code: public void mark() {
      // ensure it's not marked yet - so a control doesn't contain the same styleClass multiple times
      if (!marked) {
        preferencesGroup.getRenderer().addStyleClass(MARKED_STYLE_CLASS);
        preferencesGroup.getRenderer().getTitleLabel().setOnMouseExited(unmarker);
        marked = !marked;
      }
    }
docs: Marks this group in the GUI.
  Is used for the search, which marks and unmarks items depending on the match as a form of
  visual feedback.