code: private void startRootFor(final Stage stage, final Logger logger) {
      stage.actorProtocolFor(
          Stoppable.class,
          Definition.has(PrivateRootActor.class, Definition.NoParameters, PRIVATE_ROOT_NAME),
          null,
          addressFactory.from(PRIVATE_ROOT_ID, PRIVATE_ROOT_NAME),
          null,
          null,
          logger);
    }
docs: Starts the {@code PrivateRootActor}. When the {@code PrivateRootActor} starts it will in turn
  start the {@code PublicRootActor}.
  @param stage the {@code Stage} in which to start the {@code PrivateRootActor}
  @param logger the default {@code Logger} for this {@code World} and {@code Stage}