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[Issue 517] Proposal to address nested time containers.

From: Ian B. Jacobs <ij@w3.org>
Date: Tue, 03 Jul 2001 15:37:41 -0400
Message-ID: <3B421F05.A3C2D69D@w3.org>
To: w3c-wai-ua@w3.org

Based on discussions with Jon Ferraiolo and Dean Jackson at the 
28 June 2001 teleconference [1] about issue 517 [2], I'd like to
propose the following to address this question: What do checkpoints
4.4 and 4.5 mean in the case of nested time containers? The original
comment [3] from the SVG WG was:

    [Checkpoint 4.4] talks about controlling particular 
    animations on an individual basis. This is not practical 
    with SMIL and SVG as this goes against the basic data models
    in the languages. In SMIL and SVG (and QuickTime), there are time 
    containers which are masters over time-based content such as
    animations. The time container is the master that drives the
    as a slave. The animation just responds to commands such as "update 
    yourself to what you should look like X.Y seconds into the
    The only thing that is reasonable is to allow the ability to pause, 
    accelerate or decelerate the time containers. 

[Editor's note: So far the checkpoint does apply to the SMIL 2 model.
 The SVG WG comments continue]

   However, if you have nested time containers, things can still get
   complicated as the nested time containers themselves are just slaves
   their parent time containers. Selecting these nested time containers
   require extensive user interface work on the part of UA developers
   would represent  large amounts of work just to support this


   - A user agent must provide the required control for each of the
     content types listed (audio, animations).

   - Checkpoint 2.6 already requires that the UA respect synchronization
     cues, so if the user controls two pieces of synchronized content
(one parent,
     one child, for example), they should behave in a synchronized


   - Added to checkpoints 4.4 and 4.5 that when the time frame of one
     is controlled by the time frame of another element, this checkpoint
     requires control over the master. This is a sufficient technique
     not necessary, as independent control of "slaves" would also
satisfy the

   - A user agent may also provide independent control of the "slave"

   - Add a SMIL example of this to the Techniques document.
 1) Reference draft: 22 June 2001:

The SVG makes an additional comment:

   A SMIL or SVG UA has no way of determining whether an animation can
  recognized as purely stylistic. In fact, in presentation-oriented
  like SMIL and SVG, it is often unclear where content ends and styling 
  begins. It is meaningless to talk about UA not being required to
  the checkpoint for animations for purely stylistic effects as this is 
  almost never recognizable.

Response: That's fine and that means the style part of the checkpoint
not apply. But that doesn't require any change to UAAG 1.0.

 - Ian

[1] http://lists.w3.org/Archives/Public/w3c-wai-ua/2001JulSep/0002.html
[2] http://server.rehab.uiuc.edu/ua-issues/issues-linear-lc3.html#517
[3] http://lists.w3.org/Archives/Public/w3c-wai-ua/2001AprJun/0199
Ian Jacobs (ij@w3.org)   http://www.w3.org/People/Jacobs
Cell:                    +1 917 450-8783
Received on Tuesday, 3 July 2001 15:40:14 UTC

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