This page is intended for WW developer not for WW users. If your a user of WW hopefully you dont need to know these details, but certainly more knowledge is better, so if your hungry eat up!
The WW ajax/dhtml components use the DOJO Toolkit for both javascript event handling and AJAX calls.
To understand the widget framework this page is a must read:
http://dojotoolkit.org/docs/fast_widget_authoring.html
To understand the dojo event framework which is used extensively by the widget framework read this:
http://dojotoolkit.org/docs/dojo_event_system.html