Index: /trunk/doc/manual/en_US/user_GuestAdditions.xml
===================================================================
--- /trunk/doc/manual/en_US/user_GuestAdditions.xml	(revision 35018)
+++ /trunk/doc/manual/en_US/user_GuestAdditions.xml	(revision 35019)
@@ -1181,4 +1181,10 @@
                 read/write.</para>
               </note></para>
+
+              <para>The guest property
+              <computeroutput>/VirtualBox/GuestAdd/SharedFolders/MountDir</computeroutput>
+              determines the absolute mount directory that is used for all auto-mounted
+              Shared Folders. When no value is specified the standard media or mount
+              directory is used according to the guest OS.</para>
           </listitem>