I have a form where there is a user preference for a display name. I would like to be able to check prior entries and enforce a unique value for this particular field and not allow a submission if the name is a duplicate. I've been poking around a little and see that something like frm_validate_field might be the right approach, but I'm at a bit of a loss about how to implement such a solution. (I know it would need to go in functions.php - I'm generally php capable, it's the interface into FF that's a bit confusing.)
Any pointers would be appreciated.