use="a-class-name"use="${EL_returns_a_class_or_a_class_name_or_a_component}"

It specifies a class to create a component instead of the default one. In the following example, MyWindow is used instead of the default class, org.zkoss.zul.html.Window.

<window use="MyWindow"/>

Notice that, if the expression returns a component, the component shall not belong to any page.