There is too great a leap, here. One either has to both present the same information and fulfil the same purpose or one only has to provide a nominative description of the purpose in text.
There is an important middle ground.
Proposed Change:
Make it more like the priorities in WCAG1:
The strongest requirement is that the text alternative accomplish the purpose of the non-text content it is an alternative for. The desired way to do this is to present the same information, but that lower-level agreement betweeen the alternatives is at a lower level of criticality.
Even this is not the right requirement because there needs to be recognition that the content can succeed by affording equivalent facilitation i.e. a go-path that succeeds for this user at a higher level of aggregation.
Thank you for your comment. We have modified 1.1.1 as follows:
1.1.1 Non-text Content: Except for the situations listed below, a text alternative that presents equivalent information is provided for all non-text content.
* Controls-Input: If non-text content is a control or accepts user input, then it has a name that describes its purpose. (See also Guideline 4.1 Support compatibility with current and future user agents, including assistive technologies)
* Media-Test-Sensory: If non-text content is multimedia , live audio-only or live video-only content, a test or exercise that must be presented in non-text format , or primarily intended to create a specific sensory experience , then text alternatives at least identify the non-text content with a descriptive text label. (For multimedia, see also Guideline 1.2 Provide synchronized alternatives for multimedia.)
* CAPTCHA: If the purpose of non-text content is to confirm that content is being accessed by a person rather than a computer, then text alternatives that identify and describe the purpose of the non-text content are provided and alternative forms in different modalities are provided to accommodate different disabilities.
* Decoration-Formatting-Invisible: If non-text content is pure decoration, or used only for visual formatting, or if it is not presented to users, then it is implemented such that it can be ignored by assistive technology.
Developed and maintained by Jon Hardin at the Trace Center, University of Wisconsin-Madison.
$Date: 2007/05/17 13:52:57 $ $Author: bcaldwel $