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Re: User Agent Accessibility Guidelines comments: font-size UI

From: Ian Jacobs <ij@w3.org>
Date: Mon, 22 Nov 1999 12:40:15 -0500
Message-ID: <38397FFF.F77F40A2@w3.org>
To: Todd Fahrner <fahrner@pobox.com>
CC: w3c-wai-ua@w3.org
Todd Fahrner wrote:
> I sent the stuff below to the wrong address. I expect some of you saw
> it anyway. Just to be sure, I send again.
>   --
> This document: http://www.w3.org/TR/1999/WD-WAI-USERAGENT-19991105/
> Contains these bits:
> http://www.w3.org/TR/1999/WD-WAI-USERAGENT-19991105/#gl-user-control-styles
> http://www.w3.org/TR/WAI-USERAGENT-TECHS/#tech-control-text-size
> ...which are less than usefully explicit for "priority 1" items, and
> unfortunate implementation precedent proves that elaboration is
> needed.

Do you mean that the URIs are not explicit enough or the techniques?
Assuming you mean the techniques...
> Currently, the only techniques cited to assure user control of font size are
> "...[A]llow the user to control font size through style sheets or the
> user interface. Or allow the user to magnify text." and "Implement
> the CSS 'font-size' property."
> I can think of at least one implementation [WinIE5] which arguably
> passes muster under such lax language, which nevertheless presents
> serious usability problems in this area. The result is that many
> authors are less ready to embrace accessibility-conscious visual
> design techniques.
> The problem lies in the details of the CSS font-size property
> implementation, for which no explicit normative references exist. The
> CSS Recommendations, for their part, have tended to avoid UI
> specifics that might offend some members' sense of "turf", as it can
> affect competitive issues such as look-and-feel, OS integration,
> etc., or so it seems to me. This W3C product, however, seems like the
> right vehicle.
> For the sake of "getting to the point", I'll suggest
> additions/revisions first, with discussion of rationale to follow:
> *  Implement the CSS 'font-size' property as follows:
>     *  When a single font-size value is solicited in UI, the font-
>        size choice must define the value of the 'medium' font-size
>        keyword. Larger and smaller absolute size keyword values must be
>        computed relative to the user-chosen 'medium' value.
>     *  To avoid confusion, circularity, and indeterminacy, user-chosen
>        font-size values should not themselves be given in keyword
>        terms (e.g. 'medium', 'smaller', etc.), but in length units
>        appropriate to the media type (e.g., 16px for the screen media
>        type, 12pt for print, etc.).
>     *  UAs should take available resolution into account when
>        calculating the CSS absolute font-size keyword intervals, such
>        that, e.g., the three size values below 'medium' remain legible
>        and distinct from one another as long as the user-chosen 'medium'
>        value is itself at least three steps above the legibility floor,
>        as determined by device and font design constraints.[1]
>     *  the font-size choice exposed to the user in UI must provide a
>        font-size value for the root elements of documents to be rendered.

Are these recommendations appropriate for the UAGL? They seem to
be more appropriate closer to CSS (e.g., in a W3C Note). The UAGL
could then refer to them. I hate to hide important CSS ideas in
the UAGL Techniques Document.
> *  Implement the CSS2 Processing Model
>     (http://www.w3.org/TR/1998/REC-CSS2-19980512/intro.html#processing-model)
>     such that a font-size specified on the document root (e.g., HTML)
>     will inherit predictably per the CSS cascading and inheritance rules
>     (http://www.w3.org/TR/1998/REC-CSS2-19980512/cascade.html) to all
>     children, including HTML TABLE elements.

The CSS2 Processing Model is not normative. The CSS cascade is and
should be implemented.
> The reason for most of these elaborations should be clear upon
> considering their *lack* in practice. If an author wishes to respect
> the font size needs of the user, s/he must be able to assume certain
> sympathetic correlations between hir stylesheet rules and those of
> the user, as well as predictable cascading and inheritance rules.
> This is common sense, yet implementations are in chaos for lack of
> norms here, and a lot depends on cleaning things up.

> CSS superceded the FONT size system with 7 keyword sizes of its own,
> but the scheme is underspecified and has been badly botched in
> implementation.

This also suggests that the spec needs fixing and that the CSS WG
is the proper place to push.

Thanks for your comments, Todd. Let me know if you think
the CSS WG is the proper forum for promoting a proper implementation.

 - Ian

> [1] http://style.metrius.com/font_size_intervals/altintervals.html#st

Ian Jacobs (jacobs@w3.org)   http://www.w3.org/People/Jacobs
Tel/Fax:                     +1 212 684-1814
Cell:                        +1 917 450-8783
Received on Monday, 22 November 1999 12:39:53 UTC

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