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[last call, S2] equivalent (to other content)

From: Al Gilman <asgilman@iamdigex.net>
Date: Mon, 13 Nov 2000 01:28:06 -0500
Message-Id: <Version.32.20001113003520.040bc7d0@pop.iamdigex.net>
Message-Id: <Version.32.20001113003520.040bc7d0@pop.iamdigex.net>
To: w3c-wai-ua@w3.org
The glossary entry "equivalent (for content)" employs a concept of an
"equivalency target" which is set apart from "the equivalents" for said
"equivalency target."

This distinction is incompatible with the common meaning of equivalency or

Equivalence relations are commonly reflexive and symmetrical.  Any thing by
itself forms an equivalence group.  If there are more than the one equivalent,
then there are alternatives and the situation becomes interesting.

In WCAG 1.1, in the glossary it says:

         Content is "equivalent" to other content when both fulfill
         essentially the same function or purpose upon presentation to
         the user. In the context of this document, the equivalent must
         fulfill essentially the same function for the person with a
         disability (at least insofar as is feasible, given the nature
         of the disability and the state of technology), as the primary
         content does for the person without any disability. For
         example, the text "The Full Moon" might convey the same
         information as an image of a full moon when presented to users.
         Note that equivalent information focuses on fulfilling the same
         function. If the image is part of a link and understanding the
         image is crucial to guessing the link target, an equivalent
         must also give users an idea of the link target. Providing
         equivalent information for inaccessible content is one of the
         primary ways authors can make their documents accessible to
         people with disabilities.
         As part of fulfilling the same function of content an
         equivalent may involve a description of that content (i.e.,
         what the content looks like or sounds like). For example, in
         order for users to understand the information conveyed by a
         complex chart, authors should describe the visual information
         in the chart.

The first sentence in this entry should be regarded as definitive.

The rest is explanatory.

It explains how this concept is _applied_ in the context of this document.  It
_does not_ further restrict the sense of the term itself, even as used in this

In no way did the WCAG mean to indicate that equivalence, as it relates to
accessibility in content, only applies when one user is a person with a
disability, or one of the alternative equivalents is incorporated for the
express purpose of making the ensemble accessible.  These are included in the
range of "equivalent alternatives" [or equivalently, "alternative equivalents]
but do not restrict these terms to those cases.

In the checkpoint which says:

   1.1 Provide a text equivalent for every non-text element

The term 'equivalent' is used solely to indicate how the text and non-text
alternatives are alike in the manner and to the extent stated in the first
sentence in the glossary, to wit:

         Content is "equivalent" to other content when both fulfill
         essentially the same function or purpose upon presentation to
         the user. 

The terms 'text' and 'non-text' are the part of this checkpoint which refer to
how the alternatives are different.  This information is independent of,
and in
addition to, the similarity indicated by the term 'equivalent.'

The UAAG should be re-worded to come closer to this understanding of the basic

The ATAG may provide useful examples of how to do this without being
unnecessarily abstract.

This principle is important to the current work of WAI-PF as regards the
of XHTML possibly on the basis of something derived from smil:switch as the
basis for marking all manner of equivalence groups.  

As PF work is affected by the outcome, and the basic question lies in an
interpretation of the WCAG concepts, it may be appropriate to coordinate with
WCA and PF to gain further input before attempting to resolve this comment.

Usage in headers.  Comments in response to the last call request for comments
have been classified S1, S2, or E based on the following rough scale:

S1: Substantive matter of the first (highest) criticality or importance to the
mission of the document.  The standard set is ineffective, the document is
contradictory, etc.

S2: Substantive matter of a somewhat lower criticality.  The document is hard
to comprehend, does not align well with related WAI documents, etc.

E: Editorial matters.  Not regarded as substantive.


User Agent Accessibility Guidelines 1.0

W3C Working Draft 23 October 2000

   This version:
Received on Monday, 13 November 2000 00:57:17 UTC

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