code: public static void initClass() {
  
          // registers a factory for creating new instances of this widget
          CmsWidgetFactoryRegistry.instance().registerFactory(WIDGET_TYPE, new I_CmsFormWidgetFactory() {
  
              /**
               * @see org.opencms.gwt.client.ui.input.form.I_CmsFormWidgetFactory#createWidget(java.util.Map, com.google.common.base.Optional)
               */
              public I_CmsFormWidget createWidget(Map<String, String> widgetParams, Optional<String> defaultValue) {
  
                  Map<String, CmsPair<String, Boolean>> entries = new HashMap<String, CmsPair<String, Boolean>>();
                  String label = "Select";
                  if (widgetParams.containsKey("label")) {
                      label = widgetParams.get("label");
                      widgetParams.remove("label");
                  }
                  for (Map.Entry<String, String> entry : widgetParams.entrySet()) {
                      entries.put(entry.getKey(), CmsPair.create(entry.getValue(), Boolean.FALSE));
                  }
                  CmsMultiSelectCell cell = new CmsMultiSelectCell(entries);
                  cell.setOpenerText(label);
                  CmsMultiSelectBox box = new CmsMultiSelectBox();
                  box.addOption(cell);
                  return box;
              }
          });
      }
docs: Initializes this class.<p>