ButtonEvaluator is an option for ButtonBox which specifies where the expression constructed from ButtonFunction should be sent for evaluation.
The default setting is ButtonEvaluator->None.
Possible settings are:
With ButtonEvaluator->Automatic the expression to be evaluated can contain any Mathematica objects.
With ButtonEvaluator->None the expression can contain only the specific notebook commands supported by the front end. All these commands are in the context FrontEnd`. Expressions intended for processing purely by the front end must be wrapped with FrontEndExecute.