Such usage clearly violates RFC 2046 section 4.1.3, which states
that text/plain is intended for material that isn't formatted in any way:
Based on my reading of the RFC excerpt that Ned provided, I disagree,
for clearsigned messages. No interpretation is *necessary* for
proper display -- an agent can simply show the whole mess.
(The MIME charset header would apply, I presume.)
This sure sounds like sophistry to me.
And as it happens I'm the one who wrote this text. I can assure you that the
intent was to ban the use of text/plain for formatted materials. This was the
consensus at the time, and subsequent abuse of the type have if anything
strengthened the validity of this take on things.
Switching to yet another MIME multipart scheme won't help.
I never suggested any such thing. What I suggest was a different
subtype of text.