Steps to reproduce:

1. Open: https://www.zabbix.com/documentation/current/en/manual/appendix/functions/aggregate
2. 
3. Open: https://www.zabbix.com/documentation/current/en/manual/appendix/functions/aggregate/foreach
4. Find no 'Except where stated otherwise, all functions listed here are supported'.

Result:
Foreach are not supposed to work with triggers.

Expected:
Exact definition where and what should work.