public function _extractLocations($words, $fulltext)
    {
        $locations = array();
        foreach ($words as $word) {
            $wordlen = strlen($word);
            $loc     = stripos($fulltext, $word);
            while ($loc !== false) {
                $locations[] = $loc;
                $loc         = stripos($fulltext, $word, $loc + $wordlen);
            }
        }
        $locations = array_unique($locations);
        sort($locations);

        return $locations;
    }