[EMAIL PROTECTED] wrote:
1.
First, a complete nit: The title of section 6.2 is "UA Behavior to
Process 'multipart/alternative'", whereas it should be "UA Behavior to
Process 'multipart/related'".
2.
The handling of a multipart/mixed is 'required' if there is any
component whose handling is 'required'. (My previous message stated
this incorrectly.)
This has the sense that handling is a "global"
property, in that any part is marked 'required' if any simple part
within it is marked 'required'.
What are you looking at to draw the above conclusion?
I didn't have that impression. I figured it was "local" as you describe
below.
This rule causes various problems. One problem is that the parts of a
multipart/alternative are supposed to have handling 'optional'
(although the handling value is ignored), which requires that all
components of a part that is a component of a multipart/alternative
must be 'optional'. This makes it impossible to convey the logic of
the following example and similar situations (which are likely to
happen in practice):
This is an area that also bothers me. Perhaps the handling of parts of a
multipart/alternative are irrelevant, as they are for multipart/related,
unless the recipient doesn't understand and treats it as
multipart/mixed. Of course, if a multipart/alternative is processed as a
multipart/mixed the result isn't likely to be good.
X: multipart/alternative
|
| A: multipart/mixed: A1 is required, A2 and A3 are optional
| |
| | A1: simple
| |
| | A2: simple
| |
| | A3: simple
|
| B: multipart/mixed: B1 is required, B2 and B3 are optional
| |
| | B1: simple
| |
| | B2: simple
| |
| | B3: simple
That is, in order to process A correctly, A1 must be understood, and
similarly for processing B correctly. But the recipient only needs to
understand A *or* B.
Its my understanding that there is an assumption that the alternatives
are increasingly rich, and it is assumed that you do the last one you
understand, but that then you also understand all the prior ones. (So in
effect you the last one before the first one you don't understand,
rather than doing the last one you do understand.)
According to the current draft, A1 and B1 must be marked 'required',
which implies that A and B must be marked 'optional'. That
contradicts the rule for multipart/alternative, but worse, it doesn't
express the logic of the situation.
A better rule (IMHO) would be that the 'handling' value is 'local',
that is, it tells whether understanding the component is necessary for
understanding the part that contains it. Leaving the specification of
whether the containing part needs to be understood to the containing
part's handling value, and those of the parts that contain it.
This fix requires amending the draft by removing the prescription of
how the handling of a multipart/mixed part is determined by the
handling of its components. I believe that (within the specifications
and implications of the draft) the draft's processing logic is not
modified.
3.
A processor that does not implement multipart/related is allowed to
process the part as if it was multipart/mixed. It's not clear that
there are *any* circumstances under which this will result in useful
results. The current draft hints at this, but the hint should
probably be strengthened into a warning that multipart/related should
not be used in any circumstance where the recipient is not constrained
by some mechanism to implement multipart/related.
This seems reasonable to me.
I would think that someone building a multipart/related should construct
it such that something reasonable happens if it is processed as a
multipart/mixed. But certainly it may be impossible to do that.
Paul
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