diff --git a/doc/misc/gnus.texi b/doc/misc/gnus.texi
index 50eeb3efa3..c9f7491d5b 100644
--- a/doc/misc/gnus.texi
+++ b/doc/misc/gnus.texi
@@ -20394,6 +20394,36 @@ Score File Format
 @end enumerate
 
 @cindex score file atoms
+@item score-fn
+The value of this entry should be one or more user-defined function
+names in parentheses. Each function will be called in order and the
+returned value is required to be an integer.
+
+@example
+        (score-fn (custom-scoring))
+@end example
+
+The user-defined function is called with an associative list with the
+keys @code{number subject from date id refs chars lines xref extra}
+followed by the article's score before the function is run.
+
+The following (somewhat contrived) example shows how to use a
+user-defined function that increases an article's score by 10 if the
+year of the article's date is also mentioned in its subject.
+
+@example
+        (defun custom-scoring (article-alist score)
+          (let ((subject (cdr (assoc 'subject article-alist)))
+                (date (cdr (assoc 'date article-alist))))
+            (if (string-match (number-to-string
+                               (nth 5 (parse-time-string date)))
+                              subject)
+                10)))
+@end example
+
+@code{score-fn} entries are permanent and can only be added or
+modified directly in the @code{SCORE} file.
+
 @item mark
 The value of this entry should be a number.  Any articles with a score
 lower than this number will be marked as read.