OpenFile:

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   Open a file using a GUI if it is not specified.

   Since version 3.
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   Form:
   [fId, file, path] = OpenFile( path, file, suffix, heading, permission )
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   ------
   Inputs
   ------
   path       (1,:) Path to file
   file       (1,:) File name
   suffix     (1,:) Suffix (*.suffix) for the file
   heading    (1,:) Heading at top of dialog box
   permission (1,:) Permission. Default is r+

   -------
   Outputs
   -------
   fID        (1,1) File ID (-1 is failure)
   file       (1,:) File name
   path       (1,:) Path to file

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