private function getQualityFactor($locale, $option)
    {
        if (isset($option[1]))
            return (float) str_replace('q=', '', $option[1]);

        // Assign default low weight for generic values
        if ($locale === '*/*')
            return 0.01;

        if (substr($locale, -1) === '*')
            return 0.02;

        return null;
    }