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

for

From: chagnon
Date: May 27, 2020 11:34AM

We've written extensively on this, and we guide our clients and students as
follows:

1. The PDF/UA-1 standard requires that ONLY the tag tree be used by
assistive technologies. All information, relationships, tags, reading order,
etc. should be in the tag tree. Therefore, only the tag tree needs to be
compliant.

2. However -- and it's a very critical "however" -- many technologies use
the architectural/construction order (the Z-Order, Order Panel, "blue Z
tool", whatever you want to call it) to "process" the PDF file. Some are
legacy assistive technologies, and others are common tech used by the
general population, such as smart phones and tablets used by students in
academia.

3. Plus, all technologies that read PDFs are affected by the
architectural/construction order in some way. It shows the
foundation-construction of the PDF, like the studs in a building's walls.

Therefore...
It's smart to put the architectural/construction order in "order" because
you'll accommodate the widest audience, regardless of what technology they
use, and regardless of whether it's a valid, PDF/UA-1 compliant processing
technology or not.

But it's not required per PDF/UA-1.

We urge our clients to aim to make the architectural order match, as closely
as possible, the tag tree order so that they coordinate and the document
works for everyone.

Sometimes that's not possible, due to the visual design and construction of
the PDF by the author, or sometimes that would incur an insane amount of
time and money to force it into compliance.

In those situations, get the architectural order into decent shape -- an
example, make sure headings and critical information on the page are in a
logical order, but the graphics and their captions can often fall to the
bottom of the order tree and the PDF will still be readable and
understandable.

Although the Sec. 508 federal regulation only requires PDF/UA-1 compliance
of PDF documents, any government agency, school, or college can mandate that
their PDFs go beyond the PDF/UA-1 standard. That's their right and choice.

I believe that the PDF/UA-1 standard missed the boat on the
architectural/construction order by mandating that only the tag tree provide
accessibility, and not giving any guidance or requirements for the other
reading order.

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.

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.

No one has enforced compliance on the manufacturers of screen readers,
dyslexia software, mobility devices, and other assistive technologies.

No one can prevent someone from using a free PDF viewer on a Kindle, for
example, or use Apple's Preview software on a Mac. We can't regulate WHAT
technology people will use.

In the end, when the user uses XYZ technology, the PDF still has to work.

So make the architectural/construction order work.

Just my 2 cents' worth.

-Bevi
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Bevi Chagnon, founder/CEO | <EMAIL REMOVED>
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PubCom: Technologists for Accessible Design + Publishing
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