code: def phantom_decorate(f, get_or_add):
      
      def wrapper(*args):
          self, pkt, s = args[:3]
          if phantom_mode(pkt):
              if get_or_add:
                  return s, self.phantom_value
              return s
          return f(*args)
      return wrapper
docs: Decorator for version-dependent fields.
      If get_or_add is True (means get), we return s, self.phantom_value.
      If it is False (means add), we return s.