Thank you, yes, it's not so much finding the code I need to modify that's the problem, as understanding how any given single thing fits into the Emacs C source

Thank you, yes, it's not so much finding the code I need to modify that's the problem, as understanding how any given single thing fits into the Emacs C source as a whole. Hacking the Lisp side I don't really have a problem with -- but if I want to, for example, extend the MESSAGE primitive so that it can check a list of messages not to emit in the minibuffer, things get very hairy, very fast. A general overview of what's what, and where, in the C source, would be extremely useful, and I haven't had much luck finding anything like that in the source distribution or online. (And, yes, I have read etc/CONTRIBUTE, etc/DEBUG, and (Info)Elisp/GNU Emacs Internals/*. And I'm pretty sure doing what I'm talking about doing to MESSAGE would be a bad idea, because it'd require a call up into Lisp space every time the primitive gets called, which can be extremely frequent especially during initialization. But I know somebody who'd like to have that functionality available, and it seemed like a relatively simple place to start, until I tried actually doing it.)