Please provide an example ENGINE INDEX sim var?

GENERAL ENG MASTER ALTERNATOR:index | The alternator (generator) switch
position, true if the switch is ON. Requires an engine index, and the use of
an alternator index when referencing.
Please provide an example or a link to how this engine Index is to be set.
similar to a K:2 setup with circuit breakers bus Index?

index is a value between and 1 and n, n being the number of engines. For
example, GENERAL ENG MASTER ALTERNATOR:1 will give you the status of the
alternator linked to engine 1.

what is the “and the use of an alternator index when referencing.” so the
description is wrong?