code: public static <CONTROLLER extends AbstractFXController> Pair<Pane, CONTROLLER> loadFxmlPaneAndControllerPair(final String fxmlFileUri, final Class<CONTROLLER> controllerClass, final Class clazz) throws CouldNotPerformException {
          return loadFxmlPaneAndControllerPair(fxmlFileUri, controllerClass, clazz, null);
      }
docs: Method load the pane and controller of the given fxml file.
  
  @param fxmlFileUri     the uri pointing to the fxml file within the classpath.
  @param controllerClass the class of the controller.
  @param clazz           the responsible class which is used for class path resolution.
  @param <CONTROLLER>    the type of controller which is controlling the new pane.
  
  @return an pair of the pane and its controller.
  
  @throws CouldNotPerformException is thrown if something went wrong like for example the fxml file does not exist.