--- a/tests/test-help.t	Thu Dec 10 13:15:15 2020 -0500
+++ b/tests/test-help.t	Thu Dec 10 12:00:45 2020 -0800
@@ -642,13 +642,17 @@
          default to comparing against the working directory's first parent
          changeset if no revisions are specified.
   
-      When two revision arguments are given, then changes are shown between
-      those revisions. If only one revision is specified then that revision is
-      compared to the working directory, and, when no revisions are specified,
-      the working directory files are compared to its first parent.
+      By default, the working directory files are compared to its first parent.
+      To see the differences from another revision, use --from. To see the
+      difference to another revision, use --to. For example, 'hg diff --from .^'
+      will show the differences from the working copy's grandparent to the
+      working copy, 'hg diff --to .' will show the diff from the working copy to
+      its parent (i.e. the reverse of the default), and 'hg diff --from 1.0 --to
+      1.2' will show the diff between those two revisions.
   
       Alternatively you can specify -c/--change with a revision to see the
-      changes in that changeset relative to its first parent.
+      changes in that changeset relative to its first parent (i.e. 'hg diff -c
+      42' is equivalent to 'hg diff --from 42^ --to 42')
   
       Without the -a/--text option, diff will avoid generating diffs of files it
       detects as binary. With -a, diff will generate a diff anyway, probably