INT 21 - DOS 2+ - "SWITCHAR" - GET SWITCH CHARACTER
AX = 3700h
Return: AL = status
00h successful
DL = current switch character
FFh unsupported subfunction
Desc:   Determine the character which is used to introduce command switches.
This setting is ignored by DOS commands in version 4.0 and higher,
but is honored by many third-party programs.
Notes:  documented in some OEM versions of some releases of DOS
supported by OS/2 compatibility box
always returns DL=2Fh for DOS 5.0

See also: 213701

213700 - DOS 2+ - "SWITCHAR" - GET SWITCH CHARACTER