+@vindex message-prune-recipient-rules
+@code{message-prune-recipient-rules} is used to prune the addresses
+used when doing a wide reply. It's meant to be used to remove
+duplicate addresses and the like. It's a list of lists, where the
+first element is a regexp to match the address to trigger the rule,
+and the second is a regexp that will be expanded based on the first,
+to match addresses to be pruned.
+
+It's complicated to explain, but it's easy to use.
+
+For instance, if you get an email from @samp{foo@@example.org}, but
+@samp{foo@@zot.example.org} is also in the @code{Cc} list, then your
+wide reply will go out to both these addresses, since they are unique.
+
+To avoid this, do something like the following:
+
+@lisp
+(setq message-prune-recipient-rules
+ '(("^\\([^@@]+\\)@@\\(.*\\)" "\\1@@.*[.]\\2")))
+@end lisp
+
+If, for instance, you want all wide replies that involve messages from
+@samp{cvs@@example.org} to go to that address, and nowhere else (i.e.,
+remove all other recipients if @samp{cvs@@example.org} is in the
+recipient list:
+
+@lisp
+(setq message-prune-recipient-rules
+ '(("cvs@@example.org" ".")))
+@end lisp
+