diff --git a/src/ZODB/interfaces.py b/src/ZODB/interfaces.py
index a5541045a..e73016d78 100644
--- a/src/ZODB/interfaces.py
+++ b/src/ZODB/interfaces.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 ##############################################################################
 #
 # Copyright (c) Zope Corporation and Contributors.
@@ -274,9 +275,9 @@ class IStorageWrapper(Interface):
     - Out-of-band invalidation support
 
       A storage can notify it's wrapper of object invalidations that
-      don't occur due to direct operations on the storage.  Currently
-      this is only used by ZEO client storages to pass invalidation
-      messages sent from a server.
+      don't occur due to direct operations on the storage. This is used
+      by the client part of non-IMVCCStorage storages like ZEO and NEO
+      to pass invalidation messages sent from a storage server.
 
     - Record-reference extraction
 
@@ -312,6 +313,15 @@ def invalidate(transaction_id, oids):
 
         The oids argument is an iterable of object identifiers.
 
+        Unless the cache needs to be completely cleared via
+        invalidateCache event, the wrapped storage calls invalidate for
+        all transactions in the order as they are committed. For every
+        transaction the full set of its objects - both modified and just
+        created - is reported.
+
+        invalidate(tid) is always called before the storage starts to
+        report its lastTransaction() ≥ tid.
+
         The version argument is provided for backward
         compatibility. If passed, it must be an empty string.
 
@@ -1203,13 +1213,18 @@ def release():
     def poll_invalidations():
         """Poll the storage for external changes.
 
-        Returns either a sequence of OIDs that have changed, or None.  When a
-        sequence is returned, the corresponding objects should be removed
-        from the ZODB in-memory cache.  When None is returned, the storage is
-        indicating that so much time has elapsed since the last poll that it
-        is no longer possible to enumerate all of the changed OIDs, since the
-        previous transaction seen by the connection has already been packed.
-        In that case, the ZODB in-memory cache should be cleared.
+        Returns either None, or a sequence of OIDs with the full set of
+        objects that have been created or changed since the previous
+        call to poll_invalidations.
+
+        When a sequence is returned, the corresponding objects should be
+        removed from the ZODB in-memory cache.
+
+        When None is returned, the storage is indicating that so much time has
+        elapsed since the last poll that it is no longer possible to enumerate
+        all of the changed OIDs, since the previous transaction seen by the
+        connection has already been packed. In that case, the ZODB in-memory
+        cache should be cleared.
         """
 
     def sync(force=True):