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Re: PDF reading order and tag order

for

From: Alastair Campbell
Date: Jun 12, 2017 5:07AM

Hi Duff,

On this bit:
> Software that does not use tagged PDF (such as the Reflow feature in
Adobe Reader, for example) has to guess to infer a reading-order.

That came up in a discussion about WCAG 2.1 where we are looking at
increasing the resize-content aspect:
https://github.com/w3c/wcag21/issues/77#issuecomment-306385027

Are there techniques for defining (or at least controlling) the order in
which a PDF document is reflowed?

Cheers,

-Alastair

On Wed, Jun 7, 2017 at 7:51 PM, Duff Johnson < <EMAIL REMOVED> > wrote:

> A couple of things to be said...
>
> > Add braille printers to the lineup that use the order panel, not the
> tags. At least that was the case a couple of years ago when some of our
> clients with visitors centers were printing braille visitor guides.
>
> No-one should be under the impression that there's anything about the
> "order panel" that's truly about accessibility. For the purposes of this
> conversation it can be boiled down as follows:
>
> - The 'order panel- in Acrobat Professional denotes the sequence in which
> objects are painted onto the page. This is fundamentally orthogonal to the
> question of 'reading order-, which is denoted *entirely* by the use of
> "tagged PDF-. Often, they align to one degree or another. In most cases,
> there are significant discontinuities.
>
> - Software either uses or does not use 'tagged PDF-
>
> - Software that does not use tagged PDF (such as the Reflow feature in
> Adobe Reader, for example) has to guess to infer a reading-order. Leaving
> such accessibility basics up to software heuristics is manifestly NOT what
> accessibility is all about.
>
> - As a concession to today's world where many AT software don't 'do-
> tagged PDF, Bevi's right that aligning content order and tag order to the
> extent possible creates value for users who are saddled with the
> aforementioned software.
>
> > Talking with a colleague, it's hard for us to know which technologies
> use which order and there's no central source of information that covers
> all of the A.T. on the market today. Plus people might be using older A.T.
> that could be using the order, not the tags.
>
> There's nothing fixed about this. While current-generation AT software may
> not used tagged PDF, the next version of that software may do so. But not,
> of course, if people don't ask for it.
>
> > Our recommendation: try to get both to synch up, but if you have to
> compromise, make the tags accurate and the order can slide a bit. Not too
> much, but a bit.
>
> Since the 'order panel- can't accommodate discontinuous content... or even a
> paragraph that spans two pages, compromise is indeed essential.
>
> It's just as important to educate service bureaus and the like to point
> out to them that if they are getting their 'reading order- from
> page-content instead of from tags (when present) they are doing their
> end-users a disservice.
>
> Trying to design a PDF file to accommodate software that does not use PDF
> accessibility is something one should consider carefully, and preferably,
> reject. In my view, it makes more sense to insist on software that actually
> understands accessible PDF files (contact the vendor!!!) rather than invest
> in the prodigious amounts of labor required to make PDF files sort-of
> 'work- with manifestly substandard software.
>
> Duff.
>
>
>
> >