Allow %<num> escapes to capture templates, expanded to text entered in <num>'th prompt

* org-capture.el (org-capture-fill-template): Expand %<num>
escape sequences into text entered for <num>'th %^{PROMPT} escape.

doc/org.texi

@@ -6670,28 +6670,28 @@ these sequences literally, escape the @kbd{%} with a backslash.}  allow
 dynamic insertion of content.  The templates are expanded in the order given here:
 
 @smallexample
-%[@var{file}]     @r{insert the contents of the file given by @var{file}.}
-%(@var{sexp})     @r{evaluate Elisp @var{sexp} and replace with the result.}
-%<...>      @r{the result of format-time-string on the ... format specification.}
-%t          @r{timestamp, date only.}
-%T          @r{timestamp with date and time.}
-%u, %U      @r{like the above, but inactive timestamps.}
-%a          @r{annotation, normally the link created with @code{org-store-link}.}
-%i          @r{initial content, the region when capture is called while the}
+%[@var{file}]     @r{Insert the contents of the file given by @var{file}.}
+%(@var{sexp})     @r{Evaluate Elisp @var{sexp} and replace with the result.}
+%<...>      @r{The result of format-time-string on the ... format specification.}
+%t          @r{Timestamp, date only.}
+%T          @r{Timestamp, with date and time.}
+%u, %U      @r{Like the above, but inactive timestamps.}
+%a          @r{Annotation, normally the link created with @code{org-store-link}.}
+%i          @r{Initial content, the region when capture is called while the}
             @r{region is active.}
             @r{The entire text will be indented like @code{%i} itself.}
-%A          @r{like @code{%a}, but prompt for the description part.}
+%A          @r{Like @code{%a}, but prompt for the description part.}
 %c          @r{Current kill ring head.}
 %x          @r{Content of the X clipboard.}
-%k          @r{title of the currently clocked task.}
-%K          @r{link to the currently clocked task.}
-%n          @r{user name (taken from @code{user-full-name}).}
-%f          @r{file visited by current buffer when org-capture was called.}
-%F          @r{full path of the file or directory visited by current buffer.}
-%:keyword   @r{specific information for certain link types, see below.}
-%^g         @r{prompt for tags, with completion on tags in target file.}
-%^G         @r{prompt for tags, with completion all tags in all agenda files.}
-%^t         @r{like @code{%t}, but prompt for date.  Similarly @code{%^T}, @code{%^u}, @code{%^U}.}
+%k          @r{Title of the currently clocked task.}
+%K          @r{Link to the currently clocked task.}
+%n          @r{User name (taken from @code{user-full-name}).}
+%f          @r{File visited by current buffer when org-capture was called.}
+%F          @r{Full path of the file or directory visited by current buffer.}
+%:keyword   @r{Specific information for certain link types, see below.}
+%^g         @r{Prompt for tags, with completion on tags in target file.}
+%^G         @r{Prompt for tags, with completion all tags in all agenda files.}
+%^t         @r{Like @code{%t}, but prompt for date.  Similarly @code{%^T}, @code{%^u}, @code{%^U}.}
             @r{You may define a prompt like @code{%^@{Birthday@}t}.}
 %^C         @r{Interactive selection of which kill or clip to use.}
 %^L         @r{Like @code{%^C}, but insert as link.}
@@ -6700,6 +6700,9 @@ dynamic insertion of content.  The templates are expanded in the order given her
             @r{You may specify a default value and a completion table with}
             @r{%^@{prompt|default|completion2|completion3...@}.}
             @r{The arrow keys access a prompt-specific history.}
+%<n>        @r{Insert the text entered for at the nth %^{prompt}, where <n>
+            @r{represents a digit, 1 to 9.}
+%?          @r{After completing the template, position cursor here.}
 @end smallexample
 
 @noindent

lisp/org-capture.el

@@ -248,6 +248,8 @@ be replaced with content and expanded in this order:
               A default value and a completion table ca be specified like this:
               %^{prompt|default|completion2|completion3|...}.
   %?          After completing the template, position cursor here.
+  %<n>        Insert the text entered for at the nth %^{prompt}, where <n>
+              represents a digit, 1 to 9.
 
 Apart from these general escapes, you can access information specific to the
 link type that is created.  For example, calling `org-capture' in emails
@@ -1326,7 +1328,7 @@ The template may still contain \"%?\" for cursor positioning."
 	 (org-startup-folded nil)
 	 (org-inhibit-startup t)
 	 org-time-was-given org-end-time-was-given x
-	 prompt completions char time pos default histvar)
+	 prompt completions char time pos default histvar strings)
 
     (setq org-store-link-plist
 	  (plist-put org-store-link-plist :annotation v-a)
@@ -1468,11 +1470,21 @@ The template may still contain \"%?\" for cursor positioning."
 				   nil nil (list org-end-time-was-given)))
 	   (t
 	    (let (org-completion-use-ido)
-	      (insert (org-completing-read-no-i
-		       (concat (if prompt prompt "Enter string")
-			       (if default (concat " [" default "]"))
-			       ": ")
-		       completions nil nil nil histvar default)))))))
+	      (push (org-completing-read-no-i
+		     (concat (if prompt prompt "Enter string")
+			     (if default (concat " [" default "]"))
+			     ": ")
+		     completions nil nil nil histvar default)
+		    strings)
+	      (insert (car strings)))))))
+      ;; Replace %n escapes with nth %^{...} string
+      (setq strings (nreverse strings))
+      (goto-char (point-min))
+      (while (re-search-forward "%\\([1-9]\\)+" nil t)
+	(unless (org-capture-escaped-%)
+	  (replace-match
+	   (nth (1- (string-to-number (match-string 1))) strings)
+	   nil t)))
       ;; Make sure there are no empty lines before the text, and that
       ;; it ends with a newline character
       (goto-char (point-min))