Hello.

Our expectation that trigger expression with "and not" for these two cases will provide us the same result:

1) and not dayofweek()=6 and not dayofweek()=7

2) and not (dayofweek()=6 and dayofweek()=7)

First expression not work. Second work correctly.

There is no documentation for this case.

Only https://www.zabbix.com/documentation/current/en/manual/config/triggers/expression

with explanation:

"not, and and or operators are case-sensitive and must be in lowercase. They also must be surrounded by spaces or parentheses."

Looks like parentheses is mandatory. Not "spaces or parentheses." -> "spaces and parentheses".

This mistake caused incident unfortunately. Please see attachment for example.