Add "ITEM" to special properties

* lisp/org.el (org-special-properties): Add "ITEM".  Tiny fix to
  docstring.
(org-entry-properties): Compute "ITEM" property's value.
(org-buffer-property-keys): Remove hack since "ITEM" now officially
belongs to the special properties list.

* doc/org.texi (Special properties): Document "ITEM" change.

* testing/lisp/test-org.el (test-org/entry-properties): Add test.

doc/org.texi

@@ -5362,7 +5362,7 @@ CLOCKSUM_T   @r{The sum of CLOCK intervals in the subtree for today.}
 CLOSED       @r{When was this entry closed?}
 DEADLINE     @r{The deadline time string, without the angular brackets.}
 FILE         @r{The filename the entry is located in.}
-ITEM         @r{The headline of the entry.}
+ITEM         @r{The headline of the entry, with stars.}
 PRIORITY     @r{The priority of the entry, a string with a single letter.}
 SCHEDULED    @r{The scheduling timestamp, without the angular brackets.}
 TAGS         @r{The tags defined directly in the headline.}

lisp/org.el

@@ -15379,9 +15379,9 @@ a *different* entry, you cannot use these techniques."
 ;;; Properties API
 
 (defconst org-special-properties
-  '("TODO" "TAGS" "ALLTAGS" "DEADLINE" "SCHEDULED" "CLOSED" "PRIORITY"
-    "TIMESTAMP" "TIMESTAMP_IA" "BLOCKED" "FILE" "CLOCKSUM" "CLOCKSUM_T")
-  "The special properties valid in Org-mode.
+  '("ALLTAGS" "BLOCKED" "CLOCKSUM" "CLOCKSUM_T" "CLOSED" "DEADLINE" "FILE"
+    "ITEM" "PRIORITY" "SCHEDULED" "TAGS" "TIMESTAMP" "TIMESTAMP_IA" "TODO")
+  "The special properties valid in Org mode.
 These are properties that are not defined in the property drawer,
 but in some other way.")
 
@@ -15560,6 +15560,16 @@ strings."
 			       (/ (float clocksumt) 60.) 'add_times))
 			props)))
 	      (when specific (throw 'exit props)))
+	    (when (or (not specific) (string= specific "ITEM"))
+	      (when (looking-at org-complex-heading-regexp)
+		(push (cons "ITEM"
+			    (concat
+			     (org-match-string-no-properties 1)
+			     (let ((title (org-match-string-no-properties 4)))
+			       (when (org-string-nw-p title)
+				 (concat " " (org-remove-tabs title))))))
+		      props))
+	      (when specific (throw 'exit props)))
 	    (when (or (not specific) (string= specific "TODO"))
 	      (when (and (looking-at org-todo-line-regexp) (match-end 2))
 		(push (cons "TODO" (org-match-string-no-properties 2)) props))
@@ -16014,8 +16024,7 @@ COLUMN formats in the current buffer."
 	       (while (string-match "%[0-9]*\\(\\S-+\\)" value start)
 		 (setq start (match-end 0))
 		 (let ((p (org-match-string-no-properties 1 value)))
-		   (unless (member-ignore-case
-			    p (cons "ITEM" org-special-properties))
+		   (unless (member-ignore-case p org-special-properties)
 		     (add-to-list 'props p))))))))))
     (sort props (lambda (a b) (string< (upcase a) (upcase b))))))
 

testing/lisp/test-org.el

@@ -2475,6 +2475,11 @@ Text.
 
 (ert-deftest test-org/entry-properties ()
   "Test `org-entry-properties' specifications."
+  ;; Get "ITEM" property.
+  (should
+   (equal "* H"
+	  (org-test-with-temp-text "* TODO H"
+	    (cdr (assoc "ITEM" (org-entry-properties nil "ITEM"))))))
   ;; Get "TODO" property.
   (should
    (equal "TODO"