Using the default binds.conf and changing the value of
[compose::editor] brings different results (found by using
emacs -nw as editor):
<C-x>brings the command prompt,
:is passed to emacs.
<C-x>is passed to emacs, but
:brings the command prompt when it shouldn't.
:is passed to emacs, but
<C-b>is also passed to emacs, when it should bring the prompt.
<Esc>: everything works as expected,
:is passed to emacs and
<Esc>does bring the command prompt.