ox: Support unnumbered headlines via property

* ox.el (org-export--collect-headline-numbering): Ignore unnumbered headline.
(org-export-get-headline-id,
org-export--collect-unnumbered-headline-id): New functions.
(org-export-numbered-headline-p): Further tests for unnumbered headline.
* ox-odt.el (org-odt-headline, org-odt-link,
org-odt-link--infer-description)
ox-md.el (org-md-headline, org-md-link),
ox-latex.el (org-latex-headline, org.latex-link),
ox-html.el (org-html-headline, org-html-link),
ox-ascii.el (org-ascii-link): Support unnumbered headlines.
* test-ox.el (test-org-export/org-export-get-headline-id): New test.
* OrgOdtStyles.xml: Add styles for unnumbered headings.

etc/styles/OrgOdtStyles.xml

@@ -109,33 +109,52 @@
   </style:style>
   <style:style style:name="Heading_20_1" style:display-name="Heading 1" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="1" style:class="text">
    <style:text-properties fo:font-size="115%" fo:font-weight="bold" style:font-size-asian="115%" style:font-weight-asian="bold" style:font-size-complex="115%" style:font-weight-complex="bold"/>
+   <style:style style:name="Heading_20_1_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_1" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_2" style:display-name="Heading 2" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="2" style:class="text">
    <style:text-properties fo:font-size="14pt" fo:font-style="italic" fo:font-weight="bold" style:font-size-asian="14pt" style:font-style-asian="italic" style:font-weight-asian="bold" style:font-size-complex="14pt" style:font-style-complex="italic" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_2_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_2" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_3" style:display-name="Heading 3" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="3" style:class="text">
    <style:text-properties fo:font-size="14pt" fo:font-weight="bold" style:font-size-asian="14pt" style:font-weight-asian="bold" style:font-size-complex="14pt" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_3_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_3" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_4" style:display-name="Heading 4" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="4" style:class="text">
    <style:text-properties fo:font-size="85%" fo:font-style="italic" fo:font-weight="bold" style:font-size-asian="85%" style:font-style-asian="italic" style:font-weight-asian="bold" style:font-size-complex="85%" style:font-style-complex="italic" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_4_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_4" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_5" style:display-name="Heading 5" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="5" style:class="text">
    <style:text-properties fo:font-size="85%" fo:font-weight="bold" style:font-size-asian="85%" style:font-weight-asian="bold" style:font-size-complex="85%" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_5_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_5" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_6" style:display-name="Heading 6" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="6" style:class="text">
    <style:text-properties fo:font-size="75%" fo:font-weight="bold" style:font-size-asian="75%" style:font-weight-asian="bold" style:font-size-complex="75%" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_6_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_6" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_7" style:display-name="Heading 7" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="7" style:class="text">
    <style:text-properties fo:font-size="75%" fo:font-weight="bold" style:font-size-asian="75%" style:font-weight-asian="bold" style:font-size-complex="75%" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_7_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_7" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_8" style:display-name="Heading 8" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="8" style:class="text">
    <style:text-properties fo:font-size="75%" fo:font-weight="bold" style:font-size-asian="75%" style:font-weight-asian="bold" style:font-size-complex="75%" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_8_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_8" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_9" style:display-name="Heading 9" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="9" style:class="text">
    <style:text-properties fo:font-size="75%" fo:font-weight="bold" style:font-size-asian="75%" style:font-weight-asian="bold" style:font-size-complex="75%" style:font-weight-complex="bold"/>
   </style:style>
+    <style:style style:name="Heading_20_9_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_9" style:list-style-name="">
+    </style:style>
   <style:style style:name="Heading_20_10" style:display-name="Heading 10" style:family="paragraph" style:parent-style-name="Heading" style:next-style-name="Text_20_body" style:default-outline-level="10" style:class="text">
    <style:text-properties fo:font-size="75%" fo:font-weight="bold" style:font-size-asian="75%" style:font-weight-asian="bold" style:font-size-complex="75%" style:font-weight-complex="bold"/>
+  </style:style>
+    <style:style style:name="Heading_20_10_unnumbered" style:family="paragraph" style:parent-style-name="Heading_20_10" style:list-style-name="">
   </style:style>
   <style:style style:name="Heading_20_1.title" style:display-name="Heading 1.title" style:family="paragraph" style:parent-style-name="Heading_20_1">
    <style:paragraph-properties fo:text-align="center" style:justify-single-word="false"/>

lisp/org.el

@@ -15340,7 +15340,7 @@ but in some other way.")
     "LOCATION" "LOGGING" "COLUMNS" "VISIBILITY"
     "TABLE_EXPORT_FORMAT" "TABLE_EXPORT_FILE"
     "EXPORT_OPTIONS" "EXPORT_TEXT" "EXPORT_FILE_NAME"
-    "EXPORT_TITLE" "EXPORT_AUTHOR" "EXPORT_DATE"
+    "EXPORT_TITLE" "EXPORT_AUTHOR" "EXPORT_DATE" "UNNUMBERED"
     "ORDERED" "NOBLOCKING" "COOKIE_DATA" "LOG_INTO_DRAWER" "REPEAT_TO_STATE"
     "CLOCK_MODELINE_TOTAL" "STYLE" "HTML_CONTAINER_CLASS")
   "Some properties that are used by Org-mode for various purposes.

lisp/ox-ascii.el

@@ -1530,9 +1530,13 @@ INFO is a plist holding contextual information."
 	    (let ((number
 		   (org-export-get-ordinal
 		    destination info nil 'org-ascii--has-caption-p)))
-	      (when number
+	      (if number
 		(if (atom number) (number-to-string number)
-		  (mapconcat 'number-to-string number "."))))))))
+		  (mapconcat #'number-to-string number "."))
+		;; Unnumbered headline.
+		(when (eq 'headline (org-element-type destination))
+		  (format "[%s]" (org-export-data
+				  (org-element-property :title destination) info)))))))))
      (t
       (if (not (org-string-nw-p desc)) (format "[%s]" raw-link)
 	(concat (format "[%s]" desc)

lisp/ox-html.el

@@ -2096,8 +2096,7 @@ INFO is a plist used as a communication channel."
 	    ;; Label.
 	    (org-export-solidify-link-text
 	     (or (org-element-property :CUSTOM_ID headline)
-		 (concat "sec-"
-			 (mapconcat #'number-to-string headline-number "-"))))
+		 (org-export-get-headline-id headline info)))
 	    ;; Body.
 	    (concat
 	     (and (not (org-export-low-level-p headline info))
@@ -2321,7 +2320,8 @@ holding contextual information."
   (unless (org-element-property :footnote-section-p headline)
     (let* ((numberedp (org-export-numbered-headline-p headline info))
            (numbers (org-export-get-headline-number headline info))
-           (section-number (mapconcat #'number-to-string numbers "-"))
+           (section-number (and numbers
+				(mapconcat #'number-to-string numbers "-")))
            (level (+ (org-export-get-relative-level headline info)
                      (1- (plist-get info :html-toplevel-hlevel))))
            (todo (and (plist-get info :with-todo-keywords)
@@ -2338,7 +2338,7 @@ holding contextual information."
            (contents (or contents ""))
            (ids (delq nil
                       (list (org-element-property :CUSTOM_ID headline)
-                            (concat "sec-" section-number)
+                            (org-export-get-headline-id headline info)
                             (org-element-property :ID headline))))
            (preferred-id (car ids))
            (extra-ids (mapconcat
@@ -2369,7 +2369,7 @@ holding contextual information."
                   (org-html--container headline info)
                   (format "outline-container-%s"
                           (or (org-element-property :CUSTOM_ID headline)
-                              (concat "sec-" section-number)))
+                              (org-export-get-headline-id headline info)))
                   (concat (format "outline-%d" level)
                           (and extra-class " ")
                           extra-class)
@@ -2808,20 +2808,11 @@ INFO is a plist holding contextual information.  See
 	  ;; Link points to a headline.
 	  (headline
 	   (let ((href
-		  ;; What href to use?
-		  (cond
-		   ;; Case 1: Headline is linked via it's CUSTOM_ID
-		   ;; property.  Use CUSTOM_ID.
-		   ((string= type "custom-id")
-		    (org-element-property :CUSTOM_ID destination))
-		   ;; Case 2: Headline is linked via it's ID property
-		   ;; or through other means.  Use the default href.
-		   ((member type '("id" "fuzzy"))
-		    (format "sec-%s"
-			    (mapconcat 'number-to-string
-				       (org-export-get-headline-number
-					destination info) "-")))
-		   (t (error "Shouldn't reach here"))))
+		  ;; Headline linked via CUSTOM_ID.
+		  (or (and (string= type "custom-id")
+			   (org-element-property :CUSTOM_ID destination))
+		      (org-export-get-headline-id destination info)
+		      (t (error "Shouldn't reach here"))))
 		 ;; What description to use?
 		 (desc
 		  ;; Case 1: Headline is numbered and LINK has no
@@ -3073,13 +3064,16 @@ holding contextual information."
       (let* ((class-num (+ (org-export-get-relative-level parent info)
 			   (1- (plist-get info :html-toplevel-hlevel))))
 	     (section-number
-	      (mapconcat
-	       'number-to-string
-	       (org-export-get-headline-number parent info) "-")))
+	      (and (org-export-numbered-headline-p parent info)
+		   (mapconcat
+		    #'number-to-string
+		    (org-export-get-headline-number parent info) "-"))))
         ;; Build return value.
 	(format "<div class=\"outline-text-%d\" id=\"text-%s\">\n%s</div>"
 		class-num
-		(or (org-element-property :CUSTOM_ID parent) section-number)
+		(or (org-element-property :CUSTOM_ID parent)
+		    section-number
+		    (org-export-get-headline-id parent info))
 		contents)))))
 
 ;;;; Radio Target

lisp/ox-latex.el

@@ -1477,15 +1477,10 @@ holding contextual information."
 			       todo todo-type priority text tags info))
 	   ;; Associate \label to the headline for internal links.
 	   (headline-label
-	    (let ((custom-label
-		   (and (plist-get info :latex-custom-id-labels)
-			(org-element-property :CUSTOM_ID headline))))
-	      (if custom-label (format "\\label{%s}\n" custom-label)
-		(format "\\label{sec-%s}\n"
-			(mapconcat
-			 #'number-to-string
-			 (org-export-get-headline-number headline info)
-			 "-")))))
+	    (format "\\label{%s}\n"
+		    (or (and (plist-get info :latex-custom-id-labels)
+			     (org-element-property :CUSTOM_ID headline))
+			(org-export-get-headline-id headline info))))
 	   (pre-blanks
 	    (make-string (org-element-property :pre-blank headline) 10)))
       (if (or (not section-fmt) (org-export-low-level-p headline info))
@@ -1975,14 +1970,8 @@ INFO is a plist holding contextual information.  See
 	   (let* ((custom-label
 		   (and (plist-get info :latex-custom-id-labels)
 			(org-element-property :CUSTOM_ID destination)))
-		  (label
-		   (or
-		    custom-label
-		    (format "sec-%s"
-			    (mapconcat
-			     #'number-to-string
-			     (org-export-get-headline-number destination info)
-			     "-")))))
+		  (label (or custom-label
+			     (org-export-get-headline-id destination info))))
 	     (if (and (not desc)
 		      (org-export-numbered-headline-p destination info))
 		 (format "\\ref{%s}" label)

lisp/ox-md.el

@@ -204,10 +204,7 @@ a communication channel."
 	    (when (plist-get info :with-toc)
 	      (org-html--anchor
 	       (or (org-element-property :CUSTOM_ID headline)
-		   (concat "sec-"
-			   (mapconcat 'number-to-string
-				      (org-export-get-headline-number
-				       headline info) "-")))
+		   (org-export-get-headline-id headline info))
 	       nil nil info)))
 	   ;; Headline text without tags.
 	   (heading (concat todo priority title))
@@ -330,10 +327,13 @@ a communication channel."
 	   (and contents (concat contents " "))
 	   (format "(%s)"
 		   (format (org-export-translate "See section %s" :html info)
-			   (mapconcat 'number-to-string
-				      (org-export-get-headline-number
-				       destination info)
-				      ".")))))))
+			   (if (org-export-numbered-headline-p destination info)
+			       (mapconcat #'number-to-string
+					  (org-export-get-headline-number
+					   destination info)
+					  ".")
+			     (org-export-data
+			      (org-element-property :title destination) info))))))))
      ((org-export-inline-image-p link org-html-inline-image-rules)
       (let ((path (let ((raw-path (org-element-property :path link)))
 		    (if (not (file-name-absolute-p raw-path)) raw-path
@@ -354,9 +354,13 @@ a communication channel."
 	(if (org-string-nw-p contents) contents
 	  (when destination
 	    (let ((number (org-export-get-ordinal destination info)))
-	      (when number
+	      (if number
 		(if (atom number) (number-to-string number)
-		  (mapconcat 'number-to-string number "."))))))))
+		  (mapconcat #'number-to-string number "."))
+		;; Unnumbered headline.
+		(and (eq 'headline (org-element-type destination))
+		  ;; BUG: shouldn't headlines have a form like [ref](name) in md?
+		  (org-export-data (org-element-property :title headline) info))))))))
      ;; Link type is handled by a special function.
      ((let ((protocol (nth 2 (assoc type org-link-protocols))))
 	(and (functionp protocol)

lisp/ox-odt.el

@@ -1122,7 +1122,7 @@ See `org-odt--build-date-styles' for implementation details."
   (setq text
 	(concat
 	 ;; Section number.
-	 (when section-number (concat section-number ". "))
+	 (and section-number (concat section-number ". "))
 	 ;; Todo.
 	 (when todo
 	   (let ((style (if (member todo org-done-keywords)
@@ -1789,8 +1789,7 @@ INFO is a plist holding contextual information."
 		(org-element-property :title headline) backend info))
 	 (tags (and (plist-get info :with-tags)
 		    (org-export-get-tags headline info)))
-	 (headline-label (concat "sec-" (mapconcat 'number-to-string
-						   headline-number "-")))
+	 (headline-label (org-export-get-headline-id headline info))
 	 (format-function
 	  (if (functionp format-function) format-function
 	    (function*
@@ -1815,10 +1814,9 @@ holding contextual information."
 	   (full-text (org-odt-format-headline--wrap headline nil info))
 	   ;; Get level relative to current parsed data.
 	   (level (org-export-get-relative-level headline info))
+	   (numbered (org-export-numbered-headline-p headline info))
 	   ;; Get canonical label for the headline.
-	   (id (concat "sec-" (mapconcat 'number-to-string
-					 (org-export-get-headline-number
-					  headline info) "-")))
+	   (id (org-export-get-headline-id headline info))
 	   ;; Get user-specified labels for the headline.
 	   (extra-ids (list (org-element-property :CUSTOM_ID headline)
 			    (org-element-property :ID headline)))
@@ -1842,8 +1840,7 @@ holding contextual information."
 	 (and (org-export-first-sibling-p headline info)
 	      (format "\n<text:list text:style-name=\"%s\" %s>"
 		      ;; Choose style based on list type.
-		      (if (org-export-numbered-headline-p headline info)
-			  "OrgNumberedList" "OrgBulletedList")
+		      (if numbered "OrgNumberedList" "OrgBulletedList")
 		      ;; If top-level list, re-start numbering.  Otherwise,
 		      ;; continue numbering.
 		      (format "text:continue-numbering=\"%s\""
@@ -1870,9 +1867,11 @@ holding contextual information."
        (t
 	(concat
 	 (format
-	  "\n<text:h text:style-name=\"%s\" text:outline-level=\"%s\">%s</text:h>"
-	  (format "Heading_20_%s" level)
+	  "\n<text:h text:style-name=\"%s\" text:outline-level=\"%s\" text:is-list-header=\"%s\">%s</text:h>"
+	  (format "Heading_20_%s%s"
+		  level (if numbered "" "_unnumbered"))
 	  level
+	  (if numbered "false" "true")
 	  (concat extra-targets anchored-title))
 	 contents))))))
 
@@ -2643,10 +2642,7 @@ Return nil, otherwise."
   (let* ((genealogy (org-export-get-genealogy destination))
 	 (data (reverse genealogy))
 	 (label (case (org-element-type destination)
-		  (headline
-		   (format "sec-%s" (mapconcat 'number-to-string
-					       (org-export-get-headline-number
-						destination info) "-")))
+		  (headline (org-export-get-headline-id destination info))
 		  (target
 		   (org-element-property :value destination))
 		  (t (error "FIXME: Resolve %S" destination)))))
@@ -2692,11 +2688,15 @@ Return nil, otherwise."
 			      item-numbers "")))))
      ;; Case 2: Locate a regular and numbered headline in the
      ;; hierarchy.  Display its section number.
-     (let ((headline (loop for el in (cons destination genealogy)
-			   when (and (eq (org-element-type el) 'headline)
-				     (not (org-export-low-level-p el info))
-				     (org-export-numbered-headline-p el info))
-			   return el)))
+     (let ((headline
+	    (and
+	     ;; Test if destination is a numbered headline.
+	     (org-export-numbered-headline-p destination info)
+	     (loop for el in (cons destination genealogy)
+		   when (and (eq (org-element-type el) 'headline)
+			     (not (org-export-low-level-p el info))
+			     (org-export-numbered-headline-p el info))
+		   return el))))
        ;; We found one.
        (when headline
 	 (format "<text:bookmark-ref text:reference-format=\"chapter\" text:ref-name=\"OrgXref.%s\">%s</text:bookmark-ref>"
@@ -2776,11 +2776,9 @@ INFO is a plist holding contextual information.  See
 	   ;; If there's a description, create a hyperlink.
 	   ;; Otherwise, try to provide a meaningful description.
 	   (if (not desc) (org-odt-link--infer-description destination info)
-	     (let* ((headline-no
-		     (org-export-get-headline-number destination info))
-		    (label
-		     (format "sec-%s"
-			     (mapconcat 'number-to-string headline-no "-"))))
+	     (let ((label (or (and (string= type "custom-id")
+				   (org-element-property :CUSTOM_ID destination))
+			      (org-export-get-headline-id destination info))))
 	       (format
 		"<text:a xlink:type=\"simple\" xlink:href=\"#%s\">%s</text:a>"
 		label desc))))

lisp/ox.el

@@ -1974,6 +1974,7 @@ Return updated plist."
   ;; properties.
   (nconc
    `(:headline-numbering ,(org-export--collect-headline-numbering data info)
+     :unnumbered-headline-id ,(org-export--collect-unnumbered-headline-id data info)
      :exported-data ,(make-hash-table :test 'eq :size 4001))
    info))
 
@@ -1996,7 +1997,7 @@ OPTIONS is a plist holding export options."
       (if (= min-level 10000) 1 min-level))))
 
 (defun org-export--collect-headline-numbering (data options)
-  "Return numbering of all exportable headlines in a parse tree.
+  "Return numbering of all exportable, numbered headlines in a parse tree.
 
 DATA is the parse tree.  OPTIONS is the plist holding export
 options.
@@ -2007,7 +2008,8 @@ for a footnotes section."
   (let ((numbering (make-vector org-export-max-depth 0)))
     (org-element-map data 'headline
       (lambda (headline)
-	(unless (org-element-property :footnote-section-p headline)
+	(when (and (org-export-numbered-headline-p headline options)
+		   (not (org-element-property :footnote-section-p headline)))
 	  (let ((relative-level
 		 (1- (org-export-get-relative-level headline options))))
 	    (cons
@@ -2019,6 +2021,17 @@ for a footnotes section."
 		   when (> idx relative-level) do (aset numbering idx 0))))))
       options)))
 
+(defun org-export--collect-unnumbered-headline-id (data options)
+  "Return numbering of all exportable, unnumbered headlines.
+DATA is the parse tree.  OPTIONS is the plist holding export
+options.  Unnumbered headlines are numbered as a function of
+occurrence."
+  (let ((num 0))
+    (org-element-map data 'headline
+	(lambda (headline)
+	  (unless (org-export-numbered-headline-p headline options)
+	    (list headline (incf num)))))))
+
 (defun org-export--populate-ignore-list (data options)
   "Return list of elements and objects to ignore during export.
 DATA is the parse tree to traverse.  OPTIONS is the plist holding
@@ -3873,7 +3886,12 @@ INFO is the plist used as a communication channel."
 ;;
 ;; `org-export-get-headline-number' returns the section number of an
 ;; headline, while `org-export-number-to-roman' allows to convert it
-;; to roman numbers.
+;; to roman numbers.  With an optional argument,
+;; `org-export-get-headline-number' returns a number to unnumbered
+;; headlines (used for internal id).
+;;
+;; `org-export-get-headline-id' returns the unique internal id of a
+;; headline.
 ;;
 ;; `org-export-low-level-p', `org-export-first-sibling-p' and
 ;; `org-export-last-sibling-p' are three useful predicates when it
@@ -3908,17 +3926,32 @@ and the last level being considered as high enough, or nil."
       (let ((level (org-export-get-relative-level headline info)))
         (and (> level limit) (- level limit))))))
 
+(defun org-export-get-headline-id (headline info)
+  "Return a unique ID for HEADLINE.
+INFO is a plist holding contextual information."
+  (let ((numbered (org-export-numbered-headline-p headline info)))
+    (concat
+     (if numbered "sec-" "unnumbered-")
+     (mapconcat #'number-to-string
+		(if numbered
+		    (org-export-get-headline-number headline info)
+		  (cdr (assq headline (plist-get info :unnumbered-headline-id)))) "-"))))
+
 (defun org-export-get-headline-number (headline info)
-  "Return HEADLINE numbering as a list of numbers.
+  "Return numbered HEADLINE numbering as a list of numbers.
 INFO is a plist holding contextual information."
-  (cdr (assoc headline (plist-get info :headline-numbering))))
+  (and (org-export-numbered-headline-p headline info)
+       (cdr (assq headline (plist-get info :headline-numbering)))))
 
 (defun org-export-numbered-headline-p (headline info)
   "Return a non-nil value if HEADLINE element should be numbered.
 INFO is a plist used as a communication channel."
-  (let ((sec-num (plist-get info :section-numbers))
-	(level (org-export-get-relative-level headline info)))
-    (if (wholenump sec-num) (<= level sec-num) sec-num)))
+  (unless (org-some
+	   (lambda (head) (org-not-nil (org-element-property :UNNUMBERED head)))
+	   (cons headline (org-export-get-genealogy headline)))
+    (let ((sec-num (plist-get info :section-numbers))
+	  (level (org-export-get-relative-level headline info)))
+      (if (wholenump sec-num) (<= level sec-num) sec-num))))
 
 (defun org-export-number-to-roman (n)
   "Convert integer N into a roman numeral."

testing/lisp/test-ox.el

@@ -1633,6 +1633,68 @@ Paragraph[fn:1]"
        (lambda (h) (org-export-numbered-headline-p h info))
        (plist-put info :section-numbers t)))))
 
+(ert-deftest test-org-export/org-export-get-headline-id ()
+  "Test `org-export-get-headline-id' specifications."
+  ;; Numbered headlines have IDs akin to "sec-N".
+  (should
+   (equal "sec-1"
+	  (org-test-with-parsed-data "* H"
+	    (org-export-get-headline-id
+	     (org-element-map tree 'headline #'identity info t)
+	     info))))
+  ;; The ID of numbered headlines reflect the hierarchy.
+  (should
+   (equal "sec-1-1"
+	  (org-test-with-parsed-data "* H1\n** H2"
+	    (org-export-get-headline-id
+	     (org-element-map tree 'headline
+	       (lambda (h)
+		 (and (equal "H2" (org-element-property :raw-value h)) h))
+	       info t)
+	     info))))
+  ;; Unnumbered headlines have IDs akin to "unnumbered-N".
+  (should
+   (equal "unnumbered-1"
+	  (org-test-with-parsed-data
+	      "* H\n:PROPERTIES:\n:UNNUMBERED: t\n:END:"
+	    (org-export-get-headline-id
+	     (org-element-map tree 'headline #'identity info t)
+	     info))))
+  ;; The ID of Unnumbered headlines do not reflect the hierarchy.
+  (should
+   (equal "unnumbered-2"
+	  (org-test-with-parsed-data
+	      "* H1\n:PROPERTIES:\n:UNNUMBERED: t\n:END:\n** H2"
+	    (org-export-get-headline-id
+	     (org-element-map tree 'headline
+	       (lambda (h)
+		 (and (equal "H2" (org-element-property :raw-value h)) h))
+	       info t)
+	     info))))
+  ;; When #+OPTIONS: num:nil all headlines are unnumbered.
+  (should
+   (equal "unnumbered-1"
+	  (org-test-with-parsed-data "* H\n#+OPTIONS: num:nil"
+	    (org-export-get-headline-id
+	     (org-element-map tree 'headline 'identity info t)
+	     info))))
+  ;; UNNUMBERED ignores inheritance.  Any non-nil value among
+  ;; ancestors disables numbering.
+  (should
+   (org-test-with-parsed-data
+       "* H
+:PROPERTIES:
+:UNNUMBERED: t
+:END:
+** H2
+:PROPERTIES:
+:UNNUMBERED: nil
+:END:
+*** H3"
+     (org-every
+      (lambda (h) (not (org-export-numbered-headline-p h info)))
+      (org-element-map tree 'headline #'identity info)))))
+
 (ert-deftest test-org-export/number-to-roman ()
   "Test `org-export-number-to-roman' specifications."
   ;; If number is negative, return it as a string.