The only case I can see for this being as nonobvious and people seem to
think is that the requirements, although clearly stated, are scattered
throughout a set of very large documents. If that's the problem then the way
to fix it is to have a separate document that collects all of this stuff
and explains how to do these various sorts of transcodings. And hiding
that in the BINARYMIME specification isn't markedly more useful than
hiding it in the MIME specification itself.
if there are lots of details not already documented in published RFCs,
I agree that another document would be better. but I do think it would
be desirable to include a very brief discussion of transcoding issues
with references to published material, because folks who implement BINARYMIME
are likely to need to be concerned with those issues.
Keith