I've only just skimmed through this. And it's a subject I already know so I can't tell if it's actually a good resource. However, my initial impression is that I love it.<p>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. Here, the examples are toggle-able. If I _want_ to explore an example, I can. But I don't need to. This kind of thing is especially helpful when reviewing content for, say, a test rather than learning it for the first time.<p>Also finding things in textbooks is a real pain. It's difficult to index things in a helpful way, so you just have these counting schemes in LaTeX that increment for every definition, theorem, etc. I'd love to be able to tag things then search the tags.<p>And that says nothing for when you want to explain something that's difficult with static images. Being able to interact with animations by zooming, panning, pausing, slowing down, speeding up, etc. is a boon. (I don't think I actually saw an example of a non-static image here, but I think my point still stands.)<p>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.