Even better than in-line validation is on-form not-letting-you-screw-up-in-the-first-place.

So if items can have only unique combinations of categories-- the column A and column B pair must be unique-- when a user selects something in column A, anything that had been previously selected with column A in column B should become unavailable to select.

Comments

Coupon Code Swap’s picture

Coupon Code Swap CreditAttribution: Coupon Code Swap commented

I can see this working for radio forms, select lists etc. when there are predefined options available. It would be the most elegant way of handling those form items. But what about free-form text fields? My main use would be validating a text field, based on a previously selected term. After the user finishes typing, they would be presented with a message either confirming that the value is unique for the term selected or warning that it is duplicate.