Dave Cridland wrote: > A SHOULD X unless Y essentially means "SHOULD (X or Y)" I'd read it as "do X, but if you have a very good excuse not doing X might do. One known very good excuse is Y." OTOH for a MUST X I'd want no qualifiers, MUST means "an attempt to do not X can cause havoc." This is also about a readability, I had a serious case of DEnglish some days ago, an article was tagged with a note: "This article may contain no original research". I read this as "apparently there is no original research in this article", which would be perfectly fine wrt the linked guideline. Only much later it occured to me that I got the "may ... not ..." wrong. If Y is the *only* possible very good excuse your version "MUST X or Y, SHOULD X" is clear. But SHOULD X often has an implicitly known very good excuse: Any older software written before the SHOULD X was approved. Frank _______________________________________________ IETF mailing list IETF@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf