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        Parse filename (INT 21h, 29h)

        Entry:
          AH = 29h
          DS:SI = pointer to string to parse
          ES:DI = pointer to memory to fill with unopened FCB
          AL = bit mask to control parsing
                0 = 0: parsing stops if file separator found
                    1: leading separator ignored
                1 = 0: drive number in FCB set to default drive if not
                       present in string
                    1: drive number in FCB not changed
                2 = 0: filename in FCB set to blanks if no filename in
                       string
                    1: filename in FCB not changed if string does not
                       contain a filename
                3 = 0: extension in FCB set to blanks if no extension in
                       string
                    1: extension left unchanged
        Return:
          AL = 00: no wildcards in name or extension
               01: wildcards appeared
          DS:SI = pointer to first byte after parsed string
          ES:DI = unopened FCB

        Notes:  asterisks expanded to question marks in the FCB
                all processing stops when a filename terminator is
                encountered cannot be used with filespecs which include
                a path (DOS 2+)