Musings

PDF Accessibility

We physicists use a lot of PDF.

It’s the primary means of distribution of papers at the arXivs. It’s what we use to distribute class notes to students. The NSF requires our proposals be produced in PDF, … Indeed, pretty much anything with mathematical content is authored in TeX, and turned into a PDF file.

Accessibility is not something we think a lot about. Until, that is, we run into some regulation (either Government or University) that mandates that the documents we produce be accessible to the blind or vision-impared. If you’re Australian or Canadian, you may already have run afoul of these demands.

Sooner or later, we all surely will …

Joe Clark to the rescue.

I won’t repeat all the main points of his article. Instead, what I want to concentrate on is mathematical text, and our PDF content-creation tools.

First of all, everyone is, or should be, using pdftex. There used to be issues with handling figures in pdftex. But that’s a thing of the past. And pdftex offers so many advantages over tex→dvips→ghostscript (hypertext links, bookmarks, alpha-transparency, …) that there’s really no good reason to use the latter.

One important feature for accessibility is “tagged PDF,” which was introduced with PDF 1.4. By default, pdftex outputs PDF 1.4, but it doesn’t produce tags. You can retrofit tags into PDF 1.4 documents using recent versions of Acrobat. But it would be better if pdftex had the ability to generate them natively¹.

Accessibility of equations is something Joe didn’t touch upon at all, though he did allude to the shortcomings in the rendering of XHTML+MathML as a reason why they’re not going to replace PDF for mathematical texts anytime soon. But, whatever else you may say about it, MathML is accessible, and there’s at least one tool out there that will read MathML equations aloud. (Design Science received an NSF Grant for this effort, so, US readers, don’t think your Government doesn’t care about the issue.)

What about equations in PDF? Well, that’s the subject of another, more recent NSF Grant. What they plan to do, apparently, is embed MathML in the PDF file, and use the same technology, that allows their MathPlayer plugin to read MathML on the web, to read the MathML embedded in the PDF file.

MathML embedded in PDF … will some future version of pdftex support this? I don’t know. Ask Hàn Thể Thành. If not, there’s a serious possibility that, someday, you will be reduced to using MathType in Microsoft Word to produce accessible mathematical (PDF) documents.