code: public function getExtra($name = null)
      {
          if ($name === null) {
              return $this->extra;
          }
          $arr = $this->extra;
          $bits = explode('.', $name);
          $last = array_pop($bits);
          foreach ($bits as $bit) {
              if (!isset($arr[$bit])) {
                  $arr[$bit] = [];
              }
              $arr = &$arr[$bit];
          }
          if (isset($arr[$last])) {
              return $arr[$last];
          }
          return null;
      }
docs: HELPER: