protected function add_extra_links($dom, $entry) {
        $link = $dom->createElement('link');
        $link->setAttribute('rel',  'enclosure');
        $link->setAttribute('href', portfolio_format_leap2a::get_file_directory() . $this->referencedfile->get_filename());
        $link->setAttribute('length', $this->referencedfile->get_filesize());
        $link->setAttribute('type', $this->referencedfile->get_mimetype());
        $entry->appendChild($link);
    }