Issue 30 Change Proposal: Include longdesc in HTML5
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
- 1 Issue 30 Change Proposal: Include longdesc in HTML5
- 1.1 Summary
- 1.2 Rationale
- 1.2.1 User and Authoring Requirements
- 1.2.2 Use Cases
- 1.2.3 Responses To Critiques of this Change Proposal
- 1.2.4 Comments to HTML Working Group in Support of longdesc
- 1.2.5 Objections, Responses, and Reviews
- 1.2.6 Relation to Issue 204 and ARIA describedby
- 1.2.7 Conclusion
- 1.3 Details
- 1.4 Impact
- 1.5 References
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
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:
- Describing a Logo
- Describing a Cartoon
- Describing Artwork
- Describing Screenshots
- Describing a Chart
- Describing a Photograph
- Describing an Email Banner
- Describing Illustrations
- Facilitating etext Image Descriptions
- Describing a Newspaper Image
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.
- Implementation Evidence
- Hidden Meta-Data
- Suggested Alternatives Are Not Viable Solutions
- Related Solutions Do Not Negate the Need for longdesc
- Recent Research on Usage
- 80/20 Rule
- Something for Everyone, Not Everything For Anyone
- Recent Research on Online Tutorials and Documentation
- Recent Research on Guidelines, Laws, Policy, and Standards
- Recent Research on Users
Comments to HTML Working Group in Support of longdesc
- Association of American Publishers (AAP), July 29, 2011
- Digital Image and Graphic Resources for Accessible Materials Center (DIAGRAM), February 25, 2011
- HTML-A11Y Task Force, May 16, 2011
Objections, Responses, and Reviews
- Objection to the Proposal: Keep the longdesc attribute for the img element deprecated By Laura Carlson
- Response to: ChangeProposals/DeprecateLongdesc By John Foliot (ARIA Section)
- Review of longdesc CPs By Charles Pritchard
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:
- Additions to HTML5's 4.8.1 img section are supplied at spec text for 4.8.1 The img element. Additions are indicated with <ZZZ></ZZZ>.
- Additions to HTML5's 10.6.1 section are supplied at spec text for 10.6.1 rendering section. Additions are indicated with <ZZZ></ZZZ> and include images and their longdesc files.
- The following should all mention that a longdesc may be used to provide a detailed description of the image, e.g. to help a person who cannot see to understand and appreciate image content from a description.
- 188.8.131.52.6 A graphical representation of some of the surrounding text should mention it as a way to make the association between an image and the relevant text explicit.
- 184.108.40.206.7 A purely decorative image that doesn't add any information should mention it as the preferred way to point to a description of the image if this is desired, rather than mis-using the alt attribute for this purpose.
- 220.127.116.11.10 A key part of the content should mention that where an image is a key part of the content, it should have sufficient text in the alt attribute to replace the image, and using the longdesc attribute for critical information is a mistake. However, it can be used for additional information if desired.
- Remove longdesc for img elements from the obsolete section of the spec.
- 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.