diff --git a/lisp/org.el b/lisp/org.el
index e34ec1a67..366c8dd21 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -3321,6 +3321,8 @@ When nil, the \\name form remains in the buffer."
 (defvar org-emph-re nil
   "Regular expression for matching emphasis.
 After a match, the match groups contain these elements:
+0  The match of the full regular expression, including the characters
+     before and after the proper match
 1  The character before the proper match, or empty at beginning of line
 2  The proper match, including the leading and trailing markers
 3  The leading marker like * or /, indicating the type of highlighting