INT 16 - KEYBOARD - GET EXTENDED SHIFT STATES (enh kbd support only)
        AH = 12h
Return: AL = shift flags 1 (same as returned by AH=02h) (see below)
        AH = shift flags 2 (see below)
Notes:  AL bit 3 set only for left Alt key on many machines
        AH bits 7 through 4 always clear on a Compaq SLT/286
        INT 16/AH=09h can be used to determine whether this function is
          supported, but only on later model PS/2s
SeeAlso: AH=02h,AH=09h,AH=22h,AH=51h,INT 17/AH=0Dh

Bitfields for shift flags 1:
 bit 7  Insert active
 bit 6  CapsLock active
 bit 5  NumLock active
 bit 4  ScrollLock active
 bit 3  Alt key pressed (either Alt on 101/102-key keyboards)
 bit 2  Ctrl key pressed (either Ctrl on 101/102-key keyboards)
 bit 1  left shift key pressed
 bit 0  right shift key pressed

Bitfields for shift flags 2:
 bit 7  SysRq key pressed
 bit 6  CapsLock pressed
 bit 5  NumLock pressed
 bit 4  ScrollLock pressed
 bit 3  right Alt key pressed
 bit 2  right Ctrl key pressed
 bit 1  left Alt key pressed
 bit 0  left Ctrl key pressed

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