8.3. Behaviors

The name behaviors won’t sound new to web developers experienced with programming in Internet Explorer. If you browse the documentation on the Microsoft Developer Network (MSDN) website, located at http://msdn.microsoft.com, you’ll find the following definition: “Element behaviors are encapsulated components, so they can add new and interesting functionality to a Web page while improving the organization of content, functionality, and style.”

Although the ASP.NET AJAX implementation is radically different—and cross-browser—the concept is much the same: You use behaviors to enhance the functionality of DOM elements. In this section, we’ll introduce client behaviors and explain how to create them. By the end, you’ll apply your new skills to create a behavior that uses CSS and the DOM to add client functionality to a text box element.