code: protected final void notifyOnAreaShown(@NonNull final Area area) {
          for (AreaListener listener : areaListeners) {
              listener.onAreaShown(area);
          }
      }
docs: Notifies the listeners, which have been registered to be notified, when the visibility of the
  dialog's areas has been changed, about an area being shown.
  
  @param area
  The area, which has been shown, as a value of the enum {@link Area}. The area may not
  be null