From: Charles Lindsey (chl@clw.cs.man.ac.uk)
Date: Mon Jan 07 2002 - 11:46:42 CST
In <8GKTvwbHw-B@khms.westfalen.de> kaih@khms.westfalen.de (Kai Henningsen) writes:
>chl@clw.cs.man.ac.uk (Charles Lindsey) wrote on 01.01.02 in <Gp9KEF.4F8@clw.cs.man.ac.uk>:
>> Yes, but it is even worse than that. The X-header convention is not
>> mentioned at all! So, strictly speaking, any email with an X-header in it
>> is non-compliant. Even a header not defined in RFC 2822 is non-compliant
>> unless it is defined in some extension (e.g. in the MIME RFCs).
>Bull.
>Any not specifically mentioned field is an optional-field. That includes X-
>fields.
>And the reason those are not mentioned specifically is exactly the
>standardization problem. It was an explicit decision to drop the X-
>language because it did more harm than good.
OK. Point taken.
However, they may have gone too far.
Within Usenet, it seems that all the world and his dog likes to invent new
headers and put them into articles. We are not going to prevent that, but
we should try to keep some hold of the situation, and X-headers are a good
way to let everybody see that such a header is unofficial and can
(usually) be safely ignored. For the few genuine cases where some
sufficiently clued person is trying to make a useful extension to the
protocol, then maybe should be less rigorous. Anyway, here are some
wordings (with the originals) for you all to chew over:
In 4.2.1:
Header-names SHOULD be either those for which a USENET-header-content
is established by this standard, or by [RFC 2822], or by any
extension to either of these standards including, in particular, the
MIME standards [RFC 2045] et seq., or else experimental headers
beginning with "X-" (as defined in 4.2.2.1). Software SHOULD NOT
attempt to interpret headers not described in this standard or in its
extensions, but relaying agents MUST pass them on unaltered and
reading agents MUST enable them to be displayed, at least optionally.
[Alternative paragraph]
Whilst relaying agents MUST accept, and pass on unaltered, any non-
variant header whose header-name is syntactically correct, and
reading agents MUST enable them to be displayed, at least optionally,
posting and injecting agents SHOULD NOT generate headers other than
o those for which a USENET-header-content is established by this
standard or any extension to it,
o those recognised by other IESG-established standards, notably the
email standard [RFC 2822] and its extensions (including any IANA
registry of recognised headers that may be established in the
future),
o experimental headers beginning with "X-" (as defined in 4.2.2.1),
o on a provisional basis only, headers related to new protocols
under delevopment which are the subject of (or intended to be the
subect of) some IESG-approved RFC (whether Informational,
Experimental or Standards-Track).
However, software SHOULD NOT attempt to interpret headers not
specifically intended to be meaningful in the Netnews environment.
[End of alternative paragraph]
4.2.2.1. Experimental Headers
Experimental headers are those whose header-names begin with "X-".
They are to be used for experimental Netnews features, or for
enabling additional material to be propagated with an article. There
are no established headers (see 4.2.1) that are considered
experimental headers; an established header cannot be experimental.
NOTE: Some such headers may eventually be adopted as standard by
some extension to this standard, at which point they will lose
their "X-" prefix.
[Alternative paragraph]
Experimental headers are those whose header-names begin with "X-".
They are to be used for experimental Netnews features, or for
enabling additional material to be propagated with an article. They
are not (and will not be) defined by this, or any, standard.
NOTE: Experimental headers are suitable for situations where
they need only to be human readable. They are not intended to be
recognised by widely deployed Netnews software and, should such
a requirement be envisaged, it is preferable to use a normal
header on the provisional basis set out in section 4.2.1.
[End of alternative paragraph]
-- Charles H. Lindsey ---------At Home, doing my own thing------------------------ Tel: +44 161 436 6131 Fax: +44 161 436 6133 Web: http://www.cs.man.ac.uk/~chl Email: chl@clw.cs.man.ac.uk Snail: 5 Clerewood Ave, CHEADLE, SK8 3JU, U.K. PGP: 2C15F1A9 Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5