Indicates whether the event is being cancelled. 
   Namespace:   Autodesk.Revit.DB.Events  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 2015.0.0.0 (2015.0.0.0) 
  Since:  2011 
Syntax
Remarks
 If the event is cancellable and an event delegate wishes to cancel the event, it may call the Cancel() method if it is available for a particular event's arguments.