ned+ietf(_at_)mauve(_dot_)mrochek(_dot_)com wrote:
As always, the plural of anecdote is not data, so there may be places I'm
unaware of where this construct is in use and doesn't cause any problems.
...
Now, I suppose an argument could be made that this points to the need for
ADSP to specify semantics for handling multivalued From: fields in order not
to break multivalued From: even more. But that argument only makes sense if
we believe that there's a single semantic we can assign that is broadly
applicable, and I don't think anyone believes that.
This thread's taking place on the main IETF list, so it's probably worth noting
some deeper issues that your observations raise:
1. Should an adjunct protocol modify core semantics of the primary protocol,
rather than add semantics to it? If yes, when yes and when no?
The issue, in this particular case, is a challenge between waiting to
deprecate a feature in one protocol, versus potentially introducing
interoperability instabilities by failing to support that feature -- that is,
effectively deprecating it -- within a follow-on, adjunct protocol.
Cavalierly modifying core semantics creates incompatible variants, and
distributes their definition into unlikely places.
Since the likely answer to these sort of experience-generated questions is
usually "yes, but only sometimes", the real questions are when and how?
2. If a protocol has a features that remain unexercised for a long time, when
is it appropriate to deprecate it? To make the exercise a bit more challenging,
take note of situations in which the protocol is modeling well-established
behavior from elsewhere in the world, but which nonetheless is not a behavior
that has (yet) shown up in use of the protocol.
RFC5322 models the world of memos. Paper messages and other human
communications can be, and sometimes are, "from" multiple authors. That's not
just theory; it's real-world practice. If the Internet's email format drops
that construct from the only place in the message that provides a structured
designation of authorship, how are legitimate occurrences of multiple authors to
be indicated?
What we have here is a case of a protocol's supplying functional variety
that models the real-world, but which has remained virtually unused for 30
years. One can easily argue that the deeper "problem" is that Internet Mail
remains a limited functionality that will yet expand to fill the roles we know
-- from the paper world -- are yet needed. But even if we restrict the
historical review to the start of the mass market Internet (1994) we are still
looking at 15 years of not expanding into that available functionality. Failure
to use a feature for that long makes a strong case for deprecating it.
d/
--
Dave Crocker
Brandenburg InternetWorking
bbiw.net
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