diff -r 94c0421d67a0 -r e928bedf0919 mercurial/help/config.txt
--- a/mercurial/help/config.txt	Thu Oct 25 00:22:42 2018 -0400
+++ b/mercurial/help/config.txt	Wed Oct 24 10:05:13 2018 -0400
@@ -2370,6 +2370,10 @@
     effect if ``HGPLAIN`` is set or ``HGPLAINEXCEPT`` is set and does
     not include ``tweakdefaults``. (default: False)
 
+    It currently means::
+
+      .. tweakdefaultsmarker
+
 ``username``
     The committer of a changeset created when running "commit".
     Typically a person's name and email address, e.g. ``Fred Widget