Client events occurs on the client and is JavaScript. In general, developers do NOT need to write JavaScript. All required code is generated. But it is necessary to invoke some of the events as they might be used to open certain functionality. 


A special case if you want to implement Ajax events. Suppose you want to perform some action when a user clicks on a button, but you do not want to submit the data, but use an Ajax event.


The button has a server AND a client event of the same name (onClick). As the user clicks on the button an JavaScript event is required to send a message to the server. To invoke, you can click on the JavaScript event, that will add the event to the property editor and open the editor that contains the required code (no need to change). The PHP event can be created and the editor opens the PHP editor with a function prototype. That is where you can put your custom code.


Don't worry, during this course you will learn all about this.