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LONGDESC: some current problems and a proposed solution added to the wiki

From: Peter Krantz <peter.krantz@gmail.com>
Date: Sat, 30 Jun 2007 12:22:31 +0200
Message-ID: <7b9ad66d0706300322m399d452ekf0b62d00ddad0c1c@mail.gmail.com>
To: public-html@w3.org


I agree with previous comments that there is a need to describe
complex images in a more structured way. The current method of using
longdesc to link to an extended description may not be the best way.

Problems with the current longdesc method:

- Assistive devices need to make an extra HTTP request to retrieve the
content. A risk for availability problems.
- It is unclear how the web page containing the extended description
should look. If it includes the web site navigation toolbars and
headers it increases the time to reach the content for the user.
- It is difficult to script usage of the extended content to e.g.
display it in a popup when hovering the image.
- Search engines need to make an extra request to get information
about the image.
- Forcing the user to navigate to a separate page increase the risk
for usability problems (do they know they can click the image?).


If research shows that longdesc usage is limited, now is a good time
to change the markup. Eric Eggert's suggestion makes sense but there
should be a connection with the image to enable programmatic discovery
and manipulation of the extended description text. As we should strive
for backwards compatibility I suggest the following.

    * longdesc attribute of the ig element is removed
    * the role attribute is used to identify a longdesc
    * the for attribute is used to connect the extended description to
a particular image

An example:

<img src="/flag.gif" id="ukflag" alt="">


<div role="longdesc" for="ukflag">
  <p>The Flag of Union has been the official flag of the United
Kingdom since the Act of Union of 1807, which created the modern
political entity known as the United Kingdom, which, this year,
celebrates its 200th anniversary.</p>

This method has the following advantages:

   1. Backwards compatible with HTML 4. Current UA:s will render the content.
   2. Easier for assistive devices to parse and present extended
description in a different context.
   3. Better usability. Extended description is available without the
need to navigate to a new page that may repeat navigation and header
   4. Scriptability/stylability. Extended content div can e.g. be
hidden and displayed on mouseover or whatever the designer wants.
   5. Easy to add this markup to existing web pages. An editor only
needs to wrap the existing description in a div like above to increase

This method has the following disadvantages:

   1. Makes pages with many complex images heavier to download.

Attacks/comments are welcome. Sorry of this method already has been
suggested by someone else.


Peter Krantz
Received on Saturday, 30 June 2007 10:22:36 UTC

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