Using <System.Obsolete("Warning Message", false)> you can deprecate controls. My situation is similiar, but a little different. I have values being assigned to y custom object's properties that I would like to validate with RegEx.

I.E.
They pass "Cheesetype=cheddar;Cracker=wheatthin" to a style property during design (as a constant expression); I would like to be able to use similiar design-time functionality to say (based on regex), use the object's property "Cheesetype" instead of inline attributes as a warning.

Any ideas or a direction?