--- a/mercurial/helptext/config.txt	Mon Dec 14 14:31:15 2020 +0100
+++ b/mercurial/helptext/config.txt	Mon Dec 14 18:09:37 2020 -0800
@@ -1521,12 +1521,13 @@
 
 ``premerge``
   Attempt to run internal non-interactive 3-way merge tool before
-  launching external tool.  Options are ``true``, ``false``, ``keep`` or
-  ``keep-merge3``. The ``keep`` option will leave markers in the file if the
-  premerge fails. The ``keep-merge3`` will do the same but include information
-  about the base of the merge in the marker (see internal :merge3 in
-  :hg:`help merge-tools`).
-  (default: True)
+  launching external tool.  Options are ``true``, ``false``, ``keep``,
+  ``keep-merge3``, or ``keep-mergediff`` (experimental). The ``keep`` option
+  will leave markers in the file if the premerge fails. The ``keep-merge3``
+  will do the same but include information about the base of the merge in the
+  marker (see internal :merge3 in :hg:`help merge-tools`). The
+  ``keep-mergediff`` option is similar but uses a different marker style
+  (see internal :merge3 in :hg:`help merge-tools`). (default: True)
 
 ``binary``
   This tool can merge binary files. (default: False, unless tool