The tagging project and beamer

I talked a little while ago about work that the LaTeX Project team are doing on creating tagged PDFs automatically from ‘standard’ LaTeX sources. I promised to talk about how this might impact beamer, and was recently reminded about that.

The nature of presentations

The first thing to say is that beamer (or rather presentations/slides) are a tricky topic. There is lots of (legal) pressure for people doing teaching to provide accessible resources, which includes slides (at least to some extent). On the other hand, there are a lot of structural things that make presentations a lot more complexes from a tagging point of view than more classical ‘documents’ (articles and the like). Presentations also tend to be limited-life documents: most people will revise slides each time they present, unlike an article that once published is basically ‘frozen’. That means that the idea that documents have to work ‘unchanged’ isn’t quite the same for beamer as it is for say the article class. But work does need to be done.

Work so far

The wider reason that tagging currently doesn’t work at all with beamer is that internally, the class is ‘interesting’. There is a lot of re-boxing material, and very little in the way of semantic flow. The class also does things its own way: that means that in a lot of places, standard LaTeX code is ignored or overwritten, and so the work being done on tagging in general doesn’t apply.

Along with other members of the team, I’ve looked at beamer in detail and we’ve concluded that ‘upgrading’ to tagging isn’t realistic in the current class. What’s needed instead is a beamer replacement, taking forward key ideas (and as much of the syntax as we can), but starting from the idea of including tagging support.

Future plans

Writing something that covers everything beamer does will take a long time, so that’s not the initial target. Rather, we want to pick off specific areas. First, the simple idea of a tagged structure that looks like a slide, then moving on to simple overlays before even looking at the ‘visual effects’ that people like to use in presentations. At the moment, the code for this effort is not public, but once there is something that works for simple slides (like my own teaching), that will change.

As well as the LaTeX Project team, there are a few other people with an interest in this work. So I hope I can get things moving along once the basics are in place.

Document structure

There is a particular point to consider when tagging is that it makes little sense to try to tag slides themselves, at least unless they use no animations. If you think about a typical beamer slide such as

\begin{frame}
  \frametitle{Some things I did}
  \begin{itemize}[<+->]
    \item One
    \item Two
    \item Three
  \end{itemize}
\end{frame}

the resulting PDF will have three pages, each of which contains at least one of the list items, and all of which have the same title. For tagging/reuse, we almost certainly don’t want that: we want the ‘flattened’ version (as you’d have in an handout).

That looks OK if you take a simple example, but once authors start using overlays to swap one image for another ‘in place’, etc., it’s no longer clear what the right tagging might be. So part of the overall project here will be about working with users to explore what the answers are.

See also: Original Source by Joseph Wright