> +1 to Brian and others saying upper case should be used sparingly, and > only where it really matters. If even then. That's the entire point: The terms provide additional information as to what the authors consider the important points of compliance to be. > The notion (that some have) that MUST means you have to do something > to be compliant and that a "must" (lower case) is optional is just > nuts. In some ways I find the use of SHOULD and SHOULD NOT be to be more useful than MUST and MUST NOT. MUST and MUST NOT are usually obvious. SHOULD and SHOULD NOT are things on the boundary, and how boundary cases are handled is often what separated a good implementation from a mediocre or even poor one. > If the ARP spec were to say, "upon receipt of an ARP request, the > recipient sends back an ARP response," does the lack of a MUST there > mean the response is optional? Surely not. And if we make it only a > SHOULD (e.g., to allow rate limiting of responses - a very reasonable > thing to do), does lack of MUST now make the feature optional from a > compliance/interoperability perspective? > The idea that upper case language can be used to identify all the > required parts of a specificition from a > compliance/conformance/interoperability perspective is just > wrong. This has never been the case (and would be exceeding painful to > do), though (again) some people seem to think this would be useful and > thus like lots of upper case language. At most it provides the basis for a compliance checklist. But such checklists never cover all the points involved in compliance. Heck, most specifications in toto don't do that. Some amount of common sense is always required. > Where you want to use MUST is where an implementation might be tempted > to take a short cut -- to the detriment of the Internet -- but could > do so without actually breaking interoperability. A good example is > with retransmissions and exponential backoff. You can implement those > incorrectly (or not at all), and still get "interoperability". I.e., > two machines can talk to each other. Maybe you don't get "good" > intereoperability and maybe not great performance under some > conditions, but you can still build an interoperabile implementation. > IMO, too many specs seriously overuse/misuse 2119 language, to the > detriment of readability, common sense, and reserving the terms to > bring attention to those cases where it really is important to > highlight an important point that may not be obvious to a casual > reader/implementor. Sadly true. Ned