Re: Different (buffer-file-)coding-systems for different regions of one buffer? (for Rmail MIME)

[Richard Stallman]

    Otherwise, there are at least two radically different views of many
    files, and there must be a buffer (in the generic sense of a separate
    region of memory) for presentation, and one for the much more
    restricted changes you wish propagated back to the file (setting
    flags).  I see no good reason why the region of memory used for
    presentation shouldn't "waste" a few score bytes and be promoted to an
    Emacs buffer.

It pretty much has to be an Emacs buffer, or part of one.  There is no
other natural or easy way to implement it in the context of Emacs.
The question would be, is it a separate buffer, or a part of another
buffer, or what?

In Rmail currently it is possible to type e and edit a message.
Right now we do this through editing the buffer of the RMAIL file.
With better MIME support, this may have to be implemented differently,
but I hope we can keep it working somehow.

If we copy the message into another buffer for viewing, that tends to
lead to complications of the situation, because there are multiple
buffers instead of just one.  We could try adding features to hide
that, or we could expose it and not hide anything.