I am trying to learn where each of the five events can be called.
I successfully found out where ElementEventHandler are assigned and called. (When you select a symbol)
I successfully found out where TimelineEventHandler are assigned and called. (When you assign a script to the timeline)
I successfully found out where DocumentEventHandler are assigned and called. (in the document tab you click event handlers and call it from there.)
A normal function can have an arbitrary number of arguments so it cannot be assigned directly to a Run JavaScript action. Instead, you can call it in any other event handler functions.
For example, if two or more event handlers need to do a common task, you can add a normal function to do that task and call it in those handlers.