> I think that textbooks, math textbooks in particular, are an example where print publishing does a disservice. (I'm counting PDFs here too.) By having to lay everything out in print form, you have to clutter up your explanations with examples and footnotes that take up physical room. .

I agree with your sentiment. Although, I believe there is bit of problem of generalizing it to a wider field. Surely, you can make explorables with Linear Algebra, Trigonometry, Geometry, Number Theory etc, but there still exists a lot of mathematical fields, where such explanation using visualization is pretty difficult. It takes a lot of time to come up good explanations, while even longer for interactive explorables.

> All in all, I'd love to see more interactive textbooks. We've got this really expressive kind of document via the web. I think we should be taking advantage of it more.

This is something I have spent the last 4 years of my life building. I designed an alternative way of writing interactive books that takes a different approach than using just explorables. It's a conversational way of learning subjects designed for auto-didacts.

You interact (converse?) with the book and learn gradually. You can of course embed explorables into it (which I am planning to for upcoming linear algebra / discrete mathematics course), but the general process can still be generalized to any field. And if you are a LaTeX fan, you are in luck as all your notes are compiled as a Tufte-Latex Notebook. The medium is called Primer, homage to the diamond age.

You can checkout Primer here https://primerlabs.io.

A comic-based guide to understand how Primer helps you learn effectively: https://primerlabs.io/comics/introducing-primer-comics/