usefor-article-09 February 2003

5.4.  Subject

   The Subject-header contains a short string identifying the topic of
   the message. This is an inheritable header (4.2.5.2) to be copied
   into the Subject-header of any followup, in which case the new
   Subject-content SHOULD then default to the string "Re: " (a "back
   reference") followed by the contents of the pure-subject of the
   precursor. Any leading "Re: " in that pure-subject MUST be stripped.

      header              =/ Subject-header
      Subject-header      = "Subject" ":" SP Subject-content
      Subject-content     = [ [FWS] back-reference ] pure-subject
      pure-subject        = unstructured
      back-reference      = %x52.65.3A.20
                          ; which is a case-sensitive "Re: "
   The pure-subject MUST NOT begin with "Re: ".

        NOTE: The syntax of unstructured differs from that prescribed in
        [RFC 2822], so ensuring that the Subject-content is not
        permitted to be completely empty, or to consist of WSP only (see
        remarks in 4.2.6 concerning undesirable headers).

   Followup agents MAY remove strings that are known to be used
   erroneously as back-reference (such as "Re(2): ", "Re:", "RE: ", or
   "Sv: ") from the Subject-content when composing the subject of a
   followup, and add a correct back-reference in front of the result.

        NOTE: that would be "SHOULD remove instances" except that we
        cannot find a sufficiently robust and simple algorithm to do the
        necessary natural language processing.

   Followup agents MUST NOT use any other string except "Re: " as a back
   reference. Specifically, a translation of "Re: " into a local
   language or usage MUST NOT be used.

        NOTE: "Re" is an abbreviation for the Latin "In re", meaning "in
        the matter of", and not an abbreviation of "Reference" as is
        sometimes erroneously supposed.

   Agents SHOULD NOT depend on nor enforce the use of back references by
   followup agents.

   For compatibility with legacy news software, the Subject-content of a
   control message (i.e. an article that also contains a Control-header)
   MAY start with the string "cmsg ", and non-control messages MUST NOT
   start with the string "cmsg ". See also section 6.13.

--- ../usefor-article-08/Subject.out          August 2002
+++ ../usefor-article-09/Subject.out          February 2003
@@ -13,7 +13,6 @@
       pure-subject        = unstructured
       back-reference      = %x52.65.3A.20
                           ; which is a case-sensitive "Re: "
-
    The pure-subject MUST NOT begin with "Re: ".
 
         NOTE: The syntax of unstructured differs from that prescribed in