About multiple copies feature of a field.

This is a very basic question about PDF form specifications.

I discovered one feature.

It is for making multiple copies of a field.

It can use to create multiple vertical and horizontal fields.
If I use it the new field name will be appended with ".1".

For example, if I copy 3 fields "A",
the original field name will became to "A.0" and new fields name became "A.1" and "A.2".

Is this only just a way to distinguish field names?

Or is there another reason?

Because this looks like a sort of array.