public Explorer() {
   super(new DynamicNode(ROOT));
   PropertiesSet preferences = PropertiesManager.getPreferencePropertiesSet();
   if (preferences != null) {
     preferences.addPrefixPropertyChangeListener(
         DisplayToolTipsOptionGroup.class,
         DisplayToolTipsOptionGroup.TOOLTIPS_FIELD_VISIBILITY_PREFIX,
         new PreferencesListener());
     Db.addDbListener(dbslistener);
     tooltipsFields.addAll(Arrays.asList(DisplayToolTipsOptionGroup.getAvailableMetaFields()));
   }
 }