Problem with Event Syntax

I hope someone can help me with syntax, common throughout the events and simvars, such as:
and [0]: New reference altitude
and [1]: Index
I presume this decrements the reference altitude (whatever that is) but, if so, how big is the decrement? And, how do the [0] and [1] come into play? A couple of examples would be most helpful.
Thanks in advance.

There are no parameters to this event.

The parameters mentioned in the event documentation are most probably just a copy paste leftover. Those parameters are only used in the AP_ALT_VAR_SET_… event.

Hello: I was more interested in the syntax of the [0] & [1] than in that specific event. The list of Events is littered with similar cases. So, by the question, I was asking what the [0] & [1] nomenclature meant, and how to use it, especially when [0] means one thing and [1] refers to an Index. Thanks.

It depends on what tool you are using. You did not give any information about in your post!

I am using Air Manager but the syntax is used in the descriptions of a great many SimVars and I think Events as well.