code: public function set($name, $value)
      {
          HttpSession::start();
  
          if (!preg_match("/^[\_a-z]/i", $name)) {
              throw new HttpException("Invalid session attribute: $name");
          }
  
          $_SESSION[$name] = $value;
      }
docs: Sets a request attribute.
  
  @param string $name  Request attribute.
  @param mixed  $value Request value.
  
  @return void