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+Extensions
+==========
+
+.. currentmodule:: websockets.extensions
+
+The WebSocket protocol supports extensions_.
+
+At the time of writing, there's only one `registered extension`_ with a public
+specification, WebSocket Per-Message Deflate.
+
+.. _extensions: https://www.rfc-editor.org/rfc/rfc6455.html#section-9
+.. _registered extension: https://www.iana.org/assignments/websocket/websocket.xhtml#extension-name
+
+Per-Message Deflate
+-------------------
+
+.. automodule:: websockets.extensions.permessage_deflate
+
+    :mod:`websockets.extensions.permessage_deflate` implements WebSocket
+    Per-Message Deflate.
+
+    This extension is specified in :rfc:`7692`.
+
+    Refer to the :doc:`topic guide on compression <../topics/compression>` to
+    learn more about tuning compression settings.
+
+    .. autoclass:: ClientPerMessageDeflateFactory
+
+    .. autoclass:: ServerPerMessageDeflateFactory
+
+Base classes
+------------
+
+.. automodule:: websockets.extensions
+
+    :mod:`websockets.extensions` defines base classes for implementing
+     extensions.
+
+    Refer to the :doc:`how-to guide on extensions <../howto/extensions>` to
+    learn more about writing an extension.
+
+    .. autoclass:: Extension
+
+        .. autoattribute:: name
+
+        .. automethod:: decode
+
+        .. automethod:: encode
+
+    .. autoclass:: ClientExtensionFactory
+
+        .. autoattribute:: name
+
+        .. automethod:: get_request_params
+
+        .. automethod:: process_response_params
+
+    .. autoclass:: ServerExtensionFactory
+
+        .. automethod:: process_request_params