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[navigation] headers vs. nesting

From: Al Gilman <Alfred.S.Gilman@IEEE.org>
Date: Thu, 17 May 2007 14:08:37 -0400
Message-Id: <p06110409c272454dcac2@[192.168.1.100]>
To: wai-xtech@w3.org


** Question: how to integrate levels explicit in html:h1 etc. with the
nesting discovered from the parse tree, in creating a "best practice"
Table of Contents for a page?

** Discussion:

Authors will use HTML header elements and ARIA @aaa:labelledby
in weird and wondrous ways, and AT won't be able to provide
the highest and best structural navigation to their users unless we
say something about how these two techniques combine.

* Layout concept:

I can imagine a visual or braille layout for a Table of Navigation (a
jump-to-enabled Table of Contents) that is derived from both
the containment relationships in the parse tree and the header
levels in header elements that follows the following rules:

Sub-elements are listed after and indented from their super-elements.

The indenting is normalized so that all Hn levels used in the document
correspond to vertically-aligned staring positions for the headers
so marked up.  In fact, while not demanding exact metric equivalence
in the horizontal indenting from H1 to H2, H2 to H3, etc, if the
use in the page is gapped, such as using H1, H2, H3 and H5 without
H4, the gap between H3 and H4 alignment lines should be extended
to allude to the missing level.

This means that there may be fractional indents for containers that
don't have Hn elements that they are labelled by.  This could become
a burden in Braille where one- and two-cell indents are the norm.
Braille presentation might lose the distinction between an Hn and
a section label hooked by @aaa:labelledby in its presentation effects.

In any modality of styling, section labels that are not Hn elements will have
either more recessive text effects than the explicit Hn element headers,
or will be distinguished by a brief prefix category announcement.

Missing indent levels may or may not be indicated by a stub or minimized
entry in the layout of the Table of Navigation.

Author tools may bark at authors for this "improper" use of header
levels, but User Agents should cope and extract a tree that is as
close to what the author gave them as is practical, and affords a
consistent frame of reference as the user moves around the page.
Even if the UA has to make some arbitrary decisions in bashing the
page into a navigable tree, it should do so because the user can
remember how it was announced the last time they passed by this
part of the page.

* Voicing concept:

Mostly, the effective section label needs to be voiced.  If the AT
decides it wants a category name for the current container that has
that label, it can announce "section labelled ..." or invent any other
term it wants, but it should be different from the way it announces
an H3, for example.

** Comments?

Al
Received on Thursday, 17 May 2007 18:08:56 GMT

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