The markup used to render the control at design time.
The System.Web.UI.Design.WebControls.BaseDataBoundControlDesigner class retrieves sample data that is used for binding purposes at design time before rendering the control. If the control is not data bound, it calls the BaseDataBoundControlDesigner.GetEmptyDesignTimeHtml method. If there is an error rendering the control, it calls the BaseDataBoundControlDesigner.GetErrorDesignTimeHtml(Exception) method.