Описание тега web-controls
Web controls are classes that allow you to create Web server controls on a Web page
Web controls are classes that allow you to create Web server controls on a Web page. Web server controls run on the server and include form controls such as buttons and text boxes. They also include special-purpose controls such as a calendar. Because Web server controls run on the server, you can programmatically control these elements. Although Web server controls are rendered as HTML, their object model does not necessarily reflect HTML syntax.