Answer the rectangle in which the list widget will pop-up. If possible, this is situated below the drop-down widget’s bottom side, but if the screen space there is not enough it could be above the drop-down widget’s above side. If there is no screen space above as well, we pick the side where we can offer the greatest number of lines in the pop-up widget.
Force the pop-up list widget to be visible.
Answer whether the pop-up widget is visible
Toggle the visibility of the pop-up widget.
Unmap the pop-up widget from the screen, transfer its selected item to the always visible text widget, and generate a callback.