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Re: Z-Order and Tag Order Need to Match?


From: Duff Johnson
Date: May 27, 2020 11:58AM

> On May 27, 2020, at 13:34, < <EMAIL REMOVED> > < <EMAIL REMOVED> > wrote:
> As a member of the ISO committee that develops the PDF/UA standard, I think
> it was a good idea to push the industry to one centralized reading order,
> and so the tag tree was chosen as the primary reading order.

It was not "chosen" - tagged PDF is and has always been the only way to represent the semantics of PDF content to AT.

> But in the real world, there are too many non-compliant or semi-compliant
> technologies that choke on PDFs because of bad architectural reading orders.
> Just because we say "ABC must be so" in the standard, doesn't guarantee it
> will be so in real life.

The same technologies that cannot handle tagged PDF also cannot represent headings, tables, etc to the end user.

The only way to convey semantic structures from a PDF to an AT is tags. This is not to deny that some users benefit from tools that cannot represent correct semantics and logical reading order, but there are very good reasons why aligning content and tags is a "nice to have" and not a requirement.