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Issue 30 Change Proposal: Include longdesc in HTML5

  • The following is a Change Proposal for HTML5 ISSUE-30 longdesc which has been reopened.
  • Editor: Laura Carlson, (laura.lee.carlson at gmail.com)
  • Date: January 31, 2011, last updated September 18, 2012


This change proposal describes the rationale for instating longdesc in HTML5, in order to provide accessibility support for web users who are blind, visually impaired, have learning disabilities, certain kinds of cognitive disabilities, or other disabilities where access to longer descriptions of complex images may be needed. It explains how longdesc provides an effective solution for content authors needing to provide longer descriptions of complex images while adhering to constraints, as well as how longdesc provides continuity with existing accessibility support for images that has been previously provided through HTML4 and XHTML1.

Specifically, this change proposal provides the following information, evidence for which is available in the linked pages below:

  • A summary of user and authoring requirements and use cases for longdesc
  • Evidence as to why longdesc is a better solution for meeting the requirements of web users with disabilities and web authors than other alternatives
  • A summary of responses to challenges to the evidence in this change proposal
  • A summary of problems with proposed alternatives such as ARIA describedby


User and Authoring Requirements

Documentation of requirements for a longer description mechanism in HTML include that such a mechanism afford user and author capabilities, some of which are highlighted here.

User Requirements Include

User-determined discoverability
The consumers of complex images will often require a discoverable programmatic mechanism to reference a longer description mechanism, either internal or external to the document containing the described.
No forced visual encumbrance
The user MUST be able to configure the longer description mechanism to be visible or not, according to their needs.
User choice of consuming
Upon discovery, a longer textual description MUST support user-initiated activation, and the user should be able to exit from the description at any point and return to the place in the main document where they left off.
User support of structured markup
The user MUST be able to utilize shortcut keys that rely on structure to perform functions.

Author Requirements Include

Support for structured markup
A longer textual description of a complex image MUST be capable of supporting structured mark-up (for example a pie-chart could be expressed as tabular data using actual <table> markup).
Portable & re-usable
The programmatic mechanism MUST provide a method to reference a longer description of an image, without including the content in the main flow of a page.
No forced visual encumbrance
By default the long description or long description indicator MUST not force a visual encumbrance or impact the visual user experience.
Any proposed mechanism MUST provide clear, direct, explicit, and strong long description semantics.
Ease of use
The longer description mechanism MUST be easy to author, easy to maintain and have authoring support in terms of tools and educational material to accommodate authors of differing skill sets.
Backwards compatible
Any proposed mechanism MUST include a means of accessing content added by authors using the HTML4 and XHTML1 attribute longdesc

Use Cases

Multiple and detailed use cases have been identified that directly and specifically require longdesc. The primary use case is that longdesc affords authors the native capability to provide information that is essential for people with disabilities while ahereing to constraints. For formal use cases consult Long Description Research: Use Cases. They include:

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

Other use cases have also been identified.

Responses To Critiques of this Change Proposal

Extensive evidence and responses have been gathered to clarify and explain the rationale for longdesc in response to critiques previously made, in particular to those in the Zero Edit Change Proposal. Please consult Rebuttals to Use Case Comments and the following for details.

Comments to HTML Working Group in Support of longdesc

Objections, Responses, and Reviews

Relation to Issue 204 and ARIA describedby

The HTML5 specification text for Issue 204: ARIA hidden, per instructions of the HTML Co-Chairs no longer encourages usage of ARIA describedby that could provide the impression that describedby could serve as a viable alternate longer description mechanism to longdesc. This change of the Issue 204 decision text in HTML5 follows a formal objection from the WAI Protocols and Formats Working Group (PFWG) noting implementation harm for assistive technologies that could result from using ARIA describedby in this manner.



Main Spec Changes:

Other Changes:


  • Makes longdesc more useful, robust, and encourages better user agent implementation.
  • Requires conformance checking to accept the attribute as valid, and would imply maintaining the existing requirement on Authoring Tools to allow the author to use this functionality. It would maintain conformance of HTML-4 tools and content, rather than the current expected change leaving them non-conforming.
  • Provides the benefits noted in the conclusion.