Determine whether the family has been defined by the user. 
   Namespace:   Autodesk.Revit.DB  
  Assembly:   RevitAPI  (in RevitAPI.dll) Version: 17.0.0.0 (17.0.1090.0) 
  Since:  2015 
Syntax
Remarks
 Some families are created internally and cannot be saved or reloaded. This function will return False for such internal families.