diff --git a/product/ERP5/PropertySheet/Reference.py b/product/ERP5/PropertySheet/Reference.py
index 8d5e3ea3fffed306d3a1f47ec0c49defbe1b4def..7e3143803b23386b647655bacd5e6d8fcdef1324 100755
--- a/product/ERP5/PropertySheet/Reference.py
+++ b/product/ERP5/PropertySheet/Reference.py
@@ -48,6 +48,10 @@ class Reference:
             'description' : 'The references of the document for default destinations',
             'type'        : 'string',
             'mode'        : 'w' },
+        {   'id'          : 'grouping_reference',
+            'description' : 'A reference which allows to unify multiple objects',
+            'type'        : 'string',
+            'mode'        : 'w' },
         {   'id'          : 'document_reference', # XXX ERROR - we already have a reference
             'description' : 'The references of the document itself',
             'type'        : 'string',