If I understand this
The class of the object the event is applied to, four characters or a unique string. When an event applies to multiple types of objects, you use the event class parameter to distinguish which object this Notifier applies to. For example, the Make event (�Mk�) applies to documents (�Dcmn�), channels (�Chnl�) and other objects.
correctly the class in the case of a Warp transformation would have to be a Layer or a Channel.