Macintosh
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Some discussion of Macintosh file type codes and their purpose can be
found in [MacOSFileTypes]. Additionally, please refrain from writing
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"none" or anything similar when no file extension or Macintosh file
type is specified, lest "none" be confused with an actual code value.
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... value "framed".
o A reference describing Macintosh Type codes has been added.
o Ietf-types ...