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

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 http://www.ietf.org/rfc/rfc2822.txt , afaik)
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 Fri Jul 20 2012 - 10:49:57 CDT