code: def register_related(cls, related_name):
          
  
          if not hasattr(cls, '_clone_related'):
              cls._clone_related = []
  
          if type(cls._clone_related) != type([]):
              cls._clone_related = list(cls._clone_related)
  
          if not related_name in cls._clone_related:
              cls._clone_related.append(related_name)
docs: Register a related item that should be cloned
          when this model is.
  
          :param related_name: Use the name you would use in filtering
              i.e.: book not book_set.