docs: def _register_factory(self):
          """
          Index the available factories
  
          Query the plugins for an usable factory and register it
          """
          for name, info in self._plugins.items():
              if info['priority']:
                  factory = getattr(info['plugin'], 'factory', None)
                  if callable(factory):
                      registry[info['factory']] = info['plugin'].factory
          registry.freeze()