A unique string identifier for DialogBox and TaskDialog type dialogs in Revit. 
   Namespace:   Autodesk.Revit.UI.Events  
  Assembly:   RevitAPIUI  (in RevitAPIUI.dll) Version: 19.0.0.0 (19.0.0.405) 
  Since:  2017 
Syntax
Remarks
 The contents of this entry vary depending on the type of dialog which is shown: 
 - DialogBox: A unique string ID that can be used to identify those whihch dialog has been invoked.
 - TaskDialog: The customed string if TaskDialog.Id is set, empty string for default TaskDialog.Show(). For Revit-created dialog boxes, this should always have an assigned value.
 - Standard Message Boxes: this will be an empty string.