CI_User_agent::is_referral PHP Method

    public function is_referral()
    {
        if (!isset($this->referer)) {
            if (empty($_SERVER['HTTP_REFERER'])) {
                $this->referer = FALSE;
            } else {
                $referer_host = @parse_url($_SERVER['HTTP_REFERER'], PHP_URL_HOST);
                $own_host = parse_url(config_item('base_url'), PHP_URL_HOST);
                $this->referer = $referer_host && $referer_host !== $own_host;
            }
        }
        return $this->referer;
    }