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Nesting Heading levels in PDFs

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From: Alan Zaitchik
Date: Jul 7, 2017 6:06AM

I'm working on PDFs where often a less important heading precedes a more
important heading in terms of its sequential placement on the page. To
correctly assign levels in terms of importance thus requires me to place
an <H2> ahead of the <H1> (for example) - or I must re-order the tags so
that the <H1> is ahead of the <H2> in the tag order even though it is
later in the (visual) reading order.
My understanding is that WCAG 2.0 does not forbid having an H2 tag ahead
of an H1 tag.(See
https://www.w3.org/WAI/WCAG20/quickref/#qr-navigation-mechanisms-descriptiv
e. Since our project is funded by HHS I also checked their requirements in
https://www.hhs.gov/web/section-508/making-files-accessible/checklist/pdf/i
ndex.html, where there is nothing explicitly stated about this.) Indeed,
although the Acrobat Accessibility Checker flags my re-ordering as
"incorrectly nested" it also notes in the Explanation that the strict
ordering is only an 'advisory guideline'.
Still...  Can anyone confirm that my understanding is correct about these
matters? It would be reassuring to know that I can safely ignore Acrobat's
failure message and that HHS (or best practices in general) are
comfortable with prioritizing semantically correct leveling of headings
and keeping to the reading order ahead of brute force reordering heading
tags according to their levels and ignoring placement on the page.
Hope the above makes sense.
Thanks,
Alan