This document describes an extension to the int33 API to allow users to detect
if mouse interrupts come from a relative-input device (like a standard mouse)
or an absolute-input device (like a tablet, or an emulator like VirtualBox).

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Changes in the original INT 33h functions:

INT 33/000C - Define User Interrupt Routine
INT 33/0014 - Exchange User Interrupt Routines
Bitfields for mouse call mask:
Bit(s)	Description
 0-6	same as Table 03171 (as in int33.lst)
 7      (for vertical wheel movement -- seee wheelapi.txt)
 8      absolute mouse event
 9-15	unused
Notes:	when the user interrupt routine is called, bit 8 of CX indicates that
          the x, y coordinates passed in CX, DX come from an absolute pointing
          device (and therefore that the mickey counts in SI, DI may be zero or
          virtualized).
        bit 8 will not be set unless the user also sets bits 8 in the event mask
          passed to int33/000c or int33/0014. However, setting or clearing bit 8
          in the event mask shall have no other effect.