diff --git a/docs/add_ons.txt b/docs/add_ons.txt
index d72e92b018..90c98b7176 100644
--- a/docs/add_ons.txt
+++ b/docs/add_ons.txt
@@ -128,6 +128,8 @@ A collection of template filters that implement these common markup languages:
     * Markdown
     * ReST (ReStructured Text)
 
+For documentation, read the source code in django/contrib/markup/templatetags/markup.py.
+
 redirects
 =========