Emacs: narrow-or-widen-dwim

gistfile1.el

(defun narrow-or-widen-dwim ()
  "If the buffer is narrowed, it widens. Otherwise, it narrows to region, or Org subtree."
  (interactive)
  (cond ((buffer-narrowed-p) (widen))
	((region-active-p) (narrow-to-region (region-beginning) (region-end)))
	((equal major-mode 'org-mode) (org-narrow-to-subtree))
	(t (error "Please select a region to narrow to"))))

;; I bind this key to C-c n, using the bind-key function that comes with use-package.
(bind-key "C-c n" 'narrow-or-widen-dwim)

;; I also bind it to C-x t n, using Artur Malabarba's toggle map idea:
;; http:://www.endlessparentheses.com/the-toggle-map-and-wizardry.html
(bind-key "n" 'narrow-or-widen-dwim toggle-map)

This is nice. Did you write this? If so, could I mention it on the blog?

Yes, and yes!

Nice. What I did though was add a speed command to org:
("n" . org-narrow-to-subtree)
but I still type M-x widen to undo it.