Assembly: System.Web (in system.web.dll)
Use the Focus method to set the initial focus of the Web page to the control. The page will be opened in the browser with the control selected.
The Focus method causes a call to the page focus script to be emitted on the rendered page. If the page does not contain a control with an HTML ID attribute that matches the control that the Focus method was invoked on, then page focus will not be set. An example where this can occur is when you set the focus on a user control instead of setting the focus on a child control of the user control. In this scenario, you can use the FindControl method to find the child control of the user control and invoke its Focus method.