diff --git a/private/compat/31.0/31.0.cil b/private/compat/31.0/31.0.cil
index 0e90912..b0df314 100644
--- a/private/compat/31.0/31.0.cil
+++ b/private/compat/31.0/31.0.cil
@@ -9,6 +9,7 @@
 (type vr_hwc)
 (type vr_hwc_exec)
 
+;; mapping information from ToT policy's types to 31.0 policy's types.
 (expandtypeattribute (DockObserver_service_31_0) true)
 (expandtypeattribute (IProxyService_service_31_0) true)
 (expandtypeattribute (aac_drc_prop_31_0) true)
diff --git a/private/compat/31.0/31.0.compat.cil b/private/compat/31.0/31.0.compat.cil
index 628abfc..787c92a 100644
--- a/private/compat/31.0/31.0.compat.cil
+++ b/private/compat/31.0/31.0.compat.cil
@@ -1 +1,3 @@
-;; This file can't be empty.
+;; complement CIL file for compatibility between ToT policy and 31.0 vendors.
+;; will be compiled along with other normal policy files, on 31.0 vendors.
+;;
diff --git a/private/compat/31.0/31.0.ignore.cil b/private/compat/31.0/31.0.ignore.cil
index a5a3475..0e39f3e 100644
--- a/private/compat/31.0/31.0.ignore.cil
+++ b/private/compat/31.0/31.0.ignore.cil
@@ -1,6 +1,6 @@
-;; new_objects - a collection of types that have been introduced that have no
-;;   analogue in older policy.  Thus, we do not need to map these types to
-;;   previous ones.  Add here to pass checkapi tests.
+;; new_objects - a collection of types that have been introduced with ToT policy
+;;   that have no analogue in 31.0 policy.  Thus, we do not need to map
+;;   these types to previous ones.  Add here to pass checkapi tests.
 (type new_objects)
 (typeattribute new_objects)
 (typeattributeset new_objects