ZP-622 added HIERARCHYNOTIFICATION constant to the IBackend.

Released under the Affero GNU General Public License (AGPL) version 3.

src/lib/interface/ibackend.php

@@ -46,6 +46,7 @@
 ************************************************/
 
 interface IBackend {
+    const HIERARCHYNOTIFICATION = 'hierarchynotification';
     /**
      * Returns a IStateMachine implementation used to save states
      *