public function propFindEarly(DAV\PropFind $propFind, DAV\INode $node)
    {
        if ($node instanceof ISharedCalendar) {
            $propFind->handle('{'.Plugin::NS_CALENDARSERVER.'}invite', function () use ($node) {
                return new Xml\Property\Invite(
                    $node->getInvites()
                );
            });
        }
    }