@end smallexample
@c Emacs 19 feature
-If @var{oldmap} is non-@code{nil}, then its bindings determine which
-keys to rebind. The rebindings still happen in @var{keymap}, not in
-@var{oldmap}. Thus, you can change one map under the control of the
+If @var{oldmap} is non-@code{nil}, that changes the behavior of
+@code{substitute-key-definition}: the bindings in @var{oldmap} determine
+which keys to rebind. The rebindings still happen in @var{keymap}, not
+in @var{oldmap}. Thus, you can change one map under the control of the
bindings in another. For example,
@smallexample