docs: def on_error_default(self, exception_handler):
          """Decorator to define a default error handler for SocketIO events.
  
          This decorator can be applied to a function that acts as a default
          error handler for any namespaces that do not have a specific handler.
          Example::
  
              @socketio.on_error_default
              def error_handler(e):
                  print('An error has occurred: ' + str(e))
          """
          if not callable(exception_handler):
              raise ValueError('exception_handler must be callable')
          self.default_exception_handler = exception_handler
          return exception_handler