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     Any normal, system, or hidden file with a matching name will be
     opened by this function. If the file is read-only, the success of
     the operation also depends on the access code in bits 0-2 of
     register AL. After opening the file, the file read/write pointer
     is set to offset zero (the first byte of the file).
 
     The function fails if
 
        ■ Any element of the path name does not exist.
        ■ The file is opened with an access mode of read/write and the
          file has the read-only attribute.
        ■ [Version 3.0+] SHARE.EXE is loaded and the file has already been
          opened by one or more other processes in a sharing mode that
          is incompatible with the current program's request.
 
     The file's date and time stamp can be accessed after a successful
     open call with Int 21h Function 57h.
 
     The file's attributes (hidden, system, read-only, or archive) can
     be obtained with Int 21h Function 43h.
 
     When a file handle is inherited by a child process or is
     duplicated with Int 21h Functions 45h or 46h, all sharing and
     access restrictions are also inherited.
 
     [Version 3.0+]
     Bit 3 should always be zero; bits 4-7 control access to the file
     by other programs. Bits 4-6 have no effect unless SHARE.EXE is
     loaded.
 
     [Version 3.0+]
     A file-sharing error causes a critical-error exception (Int 24h)
     with an error code of 02h. Int 21h Function 59h can be used to
     obtain information about the sharing violation.
 
     [Version 4.0+]
     Int 21h Function 6Ch combines the services of Functions 3Ch, 3Dh,
     and 5Bh.
                                    -♦-