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

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From: Paul Rayius
Date: May 27, 2020 12:36PM

Hi Ilana,
There's often a lot of question/ debate about this. When it comes to PDF standards (both ISO 32000 and PDF/UA, as well as WCAG 2.0 and 2.1) they're all quite clear that the reading order in a PDF shall be determined by the order of the tags. (To be more clear, WCAG doesn't specify the reading order "rules" for PDF but does provide some guidance in the WCAG Techniques.)

The confusion comes into play because some assistive technologies don't actually follow the standards and so they'll read content from "other areas" in a PDF - for example from the Content and or "Z-Order" pane in Acrobat. (The "Z-Order" pane is the one labeled "Order" but many people call it the "Z-Order" because of the "Z" in the icon.)

The problem, however, is that as accessible document creators and/or remediators, we can't possibly be called on to remediate according to how a particular processor or AT will handle a PDF. In fact, to that point, one of the great things about WCAG is that it's intended for accessibility while being technology independent. Personally, I think it's time for PDF processors and AT developers to be held accountable and that their products should adhere to the standards that are not only available but also achievable. But, that's my soapbox.

I hope this helps to clarify, though, that the reading order in a PDF is to be determined by the order of the Tags and not the "Z-Order."

Best,
Paul

Paul Rayius
Director of Training
CommonLook