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Use Cases

The Chairs' initial August 11, 2010 decision stated, "A number of use cases for semantically rich, structured descriptions of images were provided, however those use cases are abstract and don't directly and specifically require the support of a longdesc attribute...Overall, the lack of identified use cases was found to be a strong objection."

Uses cases have been identified that directly and specifically require longdesc.

New Formal Use Cases Requiring longdesc

Recent research finds a number of distinct use cases covering the needs of authors, users, and organizations. These use cases all point to the longdesc attribute as being the most efficient and appropriate choice, and further the only choice to meet identified constraints and functional requirements. They also demonstrate how and why other proposed alternatives to longdesc fail on one or more constraints or functional requirements.

For formal use cases, please visit Long Description Research: Use Cases. They include:

  1. Describing a Logo
  2. Describing a Cartoon
  3. Describing Artwork
  4. Describing Screenshots
  5. Describing a Chart
  6. Describing a Photograph
  7. Describing an Email Banner
  8. Describing Illustrations
  9. Facilitating etext Image Descriptions
  10. Describing a Newspaper Image

For an explanation of use case elements including constraints and scenarios please consult the Use Case Key.

Primary Use Case Overview

Longdesc affords authors the native capability to provide information that is essential for blind and visually impaired users but would be redundant for sighted users and unacceptable to visual designers' aesthetics.

It is an accommodation mechanism for people who are blind or have a visual impairment and use a screen reader. It is a tool to supply programmatically determinable descriptions of images such as data visualization (i.e. charts and graphs), diagrams, cartoons, logos drawings, illustrations, maps, photographs, etcetera when:

  • An image's content is visually apparent and typically redundant to a sighted person, and/or
  • It is unacceptable to a marketing department or web author to use another technique due to aesthetic considerations. Many artists, designers, and marketers do not want their visual designs changed/ruined with visible link text. (Longdesc is natively free from a visual encumbrance.), and/or
  • The image also serves as a link. With longdesc it is programmatically possible to separate the activation of the longdesc for exposure from the UA's universal link activation action (which is usually activated with the ENTER key, the SpaceBar, or by mouse click), so that the linked image retains the expected behavior in response to user interaction while a discrete mechanism is used to retrieve the long description. , and/or
  • The description is external to the document.

On August 17, 2010 the cartoonist Kyle Weems (aka CSS Squirrel) explained web.archive:

@Nick - With the exception of this most recent comic, all the comics are made for sighted users and navigable via the previous/next links below the comic. Those links are targetable by the sort of technology a physically-disabled person would use to navigate most links.

The issue at hand was directed at a piece of technology made for non-sighted users, however, so this comic provided an exception to deal with that specific experience.

@Mattur - I have no qualms with other people using hyperlinks where they desire to provide alternate text. However, as a designer, I object to being told I must use those links myself. As you've pointed out on Twitter, the current design of the comic page would certainly support a hyperlink wrapping around the comic. However, my upcoming design already has functionality mapped to clicking the comic, and won't have space for a large "transcript here" hyperlink sitting around in plain sight (which would be distracting for the 99% of my users that are sighted). In that scenario, longdesc can and does serve my needs.

Also, are we going to pretend that using longdesc is difficult? Yes, people may use it wrong without some correction, but simply saying "Hey, put a URL there," is not complex at all, and most of longdesc's non-use is a lack of awareness or caring (most non-longdesc websites simply don't offer alt text at all.)"

Other Use Cases

The content in a longdesc's target explains what is visually evident. This is similar to an audio description of a video being redundant to people who can see. Audio descriptions describe items and/or actions that take place visually which are needed for complete understanding to people who can't see. Sighted users don't typically need them. The same is true of longdesc.

However, the following sighted people may be aided by access to a longdesc:

  • Users who have a cognitive or visual impairment.
  • Users who have small screens (e.g. mobile phone or screen magnifiers).
  • Users who turn off images to decrease bandwidth use in order to lower their Internet usage fees.
  • Authors, for ease of authoring and maintenance purposes.

Access to the content of the longdesc attribute for the sighted should be similar to television closed captions. Closed captions are encoded or invisible to the sighted by default and must be decoded or made visible. There is a reason that closed captions (as opposed to open captions) are the default on televisions. Sighted people rarely require them. To them, they are visual noise. Clutter. Redundant. But if a sighted person wants to enable closed captions (longdesc is not hidden meta-data) they can do so via a user preference built into the system menu. It is a user choice. Televisions do not have a default on-screen visual indicator. There is no forced visual encumbrance. This is by design.