Determining whether Emacs is in focus

[Aidan Gauland]

Hi,

Is there a way to find out if *any* Emacs frames are in focus in the
window manager?  I'm trying to set up notifications for ERC, but only
when Emacs is not in focus.  I haven't been able to find anything about
this in the manual—it seems that you can only find out which frame is
currently active—and apropos has turned up nothing relevant.  I asked in
#emacs on freenode: some people said they use window-manager-specific
hacks, and someone suggested looking at hoe
`cursor-in-non-selected-windows' is used, but the only occurrence of
that in the elisp files is for its definition, so I can only assume it
is used by the C part of Emacs.

So, can Emacs tell me itself, or do I have to resort to a
window-manager-specific hack?

Regards,
Aidan Gauland