Index: lib/python/Zope2/Startup/zopeschema.xml
===================================================================
--- lib/python/Zope2/Startup/zopeschema.xml	(revision 4273)
+++ lib/python/Zope2/Startup/zopeschema.xml	(working copy)
@@ -718,6 +718,16 @@
      <metadefault>1000</metadefault>
   </key>
 
+  <!-- Note: we would like to use 'importable_name' as datatype. However,
+    the name may not yet be importable (typical phase ZConfig problem) -->
+  <key name="session-transient-object-container-class"
+       datatype="dotted-name"
+       >
+     <description>
+     An optional Python object implementing a "TransientObjectContainer".
+     </description>
+     <metadefault>Products.Transience.Transience.TransientObjectContainer</metadefault>
+  </key>
   <key name="session-add-notify-script-path"
        handler="session_add_notify_script_path">
      <description>
Index: lib/python/OFS/Application.py
===================================================================
--- lib/python/OFS/Application.py	(revision 4273)
+++ lib/python/OFS/Application.py	(working copy)
@@ -405,6 +405,15 @@
             addnotify = getattr(config, 'session_add_notify_script_path', None)
             delnotify = getattr(config, 'session_delete_notify_script_path',
                                 None)
+            # DM-2008-10-20: make "TransientObjectContainer" class customizable
+            toc_class = getattr(config,
+                                'session_transient_object_container_class',
+                                None)
+            if toc_class is None: toc_class = TransientObjectContainer
+            else:
+                LOG.info("using transient object container class %s" % toc_class)
+                from Zope2.Startup.datatypes import importable_name
+                toc_class = importable_name(toc_class)
             default_limit = 1000
             default_period_secs = 20
             default_timeout_mins = 20
@@ -427,7 +436,8 @@
                 delnotify=None
 
             if 1:  # Preserve indentation for diff
-                toc = TransientObjectContainer('session_data',
+                # DM-2008-10-20: make "TransientObjectContainer" class customizable
+                toc = toc_class(               'session_data',
                                                'Session Data Container',
                                                timeout_mins = timeout_spec,
                                                addNotification = addnotify,