Document that we use separate semantic version numbers for TF Lite, and for the

TF Lite Extension APIs (custom ops + delegates), than for TensorFlow itself.

PiperOrigin-RevId: 565723934

Author: fergushenderson

site/en/guide/versions.md

@@ -61,6 +61,41 @@ patch versions.  The public APIs consist of
 
     *   [tensorflow/c/c_api.h](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/c/c_api.h))
 
+*   The following protocol buffer files:
+
+    *   [`attr_value`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/attr_value.proto)
+    *   [`config`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/protobuf/config.proto)
+    *   [`event`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/util/event.proto)
+    *   [`graph`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/graph.proto)
+    *   [`op_def`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/op_def.proto)
+    *   [`reader_base`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/reader_base.proto)
+    *   [`summary`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/summary.proto)
+    *   [`tensor`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/tensor.proto)
+    *   [`tensor_shape`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/tensor_shape.proto)
+    *   [`types`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/types.proto)
+
+<a name="lite"></a>
+
+## Separate version number for TensorFlow Lite
+
+Currently TensorFlow Lite is distributed as a part of TensorFlow. However, we
+reserve the right to in future release changes to the TensorFlow Lite APIs on a
+different schedule than for the other TensorFlow APIs, or even to move
+TensorFlow Lite into a separate source distribution and/or a separate source
+repository than TensorFlow.
+
+Because of this, we use a different version number for TensorFlow Lite
+(`TFLITE_VERSION_STRING` in `tensorflow/lite/version.h`, and `TfLiteVersion()`
+in `tensorflow/lite/c/c_api.h`) than for TensorFlow (`TF_VERSION_STRING` in
+`tensorflow/core/public/version.h`, and `TF_Version()` in
+`tensorflow/c/c_api.h`). Currently, these two version numbers happen to have the
+same value. But in future, they may diverge; for example, we may increment the
+major version number for TensorFlow Lite without incrementing the major version
+number for TensorFlow, or vice versa.
+
+The API surface that is covered by the TensorFlow Lite version number is
+comprised of the following public APIs:
+
 *   The TensorFlow Lite C API:
 
     *   [tensorflow/lite/c/c_api.h](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/lite/c/c_api.h)
@@ -108,20 +143,43 @@ patch versions.  The public APIs consist of
         *   TensorFlowLite.swift
         *   Tensor.swift
 
-*   The following protocol buffer files:
+Experimental symbols are not covered; see [below](#not_covered) for details.
 
-    *   [`attr_value`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/attr_value.proto)
-    *   [`config`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/protobuf/config.proto)
-    *   [`event`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/util/event.proto)
-    *   [`graph`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/graph.proto)
-    *   [`op_def`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/op_def.proto)
-    *   [`reader_base`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/reader_base.proto)
-    *   [`summary`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/summary.proto)
-    *   [`tensor`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/tensor.proto)
-    *   [`tensor_shape`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/tensor_shape.proto)
-    *   [`types`](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/core/framework/types.proto)
+## Separate version number for TensorFlow Lite Extension APIs
+
+TensorFlow Lite provides C APIs for extending the TensorFlow Lite interpreter
+with "custom ops", which provide user-defined operations in a graph, or
+"delegates", which allow delegating the computation for a graph (or for a subset
+of a graph) to a custom backend. These APIs, which we collectively call the
+"TensorFlow Lite Extension APIs", require more intimate dependencies on some of
+the details of the TensorFlow Lite implementation.
+
+We reserve the right to in future release changes to these APIs, potentially
+including non-backwards-compatible changes, on a different schedule than for the
+other TensorFlow Lite APIs. So we use a different version number for the
+TensorFlow Lite Extension APIs than the version numbers for TensorFlow Lite or
+TensorFlow (which were described in the previous section). The version number
+for the TensorFlow Lite Extension APIs is currently the same as the version
+number for TensorFlow and TensorFlow Lite. But in future, they may diverge; for
+example, we may increment the major version number for the TensorFlow Lite
+Extension APIs without incrementing the major version number for TensorFlow
+Lite, or vice versa.
+
+The API surface that is covered by the TensorFlow Lite Extension APIs version
+number is comprised of the following public APIs:
+
+```
+*   [tensorflow/lite/c/c_api_opaque.h](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/lite/c/c_api_opaque.h)
+*   [tensorflow/lite/c/common.h](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/lite/c/common.h)
+*   [tensorflow/lite/c/builtin_op_data.h](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/lite/c/builtin_op_data.h)
+*   [tensorflow/lite/builtin_ops.h](https://github.com/tensorflow/tensorflow/blob/master/tensorflow/lite/builtin_ops.h)
+```
+
+Again, experimental symbols are not covered; see [below](#not_covered) for
+details.
+
+<e name="not_covered"></a>
 
-<a name="not_covered"></a>
 ## What is *not* covered
 
 Some parts of TensorFlow can change in backward incompatible ways at any point.
@@ -132,11 +190,11 @@ These include:
     particular, the following are not covered by any compatibility guarantees:
 
     -   any symbol in the `tf.contrib` module or its submodules;
-    -   any symbol (module, function, argument, property, class, or constant)
-        whose name contains `experimental` or `Experimental`; or
-    -   any symbol whose fully qualified name includes a module or class which
-        is itself experimental. This includes fields and submessages of any
-        protocol buffer called `experimental`.
+    -   any symbol (module, function, argument, property, class, constant, type,
+        package, etc.) whose name contains `experimental` or `Experimental`; or
+    -   any symbol whose fully qualified name includes a module or class or
+        package which is itself experimental. This includes fields and
+        submessages of any protocol buffer called `experimental`.
 
 *   **Other languages**: TensorFlow APIs in languages other than Python and C,
     such as: