W3C home > Mailing lists > Public > w3c-wai-gl@w3.org > July to September 2001

Re: guideline 7.1 about screen flickering (fwd)

From: gregory j. rosmaita <oedipus@hicom.net>
Date: Thu, 26 Jul 2001 22:04:57 -0400
To: <w3c-wai-gl@w3.org>
Message-ID: <CEEMJDFDIKKPEJJLKBKJOEIMCAAA.oedipus@hicom.net>
KB: Most modern browsers can or should include this in configuration
options

GJR: which means that the answer is (all together now) the "until user
agents..." clause still applies until there are actually user agents that
conform to the following UAAG checkpoints (the text of which is drawn from
the 14 july 2001 working group working draft of UAAG 1.0 [reference 1]:

<quote>
      2.3 Render conditional content. (P1)

    1. Allow configuration to provide access to each piece of unrendered
       conditional content "C".
    2. The configuration may be a switch that, for all content, turns on
       or off the access mechanisms described in the next provision.
    3. When a specification does not explain how to provide access to
       this content, do so as follows:
          + If C is a summary, title, alternative, description, or
            expansion of another piece of content D, provide access
            through at least one of the following mechanisms:
               o (1a) render C in place of D;
               o (2a) render C in addition to D;
               o (3a) provide access to C by querying D. In this case,
                 the user agent must also alert the user, on a
                 per-element basis, to the existence of C (so that the
                 user knows to query D);
               o (4a) allow the user to follow a link to C from the
                 context of D.
          + Otherwise, provide access to C through at least one of the
            following mechanisms:
               o (1b) render a placeholder for C, and allow the user to
                 view the original author-supplied content associated
                 with each placeholder;
               o (2b) provide access to C by query (e.g., allow the user
                 to query an element for its attributes). In this case,
                 the user agent must also alert the user, on a
                 per-element basis, to the existence of C;
               o (3b) allow the user to follow a link in context to C.
    4. To satisfy this checkpoint, the user agent may provide access on a
       per-element basis (e.g., by allowing the user to query individual
       elements) or for all elements (e.g., by offering a configuration
       to render conditional content all the time).

   For all content

   Note: For instance, an HTML user agent might allow users to query each
   element for access to conditional content supplied for the "alt",
   "title", and "longdesc" attributes. Or, the user agent might allow
   configuration so that the value of the "alt" attribute is rendered in
   place of all IMG elements (while other conditional content might be
   made available through another mechanism). See checkpoint 2.10 for
   additional placeholder requirements.

     2.4 Allow time-independent interaction. (P1) [note: the wording of
     this checkpoint will change in the next draft - consult the minute's
     of the 26 july 2001 UA WG telecon, archived at:
<http://lists.w3.org/Archives/Public/w3c-wai-ua/2001JulSep/0155>
     for more details of the discussion of this checkpoint -- GJR]

    1. For content where user input is only possible within a finite time
       interval controlled by the user agent, allow configuration to make
       the time interval "infinite". Do this by pausing automatically at
       the end of each time interval where user input is possible, and
       resuming automatically after the user has explicitly completed
       input.
    2. In this configuration, alert the user when the session has been
       paused and which enabled elements are time-sensitive.
    3. When the user pauses a real-time presentation, the user agent may
       discard packets that continue to arrive during the pause.

   For all rendered content

   Note: In this configuration, the user agent may have to pause the
   presentation more than once if there is more than one opportunity for
   time-sensitive input. 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. The user may
   explicitly complete input in many different ways (e.g., by following a
   link that replaces the current time-sensitive resource with a
   different resource). 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.

      2.7 Repair missing content. (P2)

    1. Allow configuration to generate repair text when the user agent
       recognizes that the author has failed to provide conditional
       content that was required by the format specification.
    2. The user agent may satisfy this checkpoint by basing the repair
       text on any of the following available sources of information: URI
       reference, content type, or element type.

   For all content

   Note: Some markup languages (such as HTML 4 [HTML4] and SMIL 1.0
   [SMIL] require the author to provide conditional content for some
   elements (e.g., the "alt" attribute on the IMG element). Repair text
   based on URI reference, content type, or element type is sufficient to
   satisfy the checkpoint, but may not result in the most effective
   repair. Information that may be recognized as relevant to repair might
   not be "near" the missing conditional content in the document object.
   For instance, instead of generating repair text on a simple URI
   reference, the user agent might look for helpful information near a
   different instance of the URI reference in the same document object,
   or might retrieve useful information (e.g., a title) from the resource
   designed by the URI reference.

      2.9 Render conditional content automatically. (P3)

    1. Allow configuration to render all conditional content
       automatically. The user agent is not required to render all
       conditional content at the same time in a single viewport.
    2. Provide access to this content according to format specifications
       or where unspecified, by applying one of the following techniques
       described in checkpoint 2.3: 1a, 2a, or 1b.

   For all content

   Note: For instance, an HTML user agent might allow configuration so
   that the value of the "alt" attribute is rendered in place of all IMG
   elements (while other conditional content might be made available
   through another mechanism). The user agent may offer multiple
   configurations (e.g., a first configuration to render one type of
   conditional content automatically, a second to render another type,
   etc.).

      2.10 Toggle placeholders. (P3)

    1. Once the user has viewed the original author-supplied content
       associated with a placeholder, allow the user to turn off the
       rendering of the author-supplied content.

   For all rendered content

   Note: For example, if the user agent substitutes the author-supplied
   content for the placeholder in context, allow the user to "toggle"
   between placeholder and the associated content. Or, if the user agent
   renders the author-supplied content in a separate viewport, allow the
   user to close that viewport. Note: See checkpoint 2.3, provision (1b)
   for placeholder requirements.

    3.1 Toggle background images. (P1)

    1. Allow configuration not to render background images.
    2. In this configuration, the user agent is not required to retrieve
       background images from the Web.
    3. This checkpoint only requires control of background images for
       "two-layered renderings", i.e., one rendered background image with
       all other content rendered "above it".

   For all content
   Content type labels: Image.

   Note: See checkpoint 2.3 for information about how to provide access
   to unrendered background images. When background images are not
   rendered, user agents should render a solid background color instead
   (see checkpoint 4.3).

        3.2 Toggle audio, video, animated images. (P1)

    1. Allow configuration not to render audio, video, or animated images
       except on explicit user request. This configuration is required
       for content rendered without any user interaction (including
       content rendered on load or as the result of a script), as well as
       content rendered as the result of user interaction (e.g., when the
       user activates a link).
    2. The user agent may satisfy this checkpoint by making video and
       animated images invisible and audio silent, but this technique is
       not recommended.
    3. When configured not to render content except on explicit user
       request, the user agent is not required to retrieve the audio,
       video, or animated image from the Web until requested by the user.

   For all content
   Content type labels: Animation, Video, Audio.

   Note: See checkpoint 2.3 for information about how to provide access
   to unrendered audio, video, and animated images. See also checkpoint
   4.5, checkpoint 4.9, and checkpoint 4.10.

     3.3 Toggle animated/blinking text. (P1)

    1. Allow configuration to render animated or blinking text as
       motionless, unblinking text. Blinking text is text whose visual
       rendering alternates between visible and invisible, any rate of
       change.
    2. In this configuration, the user must still have access to the same
       text content, but the user agent may render it in a separate
       viewport (e.g., for large amounts of streaming text).
    3. The user agent also satisfies this checkpoint by always rendering
       animated or blinking text as motionless, unblinking text.

   For all content
   Content type labels: VisualText.

   Note: Animation (a rendering effect) is different from streaming (a
   delivery mechanism). Streaming content might be rendered as an
   animation (e.g., an animated stock ticker) or as static text (e.g.,
   movie subtitles, which are rendered for a limited time, but do not
   give the impression of movement). See also checkpoint 3.5. apply for
   blinking and animation effects that are caused by mechanisms that the
   user agent cannot recognize.

     4.4 Slow multimedia. (P1)

    1. Allow the user to slow the presentation rate of audio and
       animations (including video and animated images).
    2. For a visual track, provide at least one setting between 40% and
       60% of the original speed.
    3. For a prerecorded audio track including audio-only presentations,
       provide at least one setting between 75% and 80% of the original
       speed.
    4. When the user agent allows the user to slow the visual track of a
       synchronized multimedia presentation to between 100% and 80% of
       its original speed, synchronize the visual and audio tracks. Below
       80%, the user agent is not required to render the audio track.
    5. The user agent is not required to satisfy this checkpoint for
       audio and animations whose recognized role is to create a purely
       stylistic effect.

   For all rendered content
   Content type labels: Animation, Audio.

   Note: Purely stylistic effects include background sounds, decorative
   animated images, and effects caused by style sheets. The style
   exception of this checkpoint is based on the assumption that authors
   have satisfied the requirements of the "Web Content Accessibility
   Guidelines 1.0" [WCAG10] not to convey information through style alone
   (e.g., through color alone or style sheets alone). See checkpoint 2.6
   and checkpoint 4.7.

     4.5 Start, stop, pause, advance multimedia. (P1)

    1. Allow the user to stop, pause, resume, fast advance, and fast
       reverse audio and animations (including video and animated images)
       that last three or more seconds at their default playback rate.
    2. The user agent is not required to satisfy this checkpoint for
       audio and animations whose recognized role is to create a purely
       stylistic effect.
    3. The user agent is not required to play synchronized audio during
       fast advance or reverse of animations (though doing so may help
       orient the user).
    4. The user agent is not required to play animations during fast
       advance and fast reverse.
    5. When the user pauses a real-time audio or animation, the user
       agent may discard packets that continue to arrive during the
       pause.

   For all rendered content
   Content type labels: Animation, Audio.

   Note: See checkpoint 4.4 for more information about the exception for
   purely stylistic effects. This checkpoint applies to content that is
   either rendered automatically or on request from the user. Respect
   synchronization cues per checkpoint 2.6.

   4.7 Slow other multimedia. (P2)

    1. Allow the user to slow the presentation rate of audio and
       animations (including video and animated images) not covered by
       checkpoint 4.4.
    2. The same speed percentage requirements of checkpoint 4.4 apply.

   For all rendered content
   Content type labels: Animation, Audio.

   Note: User agents automatically satisfy this checkpoint if they
   satisfy checkpoint 4.4 for all audio and animations.

     4.8 Control other multimedia. (P2)

    1. Allow the user to stop, pause, resume, fast advance, and fast
       reverse audio and animations (including video and animated images)
       not covered by checkpoint 4.5.

   For all rendered content
   Content type labels: Animation, Audio.

   Note: User agents automatically satisfy this checkpoint if they
   satisfy checkpoint 4.5 for all audio and animations.

      11.5 Default binding requirements. (P2)

    1. Ensure that the user agent default input configuration includes
       bindings for the following functionalities required by other
       checkpoints in this document:
          + move focus to next enabled element, and move focus to
            previous enabled element;
          + activate focused link;
          + search for text;
          + search again for same text;
          + increase size of rendered text, and decrease size of rendered
            text;
          + increase global volume, and decrease global volume;
          + stop, pause, resume, fast advance, and fast reverse selected
            audio and animations (including video and animated images).
    2. If the user agent supports the following functionalities, the
       default input configuration must also include bindings for them:
          + next history state (forward), and previous history state
            (back);
          + enter URI for new resource;
          + add to favorites (i.e., bookmarked resources);
          + view favorites;
          + stop loading resource;
          + reload resource;
          + refresh rendering;
          + forward one viewport, and back one viewport;
          + next line, and previous line.

   For user agent features

   Note: This checkpoint does not make any requirements about the ease of
   use of default input configurations, though clearly the default
   configuration should include single-key bindings and allow easy
   operation. Ease of use is ensured by the configuration requirements of
   checkpoint 11.3.
</quote1>

oh, and just so that it is clear what precisely the User Agent Accessibility
Guidelines (UAAG) 1.0 consider "animation", here is the definition provided
by the 14 July 2001 draft of that document:

<quote2>
   Animation
          In this document, an "animation" refers to content that, when
          rendered, creates a visual movement effect automatically (i.e.,
          without manual user interaction). This definition of animation
          includes video and animated images. Animation techniques
          include:
          + graphically displaying a sequence of snapshots within the
            same region (e.g., as is done for video and animated images).
            The series of snapshots may be provided by a single resource
            (e.g., an animated GIF image) or from distinct resources
            (e.g., a series of images downloaded continuously by the user
            agent).
          + scrolling text (e.g., achieved through markup or style
            sheets).
          + displacing graphical objects around the viewport (e.g., a
            picture of a ball that is moved around the viewport giving
            the impression that it is bouncing off of the viewport
            edges). For instance, the SMIL 2.0 [SMIL20] animation modules
            explain how to create such animation effects in a declarative
            manner (i.e., not by composition of successive snapshots).
</quote2>

References:
1. 14 July 2001 Working Group Draft of the User Agent Accessibilty
Guidelines 1.0
URI: http://www.w3.org/WAI/UA/WD-UAAG10-20010714/
Received on Thursday, 26 July 2001 22:04:02 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Monday, 7 December 2009 10:47:11 GMT