Date: Sat, 8 Feb 2014 08:59:31 -0800
From: "W. Trevor King" <wking@tremily.us>
To: David Bremner <david@tethera.net>
Subject: Re: [PATCH 2/2] emacs: Prefer Content-Description over filename for
	part buttons
Message-ID: <20140208165931.GB17142@odin.tremily.us>
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On Sat, Feb 08, 2014 at 08:55:02AM -0400, David Bremner wrote:
> "W. Trevor King" <wking@tremily.us> writes:
> > Rather than patching this in Emacs, maybe we should collapse the
> > =E2=80=9Cnot set=E2=80=9D and =E2=80=9Cset to empty string=E2=80=9D cas=
es in notmuch-show.c?  I
> > can't think of any reasons why someone would want to distinguish
> > those two cases, and it's easier all around if we standardize the
> > representation as far upstream as possible.
>=20
> Do the RFCs have anything to say about headers with empty content?
> If not I'd be inclined to leave the CLI output as raw as possible,
> just because people are always finding new ways to apply tools.

RFC 2183 does not describe Content-Description, it just uses it in
some examples [1].  In all the examples where Content-Description is
present, the value is not empty.  RFC 2045 defines
Content-Description, but it doesn't give all that much information
[2]:

  The ability to associate some descriptive information with a given
  body is often desirable.  For example, it may be useful to mark an
  "image" body as "a picture of the Space Shuttle Endeavor."  Such
  text may be placed in the Content-Description header field.  This
  header field is always optional.

    description :=3D "Content-Description" ":" *text

  The description is presumed to be given in the US-ASCII character
  set, although the mechanism specified in RFC 2047 may be used for
  non-US-ASCII Content-Description values.

I couldn't find more generic references to the meaning of empty header
values, but I find it hard to imagine anyone assigning semantic value
to an explicitly-empty description (vs. no Content-Description at
all).

Cheers,
Trevor

[1]: http://tools.ietf.org/html/rfc2183#section-3
[2]: http://tools.ietf.org/html/rfc2045#section-8

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