Re: An observation on draft-leiba-rfc2119-update-01

Stewart Bryant <> Tue, 07 February 2017 16:10 UTC

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Subject: Re: An observation on draft-leiba-rfc2119-update-01
To: Barry Leiba <>
References: <> <>
From: Stewart Bryant <>
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Date: Tue, 7 Feb 2017 16:10:23 +0000
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On 07/02/2017 15:45, Barry Leiba wrote:
> Hi, Stewart.
>> The above text raises an interesting problem. If the update system works
>> then
>> the text should read [RFC2119]. If the update system does not work than
>> the text needs to be [RFC2119],[RFCxxxx] as shown, but we also need to move
>> to a system where we always list the update set at the time of publication,
> It took me a while to get what you mean here, but I think I have it:
> you're saying that because this document (RFC xxxx) UPDATES RFC 2119,
> *any* document that cites RFC 2119 and is published after this one
> must automatically be taken to refer to this one and must follow the
> terms of this one.  So why have the double citation?
> You're right, as far as that goes, but if it's important to know for
> sure whether a document is following the terms of RFC xxxx or not (and
> see below about that), then I think it's important to be explicit
> about it.  It's a question of clarity: the reader of another document
> should not have to wonder, should not have to check publication dates,
> should not be uncertain.  Having the citation there explicitly is good
> for clarity.
> In fact, we *do* often (though not always) cite update documents when
> we're explicitly talking about a feature that was updated.  I think we
> do it when calling the reader's attention to the update is
> particularly important.

I am afraid I disagree. Either the update system works or it does not. 
If you think
people do not follow through the updates, then we need to always include 
list, or we need a system that always gives them the update when they 
request the
base document. So for example someone asking for RFC2119 would find this
automatically but distinctly appended to it.

Ironically in this case the result is no text change to the document 
making the
reference since a MUST is a MUST.

> Now, as to the other point:
>> I am also somewhat curious about the practical implication of
>> misinterpreting
>> MUST as must, and must as MUST.
>> For example: if A receives a foo packet, it MUST/must reply with a bar
>> packet
>> The interoperability considerations are identical, with but with the
>> advantage
>> that  MUST draws the eye of the reader to  the point and reducing the chance
>> that they will miss it. Similarly with the other keywords. So is there
>> really
>> a problem to be fixed here?
> This did come up in earlier discussion about "MUST".  Sure, it's
> possible that there really isn't a reason to define "MUST" in BCP 14
> because the English meaning is clear enough.  But "SHOULD" and "MAY"
> do need these definitions: the English meanings don't accurately
> convey the BCP 14 meaning.  And even with "MUST", the BCP 14 meaning
> explicitly says that it's a protocol requirement that affects
> interoperability or security, and we do seem to think that making that
> distinction is important.
> In any case, the current BCP 14 defines "MUST", and it's specifically
> not a goal of this document to change that older decision.

No, the point is that either type of must is exactly the same 
instruction - "do it or it's broken".

Similarly when should is given it is advisory, and there is no forcing 
how seriously the
individual takes that advice.

So if someone mistakes a MUST for a must, I don't see how the on the 
wire behaviour
can possibly change. Same for the other key words.

- Stewart

> Barry