The ID of the tagged local element, if any. If the tag is tagged on a subelement of local element, it returns the element ID. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 18.0.0.0 (18.2.0.0) 
  Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 18.0.0.0 (18.2.0.0)