On Mon, Mar 07 2016, Jani Nikula wrote:
> For a message with mime structure:
>
> └┬╴multipart/mixed 120338 bytes
>  ├─╴text/html 59234 bytes
>  └─╴application/octet-stream attachment [filename.html] 59234 bytes

How is this displayed when viewing the message (as opposed to replying)?

How do you think that it is intended to be displayed? Are they two
sub-parts of the multipart/mixed intended to be alternatives? (It
doesn't seem so, as you mention later that they have the same content.)

> this patch (i.e. commit e103f0a971b8 emacs/mua: Generate improved cited
> text for replies) causes the application/octet-stream attachment to be
> displayed, with:
>
> [ filename.html: application/octet-stream (as text/html) ]
> !!! Bodypart insert error: Internal error: No :content from ("show" "--format=sexp" "--include-html" "--part=3" "--decrypt" "id:mid@example.com") !!!

If someone can give me a sample message then I will fix this.

> Is there a way to interactively choose which parts are cited in replies?

Currently, no.