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  Function 29H (decimal 41) parses a string for a filename with the form
  DRIVE:FILENAME.EXT. Call this function with DS:SI pointing to a text
  string and ES:DI pointing to the drive-identifier byte in an unopened FCB.
  Function 29H attempts to extract the drive and filename information from
  the string, and to use it to initialize the drive and name fields of the
  FCB. If the function executes successfully, it returns AL = 00H if the
  string contains no wildcard characters or AL = 01H if the string contains
  at least one * or ? wildcard character. If the drive letter specifies an
  invalid drive, the function returns AL = FFH.

  Function 29H also updates DS:SI to point to the byte after the end of the
  filename in the string. This facilitates processing a string that contains
  multiple filenames. Also, if the parsing was unsuccessful, the FCB
  contains a blank filename.

  Function 29H lets you control four different aspects of the filename
  parsing. When you call the function, the 4 low-order bits of the value in
  AL specify how function 29H parses the string:

  .  If bit 0 is set, the function scans past separator characters (for
     example, leading blank spaces) to find the file specification. If bit 0
     is 0, the scan operation is not performed, and the file specification
     is expected to start in the first byte of the string.

  .  If bit 1 is set, then the drive byte in the FCB will be set only if it
     is specified in the file specification being scanned. This allows the
     FCB to specify a default drive.

  .  If bit 2 is set, the filename in the FCB is changed only if a valid
     filename is found in the string. This lets the FCB specify a default
     filename, which can be overridden by the filename in the string.

  .  If bit 3 is set, the filename extension in the FCB is changed only if a
     valid extension is found in the file specification. This allows the FCB
     to specify a default extension.

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  NOTE:
    Although this service can be handy, it is intended for use only with
    FCB-based file functions. You don't need this function if you rely on
    the handle-based file functions described in Chapter 17.
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