The absense of such a statement is why I believe this to be
implementation-specific at the present time.
Oh, I'm happy to call it implementation-specific. I think what's
being described is a clear case of syntax violation, and I don't see
that it's a hard case or that syntax in an extension should be
different from syntax in the base spec in this regard. And I don't
look at it as being the same as doing MIME validation. But no matter;
it's not and important enough point to get stuck on.
In any case, I'm not suggesting changing the protocol definition.
Hannah asked for implementation advice, so I gave it. You can say
that that advice is specific to my implementation. :-)
By the way, the ABNF suggests that the number has to be given literally,
but the specification doesn't spell it out whether that really implies
the :importance parameter has to be a *constant* string in the sense of
the variables extension.
We thought it was clear that these were strings, which could be put in
as variables, but I see how it can be confusing. The intent is
certainly that variables may be used here. Perhaps we should enter an
erratum suggesting a comment in the ABNF that makes this clear.
I think that's a really bad idea because it puts us on the slippery slope of
specifying all the places where variables can be used. Unless we then go
through every specification and every parameter and add similar text will lead
people to the erroneous conclusion that variables can only be used in places
where the specifications say they can.
If this is in any way unclear - and I don't think it is - the place to explain
it better is in the variables specification. In fact as I recall the notion of
explicitly calling out all the placesa where variables can be used was
consideered during the development of that specifications and summarily
rejected.
I agree that it'd be better to put it into the variables spec. You
know I'm not suggesting going through everything to say where you can
and can't do variable substitution; you should know me better than
that. But Hannah has a point: the variables spec says this:
This extension changes the semantics of quoted-string, multi-line-
literal and multi-line-dotstuff found in [SIEVE] to enable the
inclusion of the value of variables.
...and the grammar for "importance" uses none of those three syntax
constructions. Taken at its word, that would imply that variable
substitution doesn't apply here. We might change RFC 5229 to add that
variables can substitute for literal strings as well. Or we might
decide that it's clear enough, and doesn't need changing.
Barry
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