quoted strings within quoted strings

This reflects a problem that has come up with a proposed feature in
USEFOR, but it arises out of the syntax of MIME.

Currently, various MIME headers (and some new USEFOR headers) can have
parameters of the form

        attribute = value
where
        attribute = token
        value = token / quoted-string

There is provision for new parameters to be defined in later standards,
and registered with IANA. Typically, the "values" involved are things like
charsets and filenames.

Now suppose someone invents a parameter where the "value" is to be a
mailbox (I don't think that case has arisen yet in MIME, but it well
might).  Perhaps something like:

        "sender" "=" mailbox

Obviously, the mailbox has to be a quoted-string (it contains an '@',
which is a tspecial). BUT a mailbox can itself contain a quoted-string in
many situations, so one might want to write

but, of course, you can't write that because it contains nested
quoted-strings.

So what is the proper way to do it?
Would it be

        sender = "\"John D. Bloggs\" <jdbloggs(_at_)example(_dot_)com>"

in which case would/should the inner \"John D. Bloggs\" then be
interpreted as a quoted-string?

Or is it the case that there is no proper way to express this sort of
thing?

-- 
Charles H. Lindsey ---------At Home, doing my own thing------------------------
Tel: +44 161 436 6131 Fax: +44 161 436 6133   Web: http://www.cs.man.ac.uk/~chl
Email: chl(_at_)clw(_dot_)cs(_dot_)man(_dot_)ac(_dot_)uk      Snail: 5 
Clerewood Ave, CHEADLE, SK8 3JU, U.K.
PGP: 2C15F1A9      Fingerprint: 73 6D C2 51 93 A0 01 E7 65 E8 64 7E 14 A4 AB A5