If you're an application developer
Though optional, you could have the total control of the client's functionality without the assistance of server-side code. Generally, you don't need to do it. You don't need to know how ZK Client Engine and client-side widgets communicate with the server. Their states are synchronized automatically by ZK and components. However, you could control it if necessary. It is the so-called Server-client fusion.
If you're a component developer
This section provides more detailed information about client-side programming, though it is written more for application developers. If you're not familiar with ZK's component development, please refer to ZK Component Development Essentials first.
In this section, we will discuss the details of the client-side control and programming.