On an ASP.NET page, when controls are added declaratively between the opening and closing tags of a server control, ASP.NET automatically adds the controls to the containing server control's System.Web.UI.ControlCollection. Any HTML tags or text strings that are not processed on the server are treated as System.Web.UI.LiteralControl objects. These are added to the collection like other server controls.

The Control.Controls property allows you programmatic access to the instance of the System.Web.UI.ControlCollection class for any server control. You can add controls to the collection, remove controls from the collection, or iterate through the server controls in the collection.