chore: import upstream snapshot with attribution

docs/docsgen/source/api/serialization.md

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+(l-serialization)=
+
+# Serialization
+
+## Save a model and any Proto class
+
+This ONNX graph needs to be serialized into one contiguous
+memory buffer. Method `SerializeToString` is available
+in every ONNX objects.
+
+```
+with open("model.onnx", "wb") as f:
+    f.write(onnx_model.SerializeToString())
+```
+
+This method has the following signature.
+
+```{eval-rst}
+.. autoclass:: onnx.ModelProto
+    :members: SerializeToString
+```
+
+Every Proto class implements method `SerializeToString`.
+Therefore the following code works with any class described
+in page {ref}`l-onnx-classes`.
+
+```
+with open("proto.pb", "wb") as f:
+    f.write(proto.SerializeToString())
+```
+
+Next example shows how to save a {ref}`l-nodeproto`.
+
+```{eval-rst}
+.. exec_code::
+
+    from onnx import NodeProto
+
+    node = NodeProto()
+    node.name = "example-type-proto"
+    node.op_type = "Add"
+    node.input.extend(["X", "Y"])
+    node.output.extend(["Z"])
+
+    with open("node.pb", "wb") as f:
+        f.write(node.SerializeToString())
+```
+
+## Load a model
+
+Following function only automates the loading of a class
+{ref}`l-modelproto`. Next sections shows how to restore
+any other proto class.
+
+```{eval-rst}
+.. autofunction:: onnx.load
+```
+
+```
+from onnx import load
+
+onnx_model = load("model.onnx")
+```
+
+Or:
+
+```
+from onnx import load
+
+with open("model.onnx", "rb") as f:
+    onnx_model = load(f)
+```
+
+Next function does the same from a bytes array.
+
+```{eval-rst}
+.. autofunction:: onnx.load_model_from_string
+
+```
+
+(l-onnx-load-data)=
+
+## Load a Proto
+
+Proto means here any type containing data including a model, a tensor,
+a sparse tensor, any class listed in page {ref}`l-onnx-classes`.
+The user must know the type of the data he needs to restore
+and then call method `ParseFromString`.
+[protobuf](https://developers.google.com/protocol-buffers)
+does not store any information about the class
+of the saved data. Therefore, this class must be known before
+restoring an object.
+
+```{eval-rst}
+.. autoclass:: onnx.ModelProto
+    :members: ParseFromString
+```
+
+Next example shows how to restore a {ref}`l-nodeproto`.
+
+```{eval-rst}
+.. exec_code::
+
+    from onnx import NodeProto
+
+    tp2 = NodeProto()
+    with open("node.pb", "rb") as f:
+        content = f.read()
+
+    tp2.ParseFromString(content)
+
+    print(tp2)
+```
+
+A shortcut exists for {ref}`l-tensorproto`:
+
+```{eval-rst}
+.. autofunction:: onnx.load_tensor_from_string
+```