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conditional versus optional content (thread from UA list)

From: gregory j. rosmaita <oedipus@hicom.net>
Date: Thu, 10 May 2001 17:50:36 -0400
Message-ID: <001701c0d99b$3f9c4ca0$5ab6f5d0@igor>
To: <w3c-wai-gl@w3.org>

the thread on the UA list on conditional versus optional content begins at:
the discussion that spawned the above-referenced thread appears in the
minutes of the 22 february 2001 UA telecon (under the heading "Discussion")

the UAAG definition of conditional content (from the 11 april 2001 working
group draft) follows:

   Conditional content
          Conditional content is content that, by specification, should
          be made available to users through the user interface,
          generally under certain conditions (e.g., user preferences or
          operating environment limitations). Some examples of
          conditional content mechanisms include:

          + The "alt" attribute of the IMG element in HTML 4. According
            to section 13.2 of the HTML 4 specification ([HTML4]): "User
            agents must render alternate text when they cannot support
            images, they cannot support a certain image type or when they
            are configured not to display images.

          + OBJECT elements in HTML 4. Section 13.3.1 of the HTML 4
            specification ([HTML4]) explains the conditional rendering
            rules of (nested) OBJECT elements.

          + The switch element and test attributes in SMIL 1.0. Sections
            4.3 and 4.4, respectively, of SMIL 1.0 [SMIL] explain the
            conditional rendering rules of these features.

          + SVG 1.0 [SVG] also includes a switch element and several
            attributes for conditional processing.

          + The NOSCRIPT and NOFRAMES elements in HTML 4 [HTML4] allow
            the author to provide content under conditions when the user
            agent does not support scripts or frames, or the user has
            turned off support for scripts or frames.

          Specifications vary in how completely they define how and when
          to render conditional content. For instance, the HTML 4
          specification includes the rendering conditions for the "alt"
          attribute, but not for the "title" attribute. The HTML 4
          specification does indicate that the "title" attribute should
          be available to users through the user interface ("Values of
          the title attribute may be rendered by user agents in a variety
          of ways...").

          Note: The Web Content Accessibility Guidelines 1.0 requires
          that authors provide text equivalents for non-text content.
          This is generally done by using the conditional content
          mechanisms of a markup language. Since conditional content may
          not be rendered by default, the current document requires the
          user agent to provide access to unrendered conditional content
          (checkpoint 2.3 and checkpoint 2.9) as it may have been
          provided to promote accessibility.
Received on Thursday, 10 May 2001 17:49:36 UTC

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