Hi,

I use this to always display the *Help* buffer in the selected window,
or to reuse existing window displaying the same buffer:

  (add-to-list 'display-buffer-alist
               '("^\\*Help\\*$" . ((display-buffer-reuse-window
                                    display-buffer-same-window))))

With this, whenever I forget the keybindings available during
query-replace and hit '?' to get help, the help buffer is displayed in
the main window which shows the replacements to be performed.  When I
try to bury the help buffer with 'q', it doesn't do what I intended - it
quits the query-replace session.  The same thing happens when I try to
switch to the main window with 'C-x o' and manually kill the buffer.

The only thing that works really, is to enter recursive edit, kill the
help buffer and exit-recursive-edit.

This happens because the help buffer generated by perform-replace is
named "*Help*" and my display-buffer rule matches it.  I work around
this by adding an additional rule to display-buffer-alist which checks
if the help buffer was created by perform-replace.  It's ugly:

  (defun my//display-buffer-help-for-query-replace-condition (bufname action)
    (and (string-match-p "\\*Help\\*" bufname)
         (catch 'res
           (mapbacktrace (lambda (_evald func _args _flags)
                           (when (eq func 'perform-replace)
                             (throw 'res t)))))))
  (add-to-list 'display-buffer-alist
               '(my//display-buffer-help-for-query-replace-condition
                 . (display-buffer-pop-up-window)))


There are a couple of ways to improve behavior of perform-replace:

- Use a different name for the query-replace help buffer (patch attached)
- Make 'C-l' or some other key bury the help buffer, if it was displayed
  in the main window
- Make '?' toggle visibility of the help buffer
- Allow switching windows in query-replace
- Display the help message in the minibuffer