A Report of the WAI-CG Task Force on Alternative Text
Task Force Facilitator: Janina Sajka, PFWG Chair
Date: 10 June 2009
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.
altis a very important accessibility attribute (it is supported by all browsers, most authoring tools and is the most well known accessibility technique among authors).
alt"required" in HTML 4.01 raised public awareness of Web accessibility in general.
altbut in general cannot certify the correctness of the text string.
altattribute as one of the valid mechanisms to provide short text alternatives.
aria-labelledbyas a second valid mechanism for short text alternatives.
NOTE: These recommendations assume that ARIA features referenced in this document are included in HTML 5.
<img>is only valid when at least one of the following is true:
altis present (empty or non-empty) OR
aria-labelledbyis present (non-empty only) OR
<img>is located within a
<figure>that has a non-empty
role="presentation" be taken from ARIA 1.0
<img>without a @
roleattribute is assumed to be the equivalent of <IMG @
role="img"> (and would follow the rules in #1 above)
NOTE: 'Presentation' should not be defined to be broader than what is defined by ARIA
alt="" (also see (4))
INTENT: That it is VALID to use either ROLE and/or ALT="" to mark "presentational" content.
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.
<legend>) should be capable of handling structured content. Our primary concern is that short text alternatives be able to support inline text structure, such as abbreviations, language changes, emphasis, etc.
RATIONALE: It would be helpful for the short alternative text mechanism to support structured text.
NOTE: Long text alternatives go beyond short text alternatives and allow users (at their request) to get detailed information about non-text content.
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.
RATIONALE: Current LONGDESC can support structured content. This should not be lost with any new mechanisms.
aria-describedbywill be supported by assistive technologies at least as well as longdesc when HTML5 becomes a W3C Recommendation:
aria-describedbyis incorporated in HTML5
aria-describedbyallows pointing to long text alternatives that are off of the page (by pointing to a link on the page)
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 is not widely used by authors at this time. (NOTE: it is understood that aria-describedby cannot point off page directly.)
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.
We believe some sample authoring workflows will be helpful. Two are provided here.