docs: def set_default_reference(self, method, reference):
          """
          Set the default reference for a method.
  
          :arg method: name of a method
          :type method: :class:`str`
  
          {reference}
          """
          if method not in self._available_methods:
              raise ValueError('Unknown method: {0}'.format(method))
          self._default_references[method] = reference