The See-Also header content lists message  IDs  of  articles
          that are related to this one but are not its precursors:

               See-Also-content = message-id *( space message-id )

See-Also resembles References, but without the restrictions imposed on References by the followup rules.

See-Also (あれも見よ。) は References (参照) に似ていますが、 References にある返信規則の制限はありません。

               NOTE: See-Also provides a  way  to  group  related
               articles,  such  as the parts of a single document
               that had to be split across multiple articles  due
               to  its size, or to cross-reference between paral-
               lel threads.

               NOTE: See the discussion (in section 6.5) on  MAIL
               compatibility issues of References and See-Also.

               NOTE:  In the specific case where it is desired to
               essentially make another article PART of the  cur-
               rent  one,  e.g. for annotation of the other arti-
               cle, MIME's "message/external-body" convention can
               be used to do so without actual inclusion.  "news-
               message-ID" was registered as a standard external-
               body  access method, with a mandatory NAME parame-
               ter giving the message ID  and  an  optional  SITE
               parameter  suggesting an NNTP site that might have
               the article available  (if  it  is  not  available
               locally), by IANA 22 June 1993.

               UNRESOLVED  ISSUE: Could the syntax be generalized
               to include URLs as alternatives  to  message  IDs?
               Here  it makes much more sense than in References.