I figure the way to encourage more folks to try their hand at modding is to make it as easy as possible for their questions to get answers. I don't have all the answers, but there is always someone who does, or knows where they are.
So let this be the place where we do that! #HopeThisIsntOverzealous
Here's a better explanation:
ROOT
Whoever or whatever the event/decision goes to. In an on_action, the game looks for various triggers (on_birth, on_pregnancy, on_death, etc) and then fires (if the event is guaranteed) for that person in either a character_event, long_character_event, or narrative_event. Whoever triggered it and got the event will be ROOT (some exceptions apply, see the on_actions file).
This also applies to provinces, in the case of province_event. A prov