From: Charles Lindsey (chl@clw.cs.man.ac.uk)
Date: Fri Dec 06 2002 - 11:54:15 CST
Here are the changes arising from Issue 3 (I have, of course, made the
necessary changes to the syntax, but will not bore you with them).
I have also included the replacement of 'other-parameter' by
'extension-parameter' together with revised wording as to when they
may be used, as discussed earlier. However, I have now allowed the
use of such parameters involving x-tokens, because I see that we
positively encourage their use (and rightly so) in the case of the
Injector-Info-header (but I might be persuaded that we should only allow
them where we explicitly say so, as in that case).
Old:
4.2.2. MIME-style Parameters
The possibility of allowing MIME-style parameters (whether header-
specific ones or generic extension-parameters) to appear in virtually
all headers is provided mainly for the purpose of allowing future
extensions to existing headers, since only a very few specific
parameters are defined in this standard. Observe that such parameters
do not, in general, occur in headers defined in other standards,
except for the MIME standards [RFC 2045] et seq. and their
extensions.
Other-parameters (whether those defined elsewhere or experimental
parameters whose attribute is an x-token) MAY be used, where the
syntax so allows, in any of the headers defined in this standard or
its extensions except that, at present, they SHOULD NOT be used in
headers in widespread use prior to the introduction of this standard
(this restriction is likely to be removed in a future version of this
standard). Nevertheless, compliant software MUST accept such
parameters where required by this standard (ignoring them if their
meaning is unknown) and SHOULD accept (and ignore) them in all
structured headers wherever defined.
NOTE: The syntax does not permit other-parameters in
unstructured headers (where they are unnecessary) or in certain
headers (notably the From-, Reply-To-, Mail-Copies-To- and
Complaints-To-headers) containing address-lists or mailbox-lists
(so that agents can simply replace the header-name by "To" or
"Cc" to obtain a header immediately suitable for sending Email,
and also so as to avoid some minor parsing problems with
<address>es).
New:
4.2.2. MIME-style Parameters
A few header-specific MIME-style parameters are defined in this
standard, but there is also provision for generic extension-
parameters to appear in most headers for the purpose of allowing
future extensions to those headers. Observe that such parameters do
not, in general, occur in headers defined in other standards, except
for the MIME standards [RFC 2045] et seq. and their extensions.
Extension-parameters, other than those using x-tokens, MUST NOT be
used unless they have first been defined in an IETF-approved RFC
(whether Informational, Experimental or Standards-Track) or, on a
provisional basis only, in relation to new protocols under
development which are the subject of (or intended to be the subject
of) some such IETF-approved RFC. They MUST ONLY be defined for use in
those headers where the syntax of this standard so allows. They
SHOULD NOT, at present, be defined for use in headers in widespread
use prior to the introduction of this standard (this restriction is
likely to be removed in a future version of this standard).
Nevertheless, compliant software MUST accept such parameters wherever
syntactically allowed in this standard (ignoring them if their
meaning is unknown) and SHOULD accept (and ignore) them in all
structured headers wherever defined.
[We could go further, and establish an IANA registry for these
parameters, preloaded with the ones already defined in this standard. A
good model for setting up such a registry is to be found in RFC 2183
(Content-Disposition).]
NOTE: The syntax does not permit extension-parameters in
unstructured headers (where they are unnecessary) or in certain
headers (notably the Date-, From-, Message-ID-, Reply-To-,
Sender-, Keywords-, Mail-Copies-To-, References-, Supersedes-
and Complaints-To-headers) which are the same (or similar to)
headers already existing in the Email standards.
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