDREF -- authors need the flexibility to either point to a
     seperate document or to structured content appearing in the 
     same document


OPTION 2: add support for aria-describedby and deprecate longdesc in 
HTML5; 

   * drawback 2.1: aria-describedby is currently limited to text that 
     appears in the same document as the image being described; 

   * drawback 2.2: The content associated using aria-describedby as 
     currently implemented, is limited to unstructured text; 


OPTION 3: add support for external references and structured content to 
the aria-describedby attribute in HTML5 and deprecate longdesc; 


OPTION 4: Mint a describedby attribute for the img element (Bug 10455) [6]


REFERENCES:

[1] http://www.w3.org/TR/REC-html40/struct/objects.html#adef-longdesc-IMG

[2] http://www.w3.org/html/wg/tracker/issues/30

[3] HTML WG Issue-30 (longdesc) 
    http://www.w3.org/html/wg/tracker/issues/30

[4] Chairs' decision on HTML WG Issue-30 (longdesc) 
http://lists.w3.org/Archives/Public/public-html/2010Aug/att-0112/issue-30-
decision.html

[5] cover letter for Chairs' decision on HTML WG Issue 30 (longdesc) 
http://lists.w3.org/Archives/Public/public-html/2010Aug/0112.html

[6] http://www.w3.org/Bugs/Public/show_bug.cgi?id=10455


RESEARCH

* Longdesc Examples In the Wild 
http://www.d.umn.edu/~lcarlson/research/ld.html#wild

* Longdesc Guidelines, Laws, Policy, and Standards 
http://www.d.umn.edu/~lcarlson/research/ld.html#glps

* HTML 5 Issue: Image Equivalent Content (HTML WG Wiki page) 
http://www.w3.org/html/wg/wiki/LongdescRetention
Received on Thursday, 16 September 2010 14:47:33 UTC

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