INT 16 - KEYBOARD - GET SHIFT FLAGS
        AH = 02h
Return: AL = shift flags (see below)
SeeAlso: AH=12h,AH=22h,INT 17/AH=0Dh,INT 18/AH=02h

Bitfields for shift flags:
 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

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