usefor-article-03 February 2000

4.2.2.1.  Experimental Headers

   Experimental headers are those whose header-names begin with "X-".
   They are to be used for experimental Netnews features, or for
   enabling additional material to be propagated with an article. There
   are no established headers that are considered experimental headers;
   an established header cannot be experimental.
        NOTE: Some such headers may eventually be adopted as standard by
        some extension to this standard, at which point they will lose
        their "X-" prefix.