The normal behavior is to set the diagram's selection collection to only those parts in the given rectangle r according to the Include policy. However, if the Shift key modifier was used, no parts are deselected -- this adds to the selection the parts in the rectangle not already selected. If the Control key modifier was used, this toggles the selectedness of the parts in the rectangle. If the Control key and Shift key modifiers were both used, this deselects the parts in the rectangle.