As I work through the code trying to make mods, the most time consuming task is trying to find where a constant is defined or which module to look into.

Has anyone put together a short summary of what each PHP module does? Granted most are obvious at high level but when one starts chasing code some of the includes and what they are doing is not always so obvious.

Secondly and along the same lines, is there data definitions catalog listing each data term and in which file it is defined?