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Re: Conformance Level Clarification

From: Jason White <jasonw@ariel.its.unimelb.edu.au>
Date: Tue, 15 Feb 2005 13:18:33 +1100
Message-ID: <16913.23545.430210.333320@jdc.local>
To: "Chris Ridpath" <chris.ridpath@utoronto.ca>
Cc: "John M Slatin" <john_slatin@austin.utexas.edu>, "WAI WCAG List" <w3c-wai-gl@w3.org>

Chris Ridpath writes:
 > John wrote:
 > > We would say that the *delivery unit* conforms at
 > > level 1 if all level 1 success criteria are satisfied...
 > >
 > Yes, thanks for making this clear.

This is an accurate formulation, except that the term is "delivered
unit" not "delivery unit".
 > Loretta wrote:
 > > ...how would you envision level 1 conforming alt text
 > > differing from level 2 conforming alt text?
 > >
 > Level 1 alt text would only be required to meet the level 1 requirements
 > while level 2 alt text would be required to meet both level 1 and level 2
 > requirements.

The same as all other success criteria.
 > For example, level 1 alt text would be required to be present and describe
 > the image. Level 2 alt text would require more such as conforming to length
 > and avoiding placeholder values.

Some problems:

1. The guidelines don't refer to "alt text" if by that you mean the
   value of an XHTML ALT attribute. Consequently, you can't impose
   length constraints as these would be arbitrary, and would make it
   difficult or impossible to write alternatives for complicated

It might be argued that in dealing with complicated images, a short
label should be provided in the ALT attribute and full detail in a
document referred to by LONGDESC, but that's an HTML-specific
constraint that can't be expressed in the WCAG success criteria, which
have to apply across languages and formats. For example, how would you
apply it to the SVG DESC element?

Secondly, I would have thought that the definition of "text
alternative" would exclude place-holder values at level 1. A
place-holder value doesn't provide the same functionality or
information as the non-text content.

Thus, although it is in principle possible to add requirements to
level 2 concerning text alternatives, I am not persuaded that there is
a strong rationale for doing so.
Received on Tuesday, 15 February 2005 02:19:06 UTC

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