I don't want to call it after getting control back. I want the form to do that as part of its "validate" process, so it automatically interacts with the page and doesn't go through my code path that all is "submitted and validated".

The instructions show "validators" as being classes. Seems overkill to write a class, in a separate file in a structured directory branch I don't even have now, to do a simple comparison.

So, does this particular validator already exist, or is there a way to do equals between two fields (not just with constants) in the form definition, or can I just pass a code ref somewhere?