public function output($message, $depth = 0) {
        $samedepth = true;
        while ($this->currentdepth > $depth) {
            echo "</li>\n</ul>\n";
            $this->currentdepth -= 1;
            if ($this->currentdepth == $depth) {
                echo '<li>';
            }
            $samedepth = false;
        }
        while ($this->currentdepth < $depth) {
            echo "<ul>\n<li>";
            $this->currentdepth += 1;
            $samedepth = false;
        }
        if ($samedepth) {
            echo "</li>\n<li>";
        }
        echo htmlspecialchars($message);
        flush();
    }