code: public void open() {
          if (!isAttached()) {
              RootPanel.get().add(this);
          }
          windowCount++;
          if(windowOverlay != null && !windowOverlay.isAttached()) {
              RootPanel.get().add(windowOverlay);
          }
  
          if (fullsceenOnMobile && Window.matchMedia(Resolution.ALL_MOBILE.asMediaQuery())) {
              setMaximize(true);
          }
  
          if (openAnimation == null) {
              getOpenMixin().setOn(true);
              OpenEvent.fire(this, true);
          } else {
              setOpacity(0);
              Scheduler.get().scheduleDeferred(() -> {
                  getOpenMixin().setOn(true);
                  openAnimation.animate(this, () -> OpenEvent.fire(this, true));
              });
          }
      }
docs: Open the window.