W3C home > Mailing lists > Public > wai-xtech@w3.org > May 2007

DRAFT Re: headers attribute debate

From: Al Gilman <Alfred.S.Gilman@IEEE.org>
Date: Mon, 28 May 2007 13:38:51 -0400
Message-Id: <p0611040dc280ad74fbfd@[]>
To: wai-xtech@w3.org


This is a quick draft of a possible statement on the accessibility
value of the 'headers' attribute as found in HTML4.

PFWG participants and colleagues from across the WAI are asked
to consider what our response should be to this request for



class="draft forDiscussion">


** summary

The function provided by the 'headers' attribute is to associate
table cells with information required for the understanding of the
cell contents; information that is provided 'centrally' in header
cells because it applies to more than one cell. Tables are different
from the bulk of web content where there is one path to ancestors and
such common information. In tables, there are common characteristics
both by row and by column.

1. The function is needed.

Metadata for Content Adaptation Workshop:


The relationship between (fragments of) content should be captured in metadata.
Where possible, metadata should be derived from the existing markup,...


WAI-ARIA States and Properties:

We would consider most related headers to fall within the meaning of
the aaa:labelledby attribute (occasionally aaa:describedby). The
existing 'headers' attribute provides this function in the context of
HTML tables.


2. The markup works.

An independent review by the U.S. Department of Justice for the Federal
Statistics workshop on accessible tables found that 'headers' was effective
in getting needed header information to consumers, as compared with
'scope' which was not well supported.


3. The path forward.

Starting from scratch, the broader @labelledby and @describedby
relationships are still needed. And leaf-by-leaf markup with this
bottom-up facility, while still needed to cover corner cases, could
be used less frequency if structural reforms were introduced such as
nestable row-groups in place of the present awkward 'tbody' at one
level only. @headers doesn't meet the full requirements across the
board (in and out of tables). @labelledby and @describedby could
convey all the information currently handled by @headers.

But we are not starting from scratch. There is an immense user base
of many sources as well as many sinks for HTML. So a measured
migration at the fastest would be appropriate.

In any case, the function is needed, and this current markup is
delivering the needed function. If we are to work this attribute out
of the system, it must be because it is being replaced with something
better, and via an orderly transition.

** details.

4. AT have small markets; they can only afford easy algorithms.

The reason that 'headers' got picked up rapidly and 'scope' didn't
was in part the following peformance comparison:

The screen reader had a table cell in its sights, and had received
a 'hunh?' query from its user.  It needed to contextualize this table
cell.  To answer this query by 'scope' the AT would have to search
the table for TH cells (often misused for styling) and then check
the 'scope' on each.  If the author used 'headers' there was an
attribute on the object at hand pointing to a short list of what
more to say.  Need I say more?

5. Yes, more could be done with algorithmics.  At the FedStats
workshop I was surprised to realize that what they characterized
as 'complex tables' were not, in my over-math-educated mind,
complex.  They were fully regular relations, with tree-form indices
associated with the rows and/or columns.  There was a hierarchical
structure to the categories represented by rows or columns and
groups of rows or columns.  There was no irrregularity in the structure.

On the other hand, the 'irregular tables' that we forced 'headers'
into the markup do exist in the wild.  These tables have "variant
record structure" where some of the fields are re-cast to new
headers on the fly within the table.  Also cases where two triangular
arrays are packed into one rectangular display, and there is a critical
diagonal -- on one side one refers to the left hand header, on the
other side to the right; and similarly for top/bottom headers.  There
were also train timetables that were weirder than this.  They overlaid
two mathematical relations (Eastbound and Wesbound timetables, for
example) re-using some fields.  These can be modeled by casting
cells in the roles of data and headers, but not with the coarse granularity
afforded by 'scope.'

Rationale at the time of HTML4:

Philosophy behind 'headers' as 'lowest level language' that covers the
corner cases:

Train timetable with some interior header data that applies to the left, some
to the right:


4.  There's room for further normalization in the space of required information
See in particular the strong appeal for anywhere-in-the-page LINK and META


5. (recap)

The genuine requirement is broader; a re-engineered solution could
deliver superior usability and authorability. But we are not starting
from scratch. There is a disability constituency that currently uses
and depends on this feature: anyone offering to remove it should be
expected to demonstrate that the replacement works better and is in


At 6:06 PM -0500 27 05 2007, Laura Carlson wrote:
>Patrick H. Lauke wrote:
>>With regards to the recent debate over the (removal, or
>>non-inclusion,  or "not-yet-included-until-proven-useful") headers
>>attribute: in areas  where potential impact on accessibility has been
>>identified by a group  member, further advice should probably be
>>sought from WAI and the PFWG,  as per charter (see email below from
>>Judy Brewer).
>The HTML 5 working group is indeed questioning the usefulness of
>marking up id/headers in complex tables. In fact the headers attribute
>is not currently in the HTML 5 specification.
>Advice from WAI and the PFWG on the potential accessibility impact of
>the absence of the headers attribute for HTML 5 would be appreciated.
>The following are related HTML 5 public-html and www-html
>posts/threads by HTML 5 working group members:
>Related Working Group member blog posts:
>Bruce Lawson:
>Roger Johansson:
>Thank you,
>>-------- Original Message --------
>>Subject: Re: WAI mandate to work with other WGs?
>>Date: Thu, 24 May 2007 00:49:53 -0400
>>From: Judy Brewer <jbrewer@w3.org>
>>To: Patrick H. Lauke <redux@splintered.co.uk>
>>CC: WAI Interest Group <w3c-wai-ig@w3.org>,	Al Gilman
>><alfred.s.gilman@ieee.org>, Michael Cooper <cooper@w3.org>
>>Here is additional information on your question about what role WAI
>>has in working with other W3C Working Groups to ensure the
>>accessibility of W3C specifications currently under development.
>>WAI's Protocols and Formats Working Group (PFWG) has, as part of its
>>mission, reviewing specifications under development in other W3C
>>Working Groups in to ensure consideration of accessibility-related
>>needs. PFWG's home page is at
>>          http://www.w3.org/WAI/PF/
>>Its charter, describing its scope of work is available
>>          http://www.w3.org/WAI/PF/charter200612
>>and there is a page describing participation
>>          http://www.w3.org/WAI/PF/participation.html
>>For the purpose you describe, participation on the wai-xtech list
>>(see the PFWG participation page above) would be a good place to
>>discuss accessibility issues that you are tracking in the HTML
>>Working Group. Because of the volume of work that PFWG needs to
>>monitor, it is helpful to have people on wai-xtech monitoring the
>>HTML WG traffic, and catching issues that need discussion.
>>In addition, the HTML WG has requirements in their charter to work
>>with WAI, and
>>PFWG in particular:
>>          http://www.w3.org/2007/03/HTML-WG-charter.html#coordination
>>I've copying Al Gilman, Chair of PFWG; and Michael Cooper, Staff
>>Contact for PFWG; so that you can also be in touch with them as
>>- Judy
>>Patrick H. Lauke
>Laura L. Carlson
>Information Technology Systems and Services
>University of Minnesota Duluth
>Duluth, MN U.S.A. 55812-3009
Received on Monday, 28 May 2007 17:39:04 UTC

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