For starters, the ASP.NET run time changes the client ID of your controls in the page. This is the id
attribute that is used in client script to access controls from JavaScript in the browser and with CSS
ID selectors. With normal ASPX pages, the server-side ID of a control is usually inserted one-on-one
in the final HTML. For example, a Button control with a server-side ID of Button1 in a normal
ASPX page defined with this code,