Filename
      Optional.  The name of the attachment.  You can use this to
      supply a recommended filename for the end‐user who is saving
      the attachment to disk.  You only need this if the filename at
      the end of the "Path" is inadequate, or if you’re using "Data"
      instead of "Path".  You should not put path information in here
      (e.g., no "/" or "\" or ":" characters should be used).

[...]

 Path
      Alternative to "Data" or "FH".  Path to a file containing the
      data... actually, it can be any open()able expression.  If it
      looks like a path, the last element will automatically be
      treated as the filename.  See "ReadNow" also.