control of presentation for conditional content, in particular backgrounds [was: Re: Notes from W3C User Agent Teleconference for 13 July 2006]

Regarding your discussion of "Toggle background images (P1)"

You went back and forth about whether this is a UA or a content
requirement.  Also whether 3.1 applies to whole-page or page-part
backgrounds.  I would take the position that it applies to backgrounds
of page parts as well as to whole pages.  The toggle control could
affect all backgrounds identifiable as such in the page, though.  Or
it could be scoped to a current object.

As far as player vs. content requirements, there are some of each.

This relates to my comment to WCAG 2.0 in the area of
"Distinguish two interfaces"

http://lists.w3.org/Archives/Public/public-comments-wcag20/2006Jun/att-0192/WCAG2comment-AG-2interfaces.html 


The point is that if the function of the image is as an expendable
background, and replacing the background with a uniform background of
a suitably contrasting color will enhance the perceptibility of the
foreground, information-bearing shapes, then the user needs to be
able to suppress the rendering of the background.

This applies whether the author's suggested presentation has one
background for the whole page or for some sub-element in the page.

That is the requirement at the user interface, that the user can
suppress backgrounds; where a background is something inessential
which has the potential to interfere with processing the foreground,
and the foreground is sufficient to convey the essential core of the
information.

Deeper down, there are allocated requirements to the format, the
browser, and the author.

The format has to provide ways to separate the data that communicates
the foreground from the data that communicates the background, and to
identify which is which.

The player has to afford the user the capability to choose whether to
display the background with the foreground or the foreground alone,
without the background.

And the author has to respect the semantic distinction between
background and foreground. That is to say, the information that is
being communicated to the user needs to be complete as represented in
the foreground data, or the 'background' format is being abused. If
you cannot recognize the right information from the display of the
foreground alone, then the thing communicated in the background
syntax is not a semantic background and the author's responsibility
has not been fulfilled.

This goes for audio and visual content alike.

That's a quick dump as I understand how it should work.

The format should include support for backgrounds but define
these as conditional content.  The UA should implement user
control over the rendering decision for such conditional content.

The author should a) use the background feature in the format
to enable user control of rendering, and b) make sure that the
conditional content is indeed inessential, that the presentation
works with the background suppressed.

Al

Received on Thursday, 13 July 2006 21:17:48 UTC