[AccessD] Is operator

All documentation refers to the Is operator as used to compare two object
reference variables. But, we also use it in simple criteria expressions in
queries, etc.

So, what Is really?

It's a comparison operator, but why does documentation define it as a
comparison operator for objects when we obviously use it for other things?
The documentation just may be poor in implying that Is works "only with" --
or it's very specific and there's more to it than I understand.

Susan H.