Private agreements about the meaning of mail messages can not be
prevented. A major aim of rfc-xxxx is to make them unnecessary. In
areas where it fails they will continue. In the first instance the
headers will be an area where private agreements continue but as Ned
has indicated this is not intended to be a permanent, or hopefully
even a long-lived, situation.
I'll just take this opportunity to repeat my 4 level model of what we
are doing. Something to think about while Ned and Nathaniel are slaving
away.
The 4 levels of communication in e-mail:
1. Mind to mind. We are trying to facilitate this but not standardize it.
2. Human experience level. At this level the message consists of
glyphs, pictures, sounds. We want to ensure that the receiver sees/hears
what the sender intends. And incidentally that the receiver is made
aware of any deficiencies in what is presented due to limitations
in his display equipment that the sender might not be aware of.
3. The underlying binary message. This is the message after all the
coding artifacts have been removed and just before it is presented to
the user. There should be a very clear and simple algorithmic correspondence
between levels 2 and 3.
4. An encoding of a whole message into a single sequence of octets (or
perhaps of bits) in such a way that the message is suitable for some
particular mechanism for transporting it. There needs to be a simple
and clear and deterministic algorithmic correspondence between the message
at this level and the message at level 3.
Some of the talk of a binary encoding suggests that people see it as
being identical with level 3. This is not true. At level 3 the message
is a structured object. A C++ class would be a good way to represent
it with lots of virtual functions to be made explicit in derived
classes corresponding to the various Content-types. I have started to
do this and it is a very thought-provoking exercise.
A binary encoding would still belong in level 4. It would include quite
a few arbitrary decisions about how it should be done. That is why it
shouldn't be in the initial rfc-xxxx but should be put in a separate
rfc if and when it is required.
We are trying to get to a situation where the mapping from 4->3->2 is
determined by the standard, not by private agreements. This will be
a major advance in electronic communication compared to the current
rough methods. We won't have got there while we still see a vertical
bar in a phrase when we display the From line of a message from Keld.
Bob Smart