FPSC is touted as a "no coding necessary" engine. I'm guessing that is at least part of the reason there has never been more than a "one-line" explanation for the conditions and actions. To my knowledge, with the exception of a few member-made scripting tutorials, there is no documentation except what you see in the manual.
It has always been up to those of the community most interested in the fpi language to test and explain the code. There is a great deal of trial and error, sometimes only to find that the particular condition or action has not been implemented in the engine.
Undocumented is an understatement. Welcome to the forum.
Best.