diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 1f7604ba64..eaa5f4e490 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -13549,6 +13549,16 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
                     For these cases, the options are added to
                     <filename>UNKNOWN_CONFIGURE_WHITELIST</filename>.
                 </para>
+
+                <para>
+                    The test for
+                    <filename>UNKNOWN_CONFIGURE_WHITELIST</filename> is part
+                    of the
+                    <link linkend='ref-classes-insane'><filename>insane</filename></link>
+                    class and is only enabled if the recipe inherits the
+                    <link linkend='ref-classes-autotools'><filename>autotools</filename></link>
+                    class.
+                </para>
             </glossdef>
         </glossentry>