Re: [salud] Section 13

Paul Kyzivat <pkyzivat@alum.mit.edu> Fri, 09 May 2014 00:09 UTC

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Subject: Re: [salud] Section 13
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On 5/8/14 4:13 PM, Dale R. Worley wrote:
> [as an author]
>
> Acting on Ben Campbell's suggestion that we consider revising the
> first sentence of section 13 so that it can support a MUST, I've
> written a revision:
>
> [In this message, I've separated the three sentences to make
> comparisons easier; it is all one paragraph.  I changed "explicitly
> instructed" to "instructed" in sentence 3.]
>
>       13.  User Agent Behaviour
>
>       The User Agent (UA) must produce a reasonable rendering
>       regardless of the combination of URIs (of any schemes) in the
>       Alert-Info header field:
>
>       It MUST produce a rendering based on the URIs that it can
>       understand and act on (if any), interpreted as prescribed by
>       local policy, and ignore the other URIs.
>
>       In particular, unless the containing message is a request and is
>       immediately rejected, the UA SHOULD provide some alert unless it
>       is instructed not to (for example, by Alert-Info URIs that it
>       understands, the presence of a Replaces or Joins header field,
>       local policy, or direction of the user).
>
> What do people think?
>
> I think that sentence 2 is really what we intended by sentence 1.  I
> left in sentence 1 to give guidance to the overall idea, while
> sentence 2 gives the details.

Sentence 3 is also needed. Sentence 2 doesn't cover the case where none 
of the URNs are understood.

	Thanks,
	Paul

> I included "URIs that it can ... act on", because it's possible that a
> UA could receive an http: URI but be unable to fetch its contents, or
> be unable to decode the fetched contents.
>
> Of course, sentence 2 allows a lot of latitude for implementations,
> because it says "interpreted as prescribed by local policy", but I
> think it gives the right effect, because, e.g., I don't think anyone
> is willing to say "local policy is that if we can't process a URI, we
> will just generate white noise".
>
> In sentence 3, I removed "explicitly" because a number of the listed
> factors that "instruct" the UA not to alert aren't really "explicit".
>
> And I found another cause not to alert:  re-INVITEs.  But I didn't add
> it to the list, because we already list 5 factors.  Presumably the
> implementors will understand that.
>
> However, I think that the fact that we've found another factor shows
> that we want this requirement to be a SHOULD.  As it says in RFC 2119:
>
>     3. SHOULD   This word, or the adjective "RECOMMENDED", mean that there
>     may exist valid reasons in particular circumstances to ignore a
>     particular item, but the full implications must be understood and
>     carefully weighed before choosing a different course.
>
> Dale
>
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