ZK - Open Source Ajax Java Framework

hi all,
i'm looking for on how use multiple style in my zk project. i want use different color page, header an footer based on different user, then i search on zk theme.
i read that i can use theme provider, on documentation there is: "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."
but i don't understand how i use this feature. how can I specify name of other style? what parameter do i use to switch style in page? and where do i find more docs on this argument?
thank you
Vincenzo

maybe i expressed myself badly. no one know where do i find more documentation on theme provider?
tnx