Dear folks,

The attached patch includes a change for adding a custom variable to easily
extend link grabbing capabilities for masOS user. When someone wants to add
an additional menu to call an external application, it will be possible by
adding a setting to the proposed variable as follows:

#+BEGIN_SRC emacs-lisp
(add-to-list 'org-mac-link-descriptors
               `("P" "apers" org-mac-papers-insert-frontmost-paper-link
,org-mac-grab-Papers-app-p) t)
#+END_SRC

This example intends to handle Papers.app, not freeware[*1], in macOS. If
`org-mac-papers-insert-frontmost-paper-link' and `mac-grab-Papers-app-p'
are implemented by user correctly, an appropriate link will be inserted
into an org buffer. I don't want put such codes to `org-mac-link.el'
directly to avoid unnecessary increase of file size. This scenario can be
applied to other applications.

The inserted link can be opened by `C-c C-o' if the corresponding link type
is configured by `org-link-set-parameters' like the following.

#+BEGIN_SRC emacs-lisp
(org-link-set-parameters
       "papers3"
       :follow (lambda (path)
                 (let ((cmd (concat "open papers3:" path)))
                   (shell-command-to-string cmd)
                   (message "%s" cmd))))
#+END_SRC

===================================================
* contrib/lisp/org-mac-link.el: Add a custom list for link descriptors

`org-mac-link-descriptors' is added to extend link grabbing capabilities.

Modified from a patch proposal by Takaaki Ishikawa.
===================================================

Kind regards,
Takaaki

[*1] http://papersapp.com/mac/

--
Takaaki ISHIKAWA <takaxp@ieee.org>