code: def build_key(self) -> Tuple[bool, int]:
          
          if self.map is None:
              raise RuntimeError(f"{self!r} is not bound to a Map")
          return (not bool(self.defaults), -sum(1 for weight in self._weights if weight.converter))
docs: A Key to sort the rules by weight for building.
  
          The key leads to ordering:
  
           - By routes with defaults first, as these must be evaulated
             for building before ones without.
           - Then the more complex routes (most converted parts).