The theme-provider-class Element

[Default: none]

It specifies the class to provide the theme (aka., a style sheet file) URI dynamically. If you want to determine the theme based on the current user, cookie or locale. You can implement a class with the ThemeProvider interface, and specify it with the theme-provider-class element. Then, an instance of the class will be created, and it is called each time a desktop is rendered to the client to determine the theme URI.

Notice that the theme provider is called with all theme URIs that shall be generated (including what are specified in theme-uri and excluding what are specified in disable-theme-uri). And, only the return collection of URIs are actually generated. In other words, the theme provider has the highest priority.

For more information, please refer to ZK Developer's Reference.