org-element: Allow multiple caption keywords

* lisp/org-element.el (org-element-multiple-keywords): Allow multiple
  caption keywords.
* contrib/lisp/org-export.el (org-export-get-caption): New function.
* testing/lisp/test-org-element.el: Add tests.
* testing/lisp/test-org-export.el: Add tests.

contrib/lisp/org-export.el

@@ -2900,6 +2900,19 @@ properties."
 		(read (format "(%s)" (mapconcat 'identity value " ")))))))
     (if property (plist-get attributes property) attributes)))
 
+(defun org-export-get-caption (element &optional shortp)
+  "Return caption from ELEMENT as a secondary string.
+
+When optional argument SHORTP is non-nil, return short caption,
+as a secondary string, instead.
+
+Caption lines are separated by a white space."
+  (let ((full-caption (org-element-property :caption element)) caption)
+    (dolist (line full-caption (cdr caption))
+      (let ((cap (funcall (if shortp 'cdr 'car) line)))
+	(when cap
+	  (setq caption (nconc caption (list " ") (copy-sequence cap))))))))
+
 
 ;;;; For Export Snippets
 ;;

lisp/org-element.el

@@ -248,8 +248,8 @@ Don't modify it, set `org-element-affiliated-keywords' instead.")
 The key is the old name and the value the new one.  The property
 holding their value will be named after the translated name.")
 
-(defconst org-element-multiple-keywords '("HEADER")
-  "List of affiliated keywords that can occur more that once in an element.
+(defconst org-element-multiple-keywords '("CAPTION" "HEADER")
+  "List of affiliated keywords that can occur more than once in an element.
 
 Their value will be consed into a list of strings, which will be
 returned as the value of the property.

testing/lisp/test-org-element.el

@@ -177,14 +177,20 @@ Some other text
   ;; Parse "parsed" keywords.
   (should
    (equal
-    '("caption")
+    '(("caption"))
     (org-test-with-temp-text "#+CAPTION: caption\nParagraph"
       (car (org-element-property :caption (org-element-at-point))))))
   ;; Parse dual keywords.
   (should
    (equal
-    '(("long") "short")
+    '((("long") "short"))
     (org-test-with-temp-text "#+CAPTION[short]: long\nParagraph"
+      (org-element-property :caption (org-element-at-point)))))
+  ;; Allow multiple caption keywords.
+  (should
+   (equal
+    '((("l1") "s1") (("l2") "s2"))
+    (org-test-with-temp-text "#+CAPTION[s1]: l1\n#+CAPTION[s2]: l2\nParagraph"
       (org-element-property :caption (org-element-at-point))))))
 
 
@@ -1688,14 +1694,21 @@ Outside list"
   (should
    (equal
     (org-element-interpret-data
-     '(org-data nil (paragraph (:caption ("caption")) "Paragraph")))
+     '(org-data nil (paragraph (:caption (("caption"))) "Paragraph")))
     "#+CAPTION: caption\nParagraph\n"))
   ;; Interpret dual keywords.
   (should
    (equal
     (org-element-interpret-data
-     '(org-data nil (paragraph (:caption (("long") "short")) "Paragraph")))
-    "#+CAPTION[short]: long\nParagraph\n")))
+     '(org-data nil (paragraph (:caption ((("long") "short"))) "Paragraph")))
+    "#+CAPTION[short]: long\nParagraph\n"))
+  ;; Interpret multiple parsed dual keywords.
+  (should
+   (equal
+    (org-element-interpret-data
+     '(org-data nil (paragraph
+		     (:caption ((("l1") "s1") (("l2") "s2"))) "Paragraph")))
+    "#+CAPTION[s1]: l1\n#+CAPTION[s2]: l2\nParagraph\n")))
 
 (ert-deftest test-org-element/center-block-interpreter ()
   "Test center block interpreter."

testing/lisp/test-org-export.el

@@ -479,6 +479,27 @@ body\n")))
     :attr_html
     (org-test-with-temp-text "Paragraph" (org-element-at-point)))))
 
+(ert-deftest test-org-export/get-caption ()
+  "Test `org-export-get-caption' specifications."
+  ;; Without optional argument, return long caption
+  (should
+   (equal
+    '("l")
+    (org-test-with-temp-text "#+CAPTION[s]: l\nPara"
+      (org-export-get-caption (org-element-at-point)))))
+  ;; With optional argument, return short caption.
+  (should
+   (equal
+    '("s")
+    (org-test-with-temp-text "#+CAPTION[s]: l\nPara"
+      (org-export-get-caption (org-element-at-point) t))))
+  ;; Multiple lines are separated by white spaces.
+  (should
+   (equal
+    '("a" " " "b")
+    (org-test-with-temp-text "#+CAPTION: a\n#+CAPTION: b\nPara"
+      (org-export-get-caption (org-element-at-point))))))
+
 
 
 ;;; Export Snippets