code: public static <T extends Pane> CompletionStage<T> setContent(final T parent, final Node content) {
          return FxAsync.doOnFxThread(parent, parentNode -> {
              parentNode.getChildren().clear();
              parentNode.getChildren().add(content);
          });
      }
docs: Sets as the sole content of a pane another Node. This is supposed to work as having a first Pane being the wanted
  display zone and the second Node the displayed content.
  
  @param parent  The container defining the displayable zone, as a {@link Pane}.
  @param content The content to display
  @param <T>     The subtype if necessary of the container
  
  @return A {@link CompletionStage} to have monitoring over the state of the asynchronous operation