On Jan 7, 2013, at 4:53 AM, Stewart Bryant <stbryant@xxxxxxxxx> wrote: > Speaking as both a reviewer and an author, I would like > to ground this thread to some form of reality. > > Can anyone point to specific cases where absence or over > use of an RFC2119 key word caused an interoperability failure, > or excessive development time? I'm anecdotally familiar with some early pre-RFC 2543 SIP implementations where the implementors ignored everything that didn't say MUST and got something that didn't work. At all. But it was apparently really easy to develop, as the spec only had a few dozen MUST clauses, and the developers didn't include-by-reference any of the cited specs, such as SDP. When we were trying to decide whether to make RFC 3261 (the replacement of RFC 2543) a "draft standards" instead of a "proposed standard", I recall Robert Sparks and some others attempting to define a "fully interoperable implementation" test that tabulated all of the RFC 2119 invocations that had sprouted in FC 3261. They then immediately gave up the idea as impractical, we recycled at "proposed", and gave up on every making "full". The testing methodology has greatly improved since then, and it makes lithe use of RFC 2119 language for test definition or construction. -- Dean