Client-side events are driven by the browser in response to user interaction with the page, for example, hover and mouseover events.
Client-side event handlers can be written to respond to these types of events. These event handlers are written in JavaScript in the 
HTML Element Properties of a Control.
The 
Client Event Map shows all the event handlers currently configured on your 
Page, usually you'll find it underneath the Entities tree or by choosing Show/Hide Client Event Map from the View menu.
The HTML Element Properties can be accessed by:
- Right-clicking a Control and selecting HTML Element Properties.
- Selecting a Control and pressing Ctrl + H.
- Clicking the
button on the HTML Element Properties property of a Control.
- Double-clicking on an event in the Client Event Map.
In these handlers you can reference JavaScript libraries that you've added to your Web Resources and call server-side functions using the Client-Server API.