Re: SHOULD vs MUST

[Scott Brim <[e-mail]>]

On 6/25/08 5:37 AM, Fred Baker allegedly wrote:
> 
> On Jun 25, 2008, at 5:28 AM, Frank Ellermann 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."
> 
> That is more or less my definition of "should". I say something "must" 
> be so when I can tell you an operational failure that would or could 
> happen if it isn't. If I would like to say "must" but can think of a 
> case in which it would not be appropriate I say "should", and am saying 
> that if it is not so in someone's implementation they should be prepared 
> to say what their reason was.

... and draft authors should include explanations in their drafts of the 
reasons an implementor might legitimately have for not implementing the 
"should".  For example, an older operating system that does not support 
a new capability.
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