"When I work with TRIGGERs, which is rare"

Evidently, even some experts do use triggers.

"I normally limit them to at most one per operation per TRIGGER"

Great! So do I! So far so good. I guess I'm still in the good graces of some experts.

"in full ANSI/ISO SQL, we do have schema level constraints, the CREATE ASSERTION statement, but that is another topic"

Not in PostgreSQL, we don't. Evidently some experts may not be perfect experts.