Macro expansion $APPDIR not explained in docs

http://docs.oracle.com/javafx/2/deployment/javafx_ant_task_reference.htm does not contain a description for the macro expansion $APPDIR.

For instance
            <fx:platform>
              <fx:jvmarg value="-Djava.policy.file=$APPDIR/app/whatever.policy"/>
            </fx:platform>

would get expanded during launch to something like

-Djava.policy.file=/Users/cooluse/mydev/TestPackager/dist/bundles/Test Packager.app/Contents/app/whatever.policy