What should we do if you reference outside a supported range?

["David A. Wheeler" <dwheeler@dwheeler.com>]

If an application does not support some column (say "ZZZ"), and a formula
tries to reference it (e.g., [.ZZZ1]), what should happen?

The "obvious" answer "that is an Error".  Should we specifically say that?
Should we permit an alternative (e.g., presuming that they are empty cells)?

Anything else?

I'd like to clearly document what happens in this case.

--- David A. Wheeler