Bitfields for mouse call mask:
Bit(s)	Description	)
 0	call if mouse moves
 1	call if left button pressed
 2	call if left button released
 3	call if right button pressed
 4	call if right button released
 5	call if middle button pressed (Mouse Systems/Logitech/Genius mouse)
 6	call if middle button released (Mouse Systems/Logitech/Genius mouse)
 7-15	unused
Note:	some versions of the Microsoft documentation incorrectly state that CX
	  bit 0 means call if mouse cursor moves