code: def app_errorhandler(self, error: Union[Type[Exception], int]) -> Callable:
          
          def decorator(func: Callable) -> Callable:
              self.record_once(lambda state: state.app.register_error_handler(error, func))
              return func
          return decorator
docs: Add an error handler function to the App.
  
          This is designed to be used as a decorator, and has the same
          arguments as :meth:`~quart.Quart.errorhandler`. It applies
          only to all errors. An example usage,
  
          .. code-block:: python
  
              blueprint = Blueprint(__name__)
              @blueprint.app_errorhandler(404)
              def not_found():
                  ...