I still think it's reasonably bogus to *present* this header as
"type/sub-type", when all it really contains is "format" (apparently, if
I send a bitmap as PostScript it has to be tagged with "Content-type:
TEXT-PLUS / POSTSCRIPT", giving my termcap-based mail-reader an
unreasonable expectation of being able to make something of it), but
getting the format through is the important thing. It's still a shame
that the document class can't be sent as well. But effective
compromises are rare enough to be worth preserving.