I like to have the Help buffer in a some frame (with some other windows) and I try to reuse this window in this frame even when I am in another frame and issue a help command.
I tried setting
(setq display-buffer-alist
'(("\\*Help\\*" display-buffer-reuse-window)))
but this seem to reuse the window only when it is in the same frame.
How can I tell the display-buffer system to reuse a window in any (visisble) frame?
This is covered in the documentation for the function you're using.
Refer to all of the details regarding frames:
display-buffer-reuse-window is a byte-compiled Lisp function in
`window.el'.
(display-buffer-reuse-window BUFFER ALIST)
Return a window that is already displaying BUFFER.
Preferably use a window on the selected frame if such a window
exists. Return nil if no usable window is found.
ALIST is an association list of action symbols and values. See
Info node `(elisp) Buffer Display Action Alists' for details of
such alists.
If ALIST has a non-nil `inhibit-same-window' entry, the selected
window is not eligible for reuse.
If ALIST contains a `reusable-frames' entry, its value determines
which frames to search for a reusable window:
nil -- the selected frame (actually the last non-minibuffer frame)
A frame -- just that frame
`visible' -- all visible frames
0 -- all frames on the current terminal
t -- all frames.
If ALIST contains no `reusable-frames' entry, search just the
selected frame if `display-buffer-reuse-frames' and
`pop-up-frames' are both nil; search all frames on the current
terminal if either of those variables is non-nil.
If ALIST has a non-nil `inhibit-switch-frame' entry, then in the
event that a window on another frame is chosen, avoid raising
that frame.
This is an action function for buffer display, see Info
node `(elisp) Buffer Display Action Functions'. It should be
called only by `display-buffer' or a function directly or
indirectly called by the latter.
