Re: Does 5.1 absolutely require TH?

> Does 5.1 require the addition of table cells if the author had not 
otherwise planned to include headers?

The answer to your question is that neither WCAG nor 508 explicitly 
defines the difference between data tables and layout table or layout CSS 
- when you must use which is not declared.  The Evaluation & Repair 
working group has been wrestling with this for a long time.  Automated 
checker developers have been working on this for years.  I know of a 
limited definition of data table in WCAG 2.0 draft as: "Groups of rows or 
columns are labeled with headers - see Guideline 2.1 examples 
(informative). 

Maybe you should suggest a definition for "layout" and "data table" to be 
added to WCAG 2.0

What I said on the 508 list was:
... my rule of thumb is once the number of columns exceed 3 - it depends, 
but once it exceeds 7 columns you definitely need column headings, and 
therefore <th>'s

I think we might be able to reach consensus that you are not required to 
use <th>'s on 2 or 3 columns of data, but that it is recommend as a best 
practice to be explicit with <th>'s even on 2 & 3 column information. 
Maybe we could even reach consensus on "7 or more columns of information 
should be marked up with <th>'s".

by the way, the definition needs to handle the case where the developer 
incorrectly codes the multi-column information with CSS, but should have 
used HTML table mark-up instead.

Regards,
Phill Jenkins
IBM Worldwide Accessibility Center
http://www.ibm.com/able