private static function _getPrefix($word)
    {
        $questionMarkPosition = strpos($word, '?');
        $astrericPosition     = strpos($word, '*');

        if ($questionMarkPosition !== false) {
            if ($astrericPosition !== false) {
                return substr($word, 0, min($questionMarkPosition, $astrericPosition));
            }

            return substr($word, 0, $questionMarkPosition);
        } else if ($astrericPosition !== false) {
            return substr($word, 0, $astrericPosition);
        }

        return $word;
    }