- 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
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 14:47:38 UTC