diff --git a/docs/main_window_chapter.sgml b/docs/main_window_chapter.sgml
index b670839d26bd333cc2b22531f80893508648eb73..7dc2bee94c0f6a3e6051ded94b8bd94adb913a9a 100644
--- a/docs/main_window_chapter.sgml
+++ b/docs/main_window_chapter.sgml
@@ -265,5 +265,6 @@ menu items which allow the maximum window size to be set.
     </PARA>
   </SECT1>
 
+&validator;
 &mousebuttons;
 </CHAPTER>