Re: Is the "Subject" field of an e-mail an obvious example of "plain text" where no higher level protocol application is possible?

From: Martin J. Dürst <>
Date: Sat, 21 Jul 2012 15:10:01 +0900

Hello Karl,

On 2012/07/21 0:41, Karl Pentzlin wrote:
> Looking for an example of "plain text" which is obvious to anybody,
> it seems to me that the "Subject" field of e-mails is a good example.
> Common e-mail software lets you enter any text but gives you never
> access to any higher-level protocol. Possibly you can select the font
> in which the subject line is shown, but this is completely independent
> of the font your subject line is shown at the recipient.
> Thus, you transfer here plain text, and you can use exactly the
> characters which either Unicode provides to you, or which are PUA
> characters which you have agreed upon with the recipient before.
> In fact, the de-facto-standard regulating the e-mail content (RFC 2822,
> dated April 2001 , afaik)

No. If you go to, you'll see
Obsoleted by: 5322, Updated by: 5335, 5336.
RFC 5322 is the new version, date October 2008, but doesn't change much.
RFC 5335 and 5336 are experimental for encoding the Subject (and a lot
of other fields) as raw UTF-8 if the email infrastructure supports it.
There are Standards Track updates for these two, RFC 6531 and 6532.

But what's more important for your question, at least in theory, is, which defines a way to add language
information to header fields such as Subject:. With such information, it
would stop to be plain text.

In practice, RFC 2231 is not well known, and even less used, so except
for detailed technical discussion, your example should be good enough.

Regards, Martin.

> defines the content of the "Subject" line as "unstructured" (p.25),
> which means that is has to consist of US-ASCII characters, which in
> turn can denote other (e.g. Unicode) characters by the application of
> MIME protocols. Thus, the result is an unstructured character
> sequence.
> There is e.g. no possibility to include superscripted/subscripted
> characters in a "Subject" of an e-mail, unless these characters are
> in fact included as superscript/subscript characters in Unicode
> directly.
> Thus, proving the necessity to include a character in the text of a
> "Subject" line of an e-mail, is proving that the character has to be
> available as a plain text character. If, additionally, the character
> is used outside a closed group (which can be advised to use PUA
> characters), then there is a valid argument to include such a
> character in Unicode.
> Is my assumption correct?
> (I think of the SUBSCRIPT SOLIDUS proposed in WG2 N3980.
> It is in fact annoying that you cannot address DIN EN 13501
> requirements in an e-mail subject line written correctly,
> as Unicode, although being an industry standard, until now
> did not listen to an industry request at this special topic.)
> - Karl
Received on Sat Jul 21 2012 - 01:13:21 CDT

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