public static function addValue($key, $value, &$array, $glue = ' ')
    {
        if (isset($array[$key])) {
            if (!is_array($array[$key]))
                $array[$key] = explode($glue, $array[$key]);
            $array[$key][] = $value;
            $array[$key]   = array_unique($array[$key]);
            $array[$key]   = implode($glue, $array[$key]);
        } else
            $array[$key] = $value;
        return $array;
    }