Specifies that the drop-down control will be positioned relative to the owner control. This is usually beneath the owner control, but may also be above the control is there is insufficient space in which to show the entire drop-down control.
Specifies that the drop-down control will be positioned in the center of the application surface. This is especially useful for mobile applications where the browser viewport is limited in size.
The application surface is represented by the Surface property of the global Application variable in the WebForms unit.