WAI CG Consensus Resolutions on Text alternatives in HTML 5

A Report of the WAI-CG Task Force on Alternative Text
Task Force Facilitator: Janina Sajka, PFWG Chair
Date: 10 June 2009

About This Task Force

This report provides WAI consensus recommendations for alternative text support in HTML 5. On January 14, 2009 the WAI-CG created a Task Force on Alternative Text, to consider the various alternative text approaches discussed over the past few years, and to develop consensus WAI recommendations for appropriate handling of alternative text in HTML5. These recommendations have been reviewed by the following WAI Working Groups: Authoring Tools Working Group (AUWG), Protocols & Formats Working Group (PFWG), User Agent Working Group (UAWG), and Web Content (WCAG WG).

NOTE: Suggestions for use of elements, attributes, and attribute values are provided in context of those features we currently understand HTML to provide.


The following background information is provided to help in understanding the specific recommendations below. It can also serve as context and guiding principles should markup solutions that differ from those recommended below be considered.


Principles underlying the advice below

  1. The working group recommends that HTML5 provide mechanisms for both short and long text alternatives.
  2. A short text alternative (using one of the mechanisms) should be required for validity but the long description should not be required.
  3. We recommend continued inclusion of the alt attribute as one of the valid mechanisms to provide shorttext alternatives.
  4. We recommend aria-labelledby as a second valid mechanism for short text alternatives.
  5. We recommend

Specific recommendations regarding Short Text Alternatives

NOTE: These recommendations assume that ARIA features referenced in this document are included in HTML 5.

  1. <img> is only valid when at least one of the following is true:
    NOTE: The intent here is twofold.
    1. to allow different methods to be used for providing short text alternatives (e.g. ALT or LABELLEDBY or LEGEND)
    2. to note that short text alternatives are not needed for content that is "presentational" as defined by ARIA
  2. That

    NOTE: 'Presentation' should not be defined to be broader than what is defined by ARIA

  3. For cases in which it is appropriate for user agents to ignore the presence of an image (e.g. when the image is used for decoration, for formatting, or when the image is invisible), one or both of the following may be used:

    INTENT: That it is VALID to use either ROLE and/or ALT="" to mark "presentational" content.

  4. alt="" WITHOUT an accompanying role="presentation" triggers a non-critical validator warning recommending use of role="presentation" (but @alt="" remains technically valid)

    INTENT: To encourage the use of role=presentation - by encouraging (but not requiring) its use even when alt="" is used.

  5. We suggest new mechanisms for short text alternatives (e.g. aria-labelledby, <legend>) should be capable of handling structured content. Our primary concern is that short text alternatives be able to supportinline text structure, such as abbreviations, language changes, emphasis, etc.

    RATIONALE: It would be helpful for the short alternative text mechanism to support structured text.

Recommendations regarding Long Text Alternatives

NOTE: Long text alternatives go beyond short text alternatives and allow users (at their request) to get detailed information about non-text content.

  1. Long text alternatives (e.g. aria-describedby ) should not be required for validity (though they may be required by WCAG 2.0 for some types of non-text content).

    RATIONALE: A long text alternative is not always required for accessibility. A short text alternative is often sufficient. So a long text alternative should not be required for validity.

  2. Mechanisms for long text alternatives should be capable of handling structured content.

    RATIONALE: Current LONGDESC can support structured content. This should not belost with any new mechanisms.

  3. Because we are confident that aria-describedby will be supported by assistive technologies at least as well as longdesc when HTML5 becomes a W3C Recommendation:

    RATIONALE: It is important that a long text mechanism exist which is capable of pointing off page. Long descriptions are often too lengthy and detailed to be included on the main page. If aria-describedby can point off page (by pointing to a link on the page) then it would remove any need for continued support of LONGDESC which isnot widely used by authors at this time. (NOTE: it is understood that aria-describedby cannot point off page directly.)

Recommendations regarding auto-generated alternative text

We have reached the following consensus concerning "automatically generated" alternative text:
In order to address both the validity and human generation concerns, we do not oppose the creation of 'autogenerated' and 'missing' attributes where either one of these could be used to make an image that does not have any human-generated text alternatives valid. (Note: It is important that this marker is not included in the alternative text string itself.)"

Please refer to Use Case #2 below.

ADDENDUM - Use Cases

We believe some sample authoring workflows will be helpful. Two are provided here.

Use Case 1 (author for whom "alt" is the paramount accessiblity feature)

  1. creates a web page with images
  2. @alt given value when user remembers
  3. in a few cases, the user wants the images to be ignored so he uses alt=""
  4. an accessibility check or validity check before publishing reveals a few missed @alts, the user returns and fixes them
  5. the validity checker suggests the use of role="presentation" in addition to alt="".
  6. the user takes the advice and adds the role="presentation"

Use Case 2 (author using a photo sharing site)

  1. author logs into the photo sharing site
  2. author uses the uploader feature to upload 50 pics of a vacation (XYZ0001.png, XYZ0002.png,..., XYZ0050.png) into an album the author calls "Paris 2009".
  3. a prompt appears asking the author to write descriptive labels for each image to facilitate text searching and access by people with disabilities.
  4. the author logs off without adding individual text alternatives.
  5. the photo sharing site assigns the @alt strings "Photo 1 of 50 of album Paris 2009"
  6. 6. when the author logs back in they still see indicators on the images and/or the album that reminds them that theimages are still lacking descriptive labels.