bug#33007: 27.0.50; Proposal for function to edit and return string

[Juri Linkov]

>> Additionally: we have enough room to include such instructions in the
>> buffer itself.  There are many keybindings for aborting in use (also in
>> third party packages) like C-c ESC, C-c C-k, C-c C-a.  And when you need
>> to know which one it was the message is long gone.  We could use the
>> header-line, or the mode-line, or the buffer header used when using the
>> :help-text key.
>
> Putting the instructions into a header line might be the nicest solution
> here...

This is exactly what org-src-mode does after invoking ‘C-c '’ 
(org-edit-special).
Its header-line-format is:

  "Edit, then exit with `\\[org-edit-src-exit]' or abort with 
`\\[org-edit-src-abort]'"