Thread:Help talk:Special property Allows value/Non-allowed values revisited

As Yaron has remarked above, when a value is not allowed, it is simply not assigned.

The only hint that a user gets when he uses such a value is the warning sign assigning the value using Foo::bar. However, when using, there is no feedback to the user. Or is there? Or should one implement that?

Otherwise, is it possible to get a list of pages that assign bad values or something like that? Like a special property "uses bad value" or the like? Or would it be possible/make sense to implement that? Already answering my own question: Property:Has improper value for. Still, what about adding an attribute to to allow outputting the warning sign in case of an error?