1 files changed, 12 insertions, 0 deletions

diff --git a/lisp/simple.el b/lisp/simple.el
index db499b4f5a4..b3a0870ea4c 100644
--- a/lisp/simple.el
+++ b/lisp/simple.el
@@ -1289,6 +1289,18 @@ and it reactivates the mark."
     (set-mark (point))
     (goto-char omark)
     nil))
+
+(defun transient-mark-mode (arg)
+  "Toggle Transient Mark mode.
+With arg, turn Transient Mark mode on if and only if arg is positive.
+
+In Transient Mark mode, changing the buffer \"deactivates\" the mark.
+While the mark is active, the region is highlighted."
+  (interactive "P")
+  (setq transient-mark-mode
+        (if (null arg)
+            (not transient-mark-mode)
+          (> (prefix-numeric-value arg) 0))))
 
 (defvar next-line-add-newlines t
   "*If non-nil, `next-line' inserts newline to avoid `end of buffer' error.")