Id of the stair associated with the Reference Level for the multistory stairs. The standard stair is regarded as a definition to generate new stairs when extending multistory stairs to a different level height. 
   Namespace:   Autodesk.Revit.DB.Architecture  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 18.0.0.0 (18.2.0.0) 
  Since:  2018