code: public void addDrawer(JFXDrawer drawer) {
          if (drawer == null) {
              return;
          }
  
          if (drawer.getCachePolicy().equals(CachePolicy.IMAGE)) {
              throw new RuntimeException("Drawer is using unsupported cache strategy inside JFXDrawerStack");
          }
  
          if (drawers.isEmpty()) {
              if (content != null) {
                  drawer.setContent(content);
              }
          } else {
              drawer.setContent(drawers.get(drawers.size() - 1));
          }
  
          drawers.add(drawer);
          getChildren().setAll(drawer);
          drawer.setPickOnBounds(false);
  
          // add listener to bring drawer to front on hold
          JFXNodeUtils.addPressAndHoldHandler(drawer.sidePane, Duration.millis(300), event -> {
              if (drawers.indexOf(drawer) < drawers.size() - 1) {
                  drawer.bringToFront((param) -> {
                      updateDrawerPosition(drawer);
                      return param;
                  });
              }
docs: add JFXDrawer to the stack
  <p>
  NOTE: this method is also called inside {@link JFXDrawersStack#toggle(JFXDrawer)} to add
  the drawer if not added
  
  @param drawer