diff --git a/apex/constants.go b/apex/constants.go
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+++ b/apex/constants.go
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+// Copyright (C) 2022 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package apex
+
+// This file contains branch specific constants. They are stored in a separate
+// file to minimise the potential of merge conflicts between branches when
+// the code from the package is changed.
+
+// The default manifest version for all the modules on this branch.
+// This version code will be used only if there is no version field in the
+// module's apex_manifest.json. Release branches have their version injected
+// into apex_manifest.json by the tooling and will not use the version set
+// here. Developers can also set the version field locally in the
+// apex_manifest.json to build a module with a specific version.
+//
+// The value follows the schema from go/mainline-version-codes, and is chosen
+// based on the branch such that the builds from testing and development
+// branches will have a version higher than the prebuilts.
+// Versions per branch:
+// * x-dev           - xx0090000 (where xx is the branch SDK level)
+// * AOSP            - xx9990000
+// * x-mainline-prod - xx9990000
+// * master          - 990090000
+const defaultManifestVersion = "339990000"