1 files changed, 25 insertions, 5 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index 63951b92bb2..45bcccbb6e5 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1996,14 +1996,34 @@ STRING should be given if the last search was by `string-match' on STRING."
         (buffer-substring-no-properties (match-beginning num)
                                         (match-end num)))))
 
-(defun looking-back (regexp &optional limit)
+(defun looking-back (regexp &optional limit greedy)
   "Return non-nil if text before point matches regular expression REGEXP.
 Like `looking-at' except matches before point, and is slower.
 LIMIT if non-nil speeds up the search by specifying how far back the
-match can start."
-  (not (null
-        (save-excursion
-          (re-search-backward (concat "\\(?:" regexp "\\)\\=") limit t)))))
+match can start.
+
+If GREEDY is non-nil, extend the match backwards as far as possible,
+stopping when a single additional previous character cannot be part
+of a match for REGEXP."
+  (let ((start (point))
+        (pos
+         (save-excursion
+           (and (re-search-backward (concat "\\(?:" regexp "\\)\\=") limit t)
+                (point)))))
+    (if (and greedy pos)
+        (save-restriction
+          (narrow-to-region (point-min) start)
+          (while (and (> pos (point-min))
+                      (save-excursion
+                        (goto-char pos)
+                        (backward-char 1)
+                        (looking-at (concat "\\(?:"  regexp "\\)\\'"))))
+            (setq pos (1- pos)))
+          (save-excursion
+            (goto-char pos)
+            (looking-at (concat "\\(?:"  regexp "\\)\\'")))))
+    (not (null pos))))
+
 
 (defconst split-string-default-separators "[ \f\t\n\r\v]+"
   "The default value of separators for `split-string'.