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PDF Table column headers and scope attribute

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From: Alan Zaitchik
Date: Mar 16, 2023 9:00AM

I’ve told PDF developers for years that data table column header TH cells require scope set to “column” (unless IDs and the headers array are used to create associations). This advice was based on Matterhorn 15-003. I also seem to recall the old PAC-3 flagging it as a failure if scope isn't specified, although my memory might be wrong there.
What I'm now finding, however, is that for simple (regular) tables even when scope is not specified JAWS and NVDA consistently and correctly read the table headers; they correctly figure out that the TH cells have a column scope. Not only that, PAC 2021 and Acrobat A11y Checker don't report a failure. (Haven't yet checked with CommonLook or Crawford tools or others.) SO I'm wondering if this requirement makes a difference for these simple cases and whether it's even a formal PDF/UA requirement!
My questions are:
1. Can anyone point to a “significant AT product and PDF reader combination“ that does not implicitly assign correct scope when it is not explicitly coded?
2. Is the absence of the scoped attribute (when IDs and Header array mechanism is not used) a “formal failure” of PDF/UA accessibility? What is the normative status of the Matterhorn protocol?
3. Even if this is deemed a failure, might the priority of fixing this failure anyway be considered very low given my observations about JAWS and NVDA (and PAC 2021) not caring? Note again that I am NOT talking about complex tables, just simple regular tables on a single PDF page, no merged cells with colspan>1 or rowspan>1, etc., etc.

All feedback welcome!

A
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