Locking a section of text in emacs

Today, I was talking to a friend about things that would be useful for text editors. One feature that we thought was missing was the ability to select a region of text, and lock it so as to prevent accidental editing without unlocking it.

This was rather trivial to add to emacs:

(defun lock ()
  "Make a section of text read-only, and add an overlay so 
   it's apparent"
  (interactive)
  (let ((start (region-beginning))
 (end (region-end)))
    (overlay-put (make-overlay start (+ 1 end)) 'face 
                 '(:background "light slate gray"))
    (put-text-property start end 'read-only t)))

(defun unlock ()
  "Unlock a region of text, and remove its overlay"
  (interactive)
  (let ((inhibit-read-only t)
 (start (region-beginning))
 (end (region-end)))
    (remove-overlays start (+ 1 end))
    (remove-text-properties start end '(read-only))))

Just bind lock and unlock to some keys, and there you go - makes a region of text uneditable, and adds an overlay to it.