The  Subject header's content (the "subject" of the article)
          is a short phrase describing the topic of the article:

               Subject-content  = [ "Re: " ] nonblank-text

          Encoded words MAY appear in this header.

          If the article is a followup, the subject SHOULD begin  with
          "Re: "  (a  "back reference").  If the article is not a fol-
          lowup, the subject MUST not begin  with  a  back  reference.
          Back references are case-insensitive, although "Re: " is the
          preferred form.  A followup  agent  assisting  a  poster  in
          preparing a followup SHOULD prepend a back reference, UNLESS
          the subject already begins with one.  If the  poster  deter-
          mines  that  the topic of the followup differs significantly
          from what is described in the subject, a new, more  descrip-
          tive,  subject  SHOULD  be  substituted (with no back refer-
          ence).  An article whose subject begins with a  back  refer-
          ence  MUST  have a References header referencing the precur-
          sor.

               NOTE: A back reference  is  FOUR  characters,  the
               fourth being a blank.  RFC 1036 was confused about
               this.  Observe also that only ONE  back  reference
               should be present.

               NOTE:  There  is a semi-standard convention, often
               used, in which a subject change is flagged by mak-
               ing the new Subject-content of the form:

                    new topic (was: old topic)

               possibly  with  "old  topic"  somewhat  truncated.
               Posters wishing to  do  something  like  this  are
               urged  to  use  this exact form, to simplify auto-
               mated analysis.

          For historical reasons, the  subject  MUST  not  begin  with
          "cmsg " (note that this sequence ends with a blank).

               NOTE:  Some  old  news  software  takes  a subject
               beginning with "cmsg " as an indication  that  the
               article is a control message (see sections 6.6 and
               7).  This mechanism is obsolete  and  undesirable,
               but accidental triggering of it is still possible.

          The subject SHOULD be terse.  Posters SHOULD avoid trying to
          cram  their  entire  article into the headers; even the sim-
          plest query usually benefits  from  a  sentence  or  two  of
          elaboration  and  context, and the details of header display
          vary widely among reading agents.

               NOTE: All-in-the-subject  articles  are  sometimes
               the  result of misunderstandings over the interac-
               tion protocol of a posting agent.  Posting  agents
               might wish to give special attention to the possi-
               bility that a poster specifying a very  long  sub-
               ject  might have thought he was typing the body of
               the article.