Oh, documenting S2! I look forward to the results of this project. It's been so long since I worked seriously with S2 that I barely remember how to use it. I do remember that while I was hanging out at s2flexisquares I made some valiant efforts at demonstrating how NOT to explain S2. Still, I think most of the useful documentation was always found in the various layout help comms. afuna and I made loads of tutorials that were specific to Flexible Squares, but since most people who asked for help were starting from square one there also had to be general tutorials for explaining the basics. Like, for the whole "understanding layers" thing, I always liked kentucka's What are layers and styles?, especially the helpful graphics.

Those comms touch very little on actually helping people understand the language, though, as most of the people asking for help are interested in copy&paste solutions, not deeper understanding. For that I can't think of any great pre-existing docs. My own posts on the topic were more like "isa and as, yay!!!" Most layout help comms do have a tonne of examples of how to apply the language to make awesome things happen, though, so that might be useful reading when writing a cookbook.

(reposted to correct stuff!)