If you prefer to modify a static HTML page directly by adding the rich content, you could use the Native namespace (http://www.zkoss.org/2005/native) to specify the static content, and then use the XUL or XHTML component sets (http://www.zkoss.org/2005/zul and http://www.w3.org/1999/xhtml) for the content that are changed dynamically.
<!-- test.zhtml -->
<html xmlns="http://www.zkoss.org/2005/native" xmlns:h="http://www.w3.org/1999/xhtml" xmlns:z="http://www.zkoss.org/2005/zul">
<head>
<title>Hi ZK</title>
</head>
<body>
<h:ul id="list"><!-- dynamically changeable -->
<h:li><z:textbox/></h:li>
</h:ul>
<p>Static content</p>
</body>
</html>