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Re: Time Bounds - Universal and User-Specific

From: Charles McCathieNevile <charles@w3.org>
Date: Tue, 20 Nov 2001 21:06:13 -0500 (EST)
To: Adam Victor Reed <areed2@calstatela.edu>
cc: <w3c-wai-gl@w3.org>
Message-ID: <Pine.LNX.4.30.0111202101060.11642-100000@tux.w3.org>
This question has been dealt with at length in the User Agent Guidelines
working group - it is their checkpoint 2.4

I have included here the full text of that checkpoint because I think it
specifies what we want (except we change "user agent" for "content":

2.4 Allow time-independent interaction. (P1)

1.	For rendered content where user input is only possible within a
finite time interval controlled by the user agent, allow configuration to
provide a view where user interaction is time-independent.
2.	The user agent may satisfy this checkpoint by pausing processing
automatically to allow for user input, and resuming processing on explicit
user request. When this technique is used, pause at the end of each time
interval where user input is possible. In the paused state:

 Alert the user that the rendered content has been paused (e.g., highlight
the "pause" button in a multimedia player's control panel).
 Highlight which enabled elements are time-sensitive.
 Allow the user to interact with the enabled elements.
 Allow the user to resume on explicit user request (e.g., by pressing the
"play" button in a multimedia player's control panel; see also checkpoint

3.	The user agent may satisfy this checkpoint by generating a
time-independent ("static") view, based on the original content, that offers
the user the same opportunities for interaction. The static view should
reflect the structure and flow of the original time-sensitive presentation;
orientation cues will help users understand the context for various
interaction opportunities.
4.	When satisfying this checkpoint for a real-time presentation, the
user agent may discard packets that continue to arrive after the construction
of the time-independent view (e.g., when paused or after the construction of
a static view).

Techniques for checkpoint 2.4

Note: If the user agent satisfies this checkpoint by pausing automatically,
it may be necessary to pause more than once when there are multiple
opportunities for time-sensitive user interaction When pausing, pause
synchronized content as well (whether rendered in the same or different
viewports) per checkpoint 2.6. In SMIL 1.0 [SMIL], for example, the "begin",
"end", and "dur" attributes synchronize presentation components. This
checkpoint does not apply when the user agent cannot recognize the time
interval in the presentation format, or when the user agent cannot control
the timing (e.g., because it is controlled by the server). See also
checkpoint 3.5, which involves client-driven content refresh.


Charles McCathieNevile    http://www.w3.org/People/Charles  phone: +61 409 134 136
W3C Web Accessibility Initiative     http://www.w3.org/WAI    fax: +1 617 258 5999
Location: 21 Mitchell street FOOTSCRAY Vic 3011, Australia
(or W3C INRIA, Route des Lucioles, BP 93, 06902 Sophia Antipolis Cedex, France)
Received on Tuesday, 20 November 2001 21:06:16 UTC

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