what is a! and why we use it in expressions?

Hi there,

AFAIK, a! is used to precisely identify which function belongs to Appian and which functions do not (custom functions, expression rules, interfaces, decisions, etc). However, there are some functions that do not start with a! even after being Appian's native functions.

One of our Trainers once jokingly said "fn! is the domain for the set of functions, and a! is the domain for another set of functions!"