[XT] [AT]
Expects: AH    02H
Returns: AL    KbdShiftFlagsRec (status of Ctl, Alt, etc.)
Info: Returns the current status of the shift keys.  This is the same
as the byte at 0040:0017 in the BIOS Data Area.

Notes:   Additional shift-key information is available via INT 16H 12H
for systems equipped with 101-key BIOSes.

  There is no corresponding fn to set the keyboard shift status.

See Also: INT 16H (BIOS keyboard services)
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INT 16H 02H: Query Keyboard Shift Status