code: public void registerSnackbarContainer(Pane snackbarContainer) {
          if (snackbarContainer != null) {
              if (this.snackbarContainer != null) {
                  //since listeners are added the container should be properly registered/unregistered
                  throw new IllegalArgumentException("Snackbar Container already set");
              }
              this.snackbarContainer = snackbarContainer;
              this.snackbarContainer.getChildren().add(this);
              this.snackbarContainer.heightProperty().addListener(weakSizeListener);
              this.snackbarContainer.widthProperty().addListener(weakSizeListener);
          }
      }
docs: /////////////////////////////////////////////////////////////////////////