Zend_Config::readOnly PHP Method

    public function readOnly()
    {
        return !$this->_allowModifications;
    }

 /**
  * Sets the default route according to the configuration data provided in $config.
  * Two settings are required: the route prefix (key: routePrefix),
  * and the controller class-name (key: controllerClass).
  *
  * Three optional settings are supported as well: major section (key: majorSection),
  * minor section (key: minorSection) and request parameters (key: params);
  * which might be used during the routing process.
  *
  * @param Zend_Config $config Configuration data
  * @param array $dependencyData Data array supplied by the "init_dependencies" event
  * @throws XenForo_Exception
  */
 public static function setDefaultRoute(Zend_Config $config, array $dependencyData)
 {
     $routesPublic = $dependencyData['routesPublic'];
     if (!$config->routePrefix || !$config->controllerClass) {
         // Debugging message. No need for phrasing.
         throw new XenForo_Exception('Missing route-prefix and/or controller class-name.');
     }
     if ($config->readOnly()) {
         // A read-only object was passed. Arghh!
         $newConfig = new Zend_Config(array('routeClass' => $routesPublic[$config->routePrefix]['route_class']), true);
         $config = $newConfig->merge($config);
     } else {
         $config->routeClass = $routesPublic[$config->routePrefix]['route_class'];
     }
     self::_setCustomRoutePrefixes($config->routePrefix, $routesPublic);
     $config->setReadOnly();
     XenForo_Application::set('customIndex', $config);
 }