// restore noise to html content
        function restore_noise($text) {
            while (($pos=strpos($text, '___noise___'))!==false) {
                $key = '___noise___'.$text[$pos+11].$text[$pos+12].$text[$pos+13];
                if (isset($this->noise[$key]))
                    $text = substr($text, 0, $pos).$this->noise[$key].substr($text, $pos+14);
            }
            return $text;
        }