This is functionality I'd like to add to rect.el. It allows you to specify a
rectangular region, and then edit just the contents of that rectangle in a
separate buffer. When finished (C-c C-c), it replaces the old rectangle using
insert-rectangle with the new contents.

I'd appreciate comments on usability, fitness, etc.

--8<---------------cut here---------------start------------->8---
(defvar edit-rectangle-origin)
(defvar edit-rectangle-saved-window-config)

(defun edit-rectangle (&optional start end)
  (interactive "r")
  (let ((strs (delete-extract-rectangle start end))
        (mode major-mode)
        (here (copy-marker (min (mark) (point)) t))
        (config (current-window-configuration)))
    (with-current-buffer (generate-new-buffer "*Rectangle*")
      (funcall mode)
      (set (make-local-variable 'edit-rectangle-origin) here)
      (set (make-local-variable 'edit-rectangle-saved-window-config) config)
      (local-set-key (kbd "C-c C-c") #'restore-rectangle)
      (mapc #'(lambda (x) (insert x ?\n)) strs)
      (goto-char (point-min))
      (pop-to-buffer (current-buffer)))))

(defun restore-rectangle ()
  (interactive)
  (let ((content (split-string (buffer-string) "\n"))
        (origin edit-rectangle-origin)
        (config edit-rectangle-saved-window-config))
    (with-current-buffer (marker-buffer origin)
      (goto-char origin)
      (insert-rectangle content))
    (kill-buffer (current-buffer))
    (set-window-configuration config)))
--8<---------------cut here---------------end--------------->8---

-- 
John Wiegley                  GPG fingerprint = 4710 CF98 AF9B 327B B80F
http://newartisans.com                          60E1 46C4 BD1A 7AC1 4BA2