Multipart/Alternate and TEXT/HTML in e-mail

Jacob Palme desires to be able to include alternates for Text/HTML
in email.  Examples have been proposed by Jacob and myself.  The
problem however lies with the mechanisms we have available,
Multipart/Alternate, Multipart/Related, and a flat subtype space.

To state the problem:  Multipart/Related requires a type
parameter which gives the type ot the object's root.  If the root
is Multipart/Alternative, then the MUA doesn't know what the type
is until after the Alternative is resolved.  If the
Multipart/Alternative incorporates two Multipart/Related entities
then the MUA must examine the type parameters to decide what to
do (effectively creating a subtype hierarchy).  Although I think
the latter approach is easier, I don't like either and I don't
know how to resolve the issue.

I've expressed Jacobs example both ways below.

Best.../Ed

Jacob's example:

1 Content-Type: Multipart/related
1.1   Content-Type: Multipart/alternative
1.1.1   Content-Type: Text/plain
        Content-Description: plain text version for those who
          cannot read HTML
1.1.2   Content-Type: Text/HTML
        Content-Description: HTML version of the same message,
          which many contain external file references,
          as shown in the example which follows on the next line

        <IMG SRC=HTTP://www.dsv.su.se/picture.GIF>
1.2   Content-Type: Image/GIF
      Content-Location: HTTP://www.dsv.su.se/picture.GIF
      Content-Description: the GIF picture

Reversing Releated and Alternative (using access-cid)

1 Content-type: Multipart/Alternative
1.1   Content-type: Multipart/Related; type=text/html
1.1.1   Content-Type: Text/plain
        Content-Description: plain text version for those who
          cannot read HTML
1.1.2   Content-Type: Message/External-body; access-type=content-id;

        Content-ID: <1(_dot_)3(_at_)accurate(_dot_)com>
        Content-type: Image/GIF
1.2   Content-type: Multipart/Related; type=text/plain
1.2.1   Content-Type: Text/HTML
        Content-Description: HTML version of the same message,
          which many contain external file references,
          as shown in the example which follows on the next line

        <IMG SRC=HTTP://www.dsv.su.se/picture.GIF>
1.2.2   Content-Type: Message/External-body; access-type=content-id;

        Content-ID: <1(_dot_)3(_at_)accurate(_dot_)com>
        Content-type: Image/GIF
1.3   Content-Type: Image/GIF
      Content-Location: HTTP://www.dsv.su.se/picture.GIF
      Content-Description: the GIF picture
      Content-ID: <1(_dot_)3(_at_)accurate(_dot_)com>