add_action('init', 'do_rewrite');
function do_rewrite(){
add_rewrite_rule( '^test/(.*)/?', 'index.php?page_id=5&sell_query_string=$matches[1]', 'top' );
add_rewrite_tag( '%sell_query_string%', '([^&]+)' );
}<html>
<body>
${require("path/to/header.html")}
</body>
</html>