INT 62 u - FGDRIVER v3.03 - "FG_MUSICB" - PLAY SERIES OF NOTES IN BACKGROUND
        AX = 006Bh
        CX = number of repetitions (negative = continuous play)
        ES:BX -> '$'-terminated music string in BASIC PLAY format
Notes:  For FGDRIVER v1.10, this function was unused; "FG_MUSICB" was AX=008Dh
        This call is ignored if asynchronous sound (AX=0089h,AX=008Bh,
          AX=008Dh) is already in progress
SeeAlso: AX=0048h,AX=006Bh,AX=009Eh,AX=00ABh

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