docs: public String addExtent(Properties attributes) throws XDocletException
      {
          String name = attributes.getProperty(ATTRIBUTE_NAME);
  
          if (!_model.hasClass(name))
          {
              throw new XDocletException(Translator.getString(XDocletModulesOjbMessages.class,
                                         XDocletModulesOjbMessages.COULD_NOT_FIND_TYPE,
                                         new String[]{name}));
          }
          _curClassDef.addExtentClass(_model.getClass(name));
          return "";
      }