left drag : up/down/left/right = image shift.
middle drag : left/right = zoom in/out (from centre)
up/down = rotate display about view direction.
right down : up/down = 3D rotation about vertical display axis.
left down and drag : Highlight current choice. left up : select curent choice and add to pick-list middle down : apply selected funtion to pick-list data right down : cancel pick-list