After discovering the toggle command available in MathJax, I immediately went to asked the capable people of tex.stackexchange whether this could be done inside a PDF file. And indeed: It can be done!

```
\documentclass{article}
\usepackage{animate}
\begin{document}
\begin{animateinline}[step]{1}
\strut$x=1$
\newframe
\strut$x=2$
\newframe
\strut$x=3$
\end{animateinline}
\end{document}
```

Now, what do I want with this package? I want to do abstract nonsense. A diagram-based proof should, in my opinion, be a slideshow. You start with the diagram that is your assumption and by simply interacting with the diagram (clicking it), in each step, a new arrow is constructed from some universal property.
I wanted to write a neat animated PDF with an abstract nonsense proof of the famous Snake Lemma, and there is a great book by Francis Borceux containing a proof, but unfortunately, I was unable to overcome a difficulty with the proof, so that will have to wait until someone answers my question.