[css3-layout] PFWG comment 1 of 2 on CSS Template Layout Module: Tab order (for sighted keyboard users).

The following is comment one of two from the Protocols and Formats
Working Group on the CSS Template Layout Module draft of 29 April 2010
<http://www.w3.org/TR/2010/WD-css3-layout-20100429/>. Approval to send
this as formal WG comments is recorded at
http://www.w3.org/2010/06/16-pf-minutes.html#item08. Thanks to Léonie
Watson for preparing these comments.

Current CSS techniques make it possible to separate the visual
presentation of a page from the source order. This can have both
positive and negative connotations for accessibility, and the CSS3
template layout module increases the potential for both.

The attached zip file contains a page with three examples:

1. Content priority source order, where the source order is content,
related content, navigation.
2. Visual priority source order, where the source order is navigation,
content, related content.
3. Complete mess source order, where the source order is related
content, navigation, content.

In each case, the visual presentation follows a typical layout for
sighted users. Navigation on the left, content in the middle, and
related content on the right.

Examples 1 and 3 use a source order that differs from the visual
presentation. This causes the tab order through the page to jump around,
particularly in example 3. Sighted people who only use a keyboard may
find this movement confusing.

On the other hand, example 1 uses a source order that is helpful to
screen reader users. The content is placed first in the source order,
without disrupting the visual presentation.

This isn't a new conundrum, but we're in a good position to encourage
best practice for accessibility amongst developers. We'd suggest adding
a short informative section to the template layout module that
references the following WCAG 2.0 success criteria:

1.3.2 Meaningful Sequence: When the sequence in which content is
presented affects its meaning, a correct reading sequence can be
programmatically determined. (Level A)
2.4.3 Focus Order: If a Web page can be navigated sequentially and the
navigation sequences affect meaning or operation, focusable components
receive focus in an order that preserves meaning and operability. (Level A)
-- 

Michael Cooper
Web Accessibility Specialist
World Wide Web Consortium, Web Accessibility Initiative
E-mail cooper@w3.org <mailto:cooper@w3.org>
Information Page <http://www.w3.org/People/cooper/>