In order to understand TeX better, and in order to procrastinate on stuff that is almost certainly more important, I'm slowly working my way through a YouTube series of Knuth explaining TeX82 internals and TeX: The Program (which I think describes TeX3).
I'm following it all… more or less. But it's too much to keep in my head, and (literate programming or not) I'm finding text to be a less-than-ideal format for getting a bigger picture of the code.
Is there somewhere a set of diagrams of the major elements of TeX's design—e.g. data structures, flow charts, state machines?