code: private static function createBaseHelper($mode)
      {
          $isXhtml        = self::checkXhtmlFromMode($mode);
          $builder        = self::createBuilder($isXhtml);
          $emptyNodeNames = self::getEmptyNodeNames();
          return new BaseHelper($builder, $emptyNodeNames);
      }
docs: 指定されたモードに応じた BaseHelper を返します.
  
  @param  string $mode
  @return BaseHelper