diff --git a/documentation/ref-manual/ref-variables.xml b/documentation/ref-manual/ref-variables.xml
index 5556e56cba..8f3429ff08 100644
--- a/documentation/ref-manual/ref-variables.xml
+++ b/documentation/ref-manual/ref-variables.xml
@@ -5062,6 +5062,10 @@ recipes-graphics/xorg-font/font-alias_1.0.3.bb:PR = "${INC_PR}.3"
                     set it in a recipe that inherits the
                     <link linkend='ref-classes-qmake*'><filename>qmake_base</filename></link>
                     class.
+                    If you do not set this variable, all
+                    <filename>.pro</filename> files in the directory pointed to
+                    by <link linkend='var-S'><filename>S</filename></link>
+                    will be built by default.
                 </para>
             </glossdef>
         </glossentry>