INT 21 U - DOS 4+ internal - DETERMINE IF CHARACTER REPRESENTS YES/NO RESPONSE
AX = 6523h
DL = character
DH = second character of double-byte character (if applicable)
Return: CF set on error
CF clear if successful
AX = type
00h no
01h yes
02h neither yes nor no


216523 - DOS 4+ internal - DETERMINE IF CHARACTER REPRESENTS YES/NO RESPONSE