def register(self, key, value, exist_ok=False):
        """
        Register a new model in this mapping.
        """
        if hasattr(key, "__name__") and key.__name__ in self._reverse_config_mapping:
            model_type = self._reverse_config_mapping[key.__name__]
            if model_type in self._model_mapping.keys() and not exist_ok:
                raise ValueError(f"'{key}' is already used by a Transformers model.")

        self._extra_content[key] = value

        Register a new model in this mapping.
        
dpkd/transformers/src/transformers/models/auto/auto_factory.py