diff -r 57c0d4888ca8 -r 7b5c8c8a2f8c mercurial/help/config.txt
--- a/mercurial/help/config.txt	Sat Jan 02 03:21:01 2016 -0800
+++ b/mercurial/help/config.txt	Sat Jan 02 03:11:52 2016 -0800
@@ -987,6 +987,19 @@
     Optional. Always use the proxy, even for localhost and any entries
     in ``http_proxy.no``. (default: False)
 
+``merge``
+---------
+
+This section specifies behavior during merges and updates.
+
+``checkunknown``
+   Controls behavior when an unknown file on disk has the same name as a tracked
+   file in the changeset being merged or updated to, and has different
+   contents. Options are ``abort``, ``warn`` and ``ignore``. With ``abort``,
+   abort on such files. With ``warn``, warn on such files and back them up as
+   .orig. With ``ignore``, don't print a warning and back them up as
+   .orig. (default: ``abort``)
+
 ``merge-patterns``
 ------------------