usefor-article-06 November 2001

6.10.  References

   The References header lists optionally CFWS-separated message
   identifiers of precursors. The content syntax makes use of syntax
   defined in [RFC 2822].

      References-content  = msg-id *( CFWS msg-id )

        NOTE: This differs from the syntax of [RFC 2822] by requiring at
        least one CFWS between the msg-ids (this was an [RFC 1036]
        requirement).

   A followup MUST have a References header, and an article that is not
   a followup MUST NOT have a References header. In a followup, if the
   precursor did not have a References header, the followup's
   References-content MUST be formed by the message identifier of the
   precursor. A followup to an article which had a References header
   MUST have a References header containing the precursor's References-
   content (subject to trimming as described below) plus the precursor's
   message identifier appended to the end of the list (separated from it
   by CFWS).

   Followup agents SHOULD NOT trim message identifiers out of a
   References header unless the number of message identifiers exceeds
   21, at which time trimming SHOULD be done by removing sufficient
   identifiers starting with the second so as to bring the total down to
   21 (but the first message identifier MUST NOT be trimmed). However,
   it would be wrong to assume that References headers containing more
   than 21 message identifiers will not occur.

--- ../usefor-article-05/References.out          July 2001
+++ ../usefor-article-06/References.out          November 2001
@@ -24,6 +24,7 @@
    References header unless the number of message identifiers exceeds
    21, at which time trimming SHOULD be done by removing sufficient
    identifiers starting with the second so as to bring the total down to
-   21. However, it would be wrong to assume that References headers
-   containing more than 21 message identifiers will not occur.
+   21 (but the first message identifier MUST NOT be trimmed). However,
+   it would be wrong to assume that References headers containing more
+   than 21 message identifiers will not occur.