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Re: PDFs: Logical Reading Order and Tags

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From: Duff Johnson
Date: Jun 1, 2016 7:20AM

> When we get a PDF generated out of InDesign the tags are usually non-HTML5-standard tags in a jumbled order.

Two things…

1) PDF does not use the same set of structure elements ("tags" in HTML-speak) as HTML. PDF is not HTML; HTML is not PDF.

2) If the logical ordering of tags in the PDF file is incorrect then the InDesign file was not authored properly with respect to accessibility. There are, sadly, still numerous ‘gotchas' in the InDesign world that can make this a pain.

A tool InDesign folks should consider is Axaio's MadeToTag, which offers a lot of help in accessible PDF authoring from InDesign.

> Yet often the logical reading order is fine, or can easily be fixed using the Acrobat tool for doing so. Testing in a screen reader like JAWS or NVDA seems to yield a pass as well- the content is read in the correct order.

In PDF, logical structure elements (commonly known as tags) determine the logical reading order of the content. Thus, you can look at the sequence of tags (or export to HTML, or use a free tool such as pdfGoHTML) to review the logical ordering of the content.

Of course, you can also use a screen-reader or other AT that understands accessible PDF. You CANNOT, however, use software such as Adobe Acrobat's Read Out Loud or Reflow features to test this, since these features do ***not*** at this present time understand accessible PDF. :-(

> How important is it that the tags themselves be (1) rearranged to match the logical reading order

Critical. Contra the erroneous advice offered in WAI's PDF Technique 3, there is no accessibility without structure elements (tags) in correct logical reading order.

(Sidenote: the errors in the PDF3 technique are one of the most serious causes of confusion worldwide on this subject.)

> , and (2) thoroughly reworked to use only HTML5 standard tags?

As above… PDF has its own set of structure elements; they are not the same as HTML's set for a variety of reasons. NEVER attempt to use HTML5 tags in a PDF document unless you are prepared to role-map your "HTML5" tags to PDF's standard structure elements.

> I imagine this turns on the question whether there are AT tools other than JAWS and NVDA that depend on these tags being standard and reordered.

What's critical is that PDF tags are employed properly and predictably. This means using PDF tags for PDF files.

I hope this helps.

All the best,

Duff Johnson

PDF Association Executive Director
ISO 32000 (PDF) Intl. Project Co-Leader, US Chair
ISO 14289 (PDF/UA) Intl. Project Co-Leader, US Chair
Independent Consultant

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