W3C home > Mailing lists > Public > w3c-wai-ua@w3.org > January to March 2001

[Action] Proposal to clarify checkpoint 2.9

From: Ian Jacobs <ij@w3.org>
Date: Sat, 17 Mar 2001 17:06:52 -0500
Message-ID: <3AB3DFFC.C432E37F@w3.org>
To: w3c-wai-ua@w3.org

At the 15 March 2001 teleconference [1], I received an action
item to clarify the meaning of checkpoint 2.9 in the 9 March 2001
draft [2]. The checkpoint reads:

  "2.9 Allow configuration to create the conditions under which
  conditional content is rendered.  [Priority 3]"

To understand the intention of this checkpoint, here's an example
from the HTML 4.01 specification: when to render "alt" for the
IMG element. The HTML 4.01 specification states:

  "The alt attribute specifies alternate text that is rendered
  when the image cannot be displayed (see below for information
  on how to specify alternate text ). 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."

In this case, there are three conditions under which a conforming
user agent must render alt instead of the image:

 1) Images not supported
 2) Image type not supported
 3) Configured not to display images

I think our intention was not really to simulate one or more of
these conditions (why simulate lack of support for a particular
image type?), but rather to achieve the result of any one of
these conditions: that alt be rendered instead of IMG.

While checkpoint 2.3 is about element-level rendering control, I
think that checkpoint 2.9 is about global configuration so that
content that would only be rendered automatically under certain
conditions (per checkpoint 2.1) is rendered automatically,
whatever the current conditions.

Specs may not say much about when or how to render
conditional content.

 a) The specification might say nothing about rendering conditions
    (the case for "title" or "longdesc" in HTML, for example).

 b) The specification might define rendering conditions, but not
    how to render (one could argue that "alt" falls into this 

 c) The specification might define both the rendering conditions
    and how to render (I think OBJECT in HTML falls into this case,
    and probably SMIL test attributes do as well).

Checkpoint 2.3 takes all three into account. It may therefore be
helpful to define 2.9 in terms of 2.3.


  "2.9 Allow configuration so that the conditional content
  rendering mechanisms used to satisfy checkpoint 2.3 are applied
  automatically. [Priority 3]"

     Note: For example, suppose an HTML user agent satisfies
     checkpoint 2.3 by allowing the user to replace each IMG
     element individually with its associated "alt" attribute. As
     part of satisfying the current checkpoint, the user agent
     might allow configuration to render no IMG elements and
     instead to render their associated "alt" attributes.

  Furthermore, we can clarify 2.3 by adding examples to
  the Note (which we used to have, in fact), as in:

     Note: This checkpoint requires "element level" user control
     of rendering. For instance, an HTML user agent might satisfy
     this checkpoint by allowing the user to select each IMG
     element and to replace it on demand with the text of its
     "alt" attribute. Or, the user agent might render the "alt"
     text in addition to the element. Or the user agent might
     allow the user to query the element for both the "alt" and
     "longdesc" values (and to allow the user to retrieve the
     longdesc" resource). The configuration requirement of this
     checkpoint is global: the user agent is only required to
     provide one switch that turns on or off these element-level
     rendering mechanisms.

 - Ian

[1] http://lists.w3.org/Archives/Public/w3c-wai-ua/2001JanMar/0427
[2] http://www.w3.org/WAI/UA/WD-UAAG10-20010309/

Ian Jacobs (jacobs@w3.org)   http://www.w3.org/People/Jacobs
Tel:                         +1 831 457-2842
Cell:                        +1 917 450-8783
Received on Saturday, 17 March 2001 17:06:55 UTC

This archive was generated by hypermail 2.4.0 : Friday, 17 January 2020 20:38:30 UTC