Small improvement of maintainability of link escaping

* lisp/org.el (org-link-escape-chars): Add comment with escape numbers
alphabetically ordered.
(org-link-escape-chars-browser): Add comment with escape numbers.
(org-link-escape): Use better readable char constant instead of number
constant for percent char.
(org-link-escape-browser): New function to substitute duplicate source
code.
(org-open-at-point): Substitute duplicate source code.
* testing/README: Make comment in source code example clearer.
* testing/lisp/test-org.el (test-org/org-link-escape-chars-browser):
Change URL to real use case and use the new function
`org-link-escape-browser'.

lisp/org.el

@@ -9732,11 +9732,13 @@ according to FMT (default from `org-email-link-description-format')."
 	  "]"))
 
 (defconst org-link-escape-chars
-  '(?\ ?\[ ?\] ?\; ?\= ?\+)
+  ;;%20 %2B %3B %3D %5B %5D
+  '(?\  ?\+ ?\; ?\= ?\[ ?\])
   "List of characters that should be escaped in link.
 This is the list that is used for internal purposes.")
 
 (defconst org-link-escape-chars-browser
+  ;;%20 %22
   '(?\  ?\")
   "List of escapes for characters that are problematic in links.
 This is the list that is used before handing over to the browser.")
@@ -9758,7 +9760,7 @@ If optional argument MERGE is set, merge TABLE into
   (mapconcat
    (lambda (char)
      (if (or (member char table)
-	     (and (or (< char 32) (= char 37) (> char 126))
+	     (and (or (< char 32) (= char ?\%) (> char 126))
 		  org-url-hexify-p))
 	 (mapconcat (lambda (sequence-element)
 		      (format "%%%.2X" sequence-element))
@@ -9767,6 +9769,13 @@ If optional argument MERGE is set, merge TABLE into
 			       (char-to-string char))) "")
        (char-to-string char))) text ""))
 
+(defun org-link-escape-browser (text)
+  (if (org-string-match-p
+       (concat "[[:nonascii:]" org-link-escape-chars-browser "]")
+       text)
+      (org-link-escape text org-link-escape-chars-browser)
+    text))
+
 (defun org-link-unescape (str)
   "Unhex hexified Unicode strings as returned from the JavaScript function
 encodeURIComponent.  E.g. `%C3%B6' is the german o-Umlaut."
@@ -10467,24 +10476,11 @@ application the system uses for this file type."
 	      (apply cmd (nreverse args1))))
 
 	   ((member type '("http" "https" "ftp" "news"))
-	    (browse-url
-	     (concat type ":"
-		     (if (org-string-match-p
-			  (concat "[[:nonascii:]"
-				  org-link-escape-chars-browser "]")
-			  path)
-			 (org-link-escape path org-link-escape-chars-browser)
-		       path))))
+	    (browse-url (concat type ":" (org-link-escape-browser path))))
 
 	   ((string= type "doi")
-	    (browse-url
-	     (concat org-doi-server-url
-		     (if (org-string-match-p
-			  (concat "[[:nonascii:]"
-				  org-link-escape-chars-browser "]")
-			  path)
-			 (org-link-escape path org-link-escape-chars-browser)
-		       path))))
+	    (browse-url (concat org-doi-server-url
+				(org-link-escape-browser path))))
 
 	   ((member type '("message"))
 	    (browse-url (concat type ":" path)))

testing/README

@@ -64,9 +64,9 @@ load and run the test suite with the following commands.
    Use this as a demo example of a failing test
    #+BEGIN_SRC emacs-lisp
      (ert-deftest test-org/org-link-escape-ascii-character-demo-of-fail ()
-       (should (string= "%5B"  ;; expected is right
+       (should (string= "%5B"  ;; expecting %5B is right
                         (org-link-escape "[")))
-       (should (string= "%5C"  ;; expected is wrong, "%5D" would be right
+       (should (string= "%5C"  ;; expecting %5C is wrong, %5D right
                         (org-link-escape "]"))))
    #+END_SRC
    or evaluate the ert-deftest form of the test you want to run.  Then

testing/lisp/test-org.el

@@ -524,9 +524,11 @@ http://article.gmane.org/gmane.emacs.orgmode/21459/"
   "Escape a URL to pass to `browse-url'."
   (should
    (string=
-    "http://some.host.com/search?q=%22Org%20mode%22"
-    (org-link-escape "http://some.host.com/search?q=\"Org mode\""
-		     org-link-escape-chars-browser))))
+    (concat "http://lists.gnu.org/archive/cgi-bin/namazu.cgi?query="
+	    "%22Release%208.2%22&idxname=emacs-orgmode")
+    (org-link-escape-browser
+     (concat "http://lists.gnu.org/archive/cgi-bin/namazu.cgi?query="
+	     "\"Release 8.2\"&idxname=emacs-orgmode")))))