--- a/tests/test-extension.t	Fri Mar 30 13:39:06 2018 -0700
+++ b/tests/test-extension.t	Fri Mar 30 12:16:46 2018 -0700
@@ -730,6 +730,10 @@
   called with a configurable set of options and two non-option arguments: paths
   to directories containing snapshots of files to compare.
   
+  If there is more than one file being compared and the "child" revision is the
+  working directory, any modifications made in the external diff program will be
+  copied back to the working directory from the temporary directory.
+  
   The extdiff extension also allows you to configure new diff commands, so you
   do not need to type 'hg extdiff -p kdiff3' always.