After porting XHMTL pages to ZK, you don't need to manipulate the DOM tree at the browser with JavaScript, though ZK doesn't prevent you from doing that. Rather, you manipulate XHTML components at the server, and then ZK engines updates the DOM tree at the browser for you.

It is convenient but there is a catch. ZK assumes the DOM tree at the browser is the same as the component tree at the server. In most cases, it is true. However, it is not always true.