There are several ways to use HTML tags with XUL components in the same ZUML page. You can chose any of them based on your requirement.

First, you can use the html component to embed HTML tags. With this approach, the HTML tags are simply the content of the html component. They are sent to the client directly. They don't have any specify meaning to ZK.

Second, you can use the XHTML namespace (http://www.w3.org/1999/xhtml ) to specify a component from the XHTML component set. In othere words, the XHTML namespace denotes the associate XML element is a component from the XHTML component set. Like the ZUL component set (http://www.zkoss.org/2005/zul), ZK creates an instance for each XML element in a ZUML page.

Third, you can use the Native namespace ( http://www.zkoss.org/2005/zk/native) to represent a HTML tag that shall be sent directly to the client instead of creating a ZK component for each of them. When It is more efficient, but not dynamically changeable.

Last but not least, you can use inclusion (include) and inline frames (iframe) to embed another into a ZUL page with, theoretically, any kind of content (not limited to HTML tags