public function filter($string, $filter = null)
    {
        if (!isset($filter)) {
            $filter = $this->current_filter;
        }

        $delimiter = $this->config('teaser_delimiter', '<!--teaser-->');
        $string = str_replace($delimiter, htmlspecialchars($delimiter), $string);
        return $this->filter->run($string, $filter);
    }