usefor-article-04 April 2001

5.4.  Subject

   The Subject header contains a short string identifying the topic of
   the message. This is an inheritable header (4.2.2.2) to be copied
   into the Subject header of any followup, in which case the new
   header-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 the pure-subject MUST be stripped.

      Subject-content     = [ back-reference ] pure-subject
      pure-subject        = 1*( [FWS] utext )
      back-reference      = %x52.65.3A.20
                          ; which is a case-sensitive "Re: "

   The pure-subject MUST NOT begin with "Re: ".
        NOTE: The given syntax differs from that prescribed in [MESSFOR]
        insofar as it does not permit a header content to be completely
        empty, or to consist of WSP only (see remarks in 4.2.5
        concerning undesirable headers).

   Followup agents MAY remove instances of non-standard 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-03/Subject.out          February 2000
+++ ../usefor-article-04/Subject.out          April 2001
@@ -13,7 +13,6 @@
                           ; which is a case-sensitive "Re: "
 
    The pure-subject MUST NOT begin with "Re: ".
-
         NOTE: The given syntax differs from that prescribed in [MESSFOR]
         insofar as it does not permit a header content to be completely
         empty, or to consist of WSP only (see remarks in 4.2.5
@@ -27,6 +26,7 @@
         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.
@@ -40,5 +40,5 @@
    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 6.11.
+   section 6.13.