CI_Session::_ci_load_classes PHP Method

    protected function _ci_load_classes($driver)
    {
        // PHP 5.4 compatibility
        interface_exists('SessionHandlerInterface', FALSE) or (require_once BASEPATH . 'libraries/Session/SessionHandlerInterface.php');
        $prefix = config_item('subclass_prefix');
        if (!class_exists('CI_Session_driver', FALSE)) {
            require_once file_exists(APPPATH . 'libraries/Session/Session_driver.php') ? APPPATH . 'libraries/Session/Session_driver.php' : BASEPATH . 'libraries/Session/Session_driver.php';
            if (file_exists($file_path = APPPATH . 'libraries/Session/' . $prefix . 'Session_driver.php')) {
                require_once $file_path;
            }
        }
        $class = 'Session_' . $driver . '_driver';
        // Allow custom drivers without the CI_ or MY_ prefix
        if (!class_exists($class, FALSE) && file_exists($file_path = APPPATH . 'libraries/Session/drivers/' . $class . '.php')) {
            require_once $file_path;
            if (class_exists($class, FALSE)) {
                return $class;
            }
        }
        if (!class_exists('CI_' . $class, FALSE)) {
            if (file_exists($file_path = APPPATH . 'libraries/Session/drivers/' . $class . '.php') or file_exists($file_path = BASEPATH . 'libraries/Session/drivers/' . $class . '.php')) {
                require_once $file_path;
            }
            if (!class_exists('CI_' . $class, FALSE) && !class_exists($class, FALSE)) {
                throw new UnexpectedValueException("Session: Configured driver '" . $driver . "' was not found. Aborting.");
            }
        }
        if (!class_exists($prefix . $class, FALSE) && file_exists($file_path = APPPATH . 'libraries/Session/drivers/' . $prefix . $class . '.php')) {
            require_once $file_path;
            if (class_exists($prefix . $class, FALSE)) {
                return $prefix . $class;
            } else {
                log_message('debug', 'Session: ' . $prefix . $class . ".php found but it doesn't declare class " . $prefix . $class . '.');
            }
        }
        return 'CI_' . $class;
    }