On a page https://www.zabbix.com/documentation/2.0/manual/appendix/macros/supported_by_location
we have a lot of such macros. Some macros have useful description, I mean details about "...of the Nth item in the trigger expression that caused a notification"
I've counted 8 of them and they are related to notifications only.

But we have there a lot of other macros with similar syntax

and they supported not only for notifications !

Sometimes users can suppose that for example

could be used in item key parameters and should return a secondary host interface details.
A proof https://www.zabbix.com/forum/showthread.php?t=40581
By the secondary interface I mean a not main host interface.

To avoid such misunderstanding I suggest to add some general description of such macro syntax on pages:
https://www.zabbix.com/documentation/2.0/manual/appendix/macros/supported_by_location
https://www.zabbix.com/documentation/2.0/manual/config/notifications/action/operation/macros