new flag at end of CREATE_PLAYBACK_STREAM:
bool relative_volume
+
+## v18, implemented by >= 0.9.22
+
+new flag at end of CREATE_PLAYBACK_STREAM:
+
+ bool passthrough
+
+## v19, implemented by >= 0.9.22
+
+New flag at the end of sink input and source output introspection data:
+
+ bool corked
+
+## v20, implemented by >= 1.0
+
+Two new flags at the end of sink input introspection data:
+
+ bool has_volume
+ bool volume_writable
+
+## v21, implemented by >= 1.0
+
+Changes for format negotiation in the extended API.
+
+New fields PA_COMMAND_CREATE_PLAYBACK_STREAM:
+
+ uint8_t n_formats
+ format_info format1
+ ...
+ format_info formatn
+
+One new field in reply from PA_COMMAND_CREATE_PLAYBACK_STREAM:
+
+ format_info format
+
+New fields in reply from PA_COMMAND_GET_SINK_INFO (and thus
+PA_COMMAND_GET_SINK_INFO_LIST)
+
+ uint8_t n_formats
+ format_info format1
+ ...
+ format_info formatn
+
+One new field in reply from PA_COMMAND_GET_SINK_INPUT_INFO (and thus
+PA_COMMAND_GET_SINK_INPUT_INFO_LIST)
+
+ format_info format
+
+## v22, implemented by >= 1.0
+
+New fields PA_COMMAND_CREATE_RECORD_STREAM:
+
+ uint8_t n_formats
+ format_info format1
+ ...
+ format_info formatn
+
+One new field in reply from PA_COMMAND_CREATE_RECORD_STREAM:
+
+ format_info format
+
+New fields in reply from PA_COMMAND_GET_SOURCE_INFO (and thus
+PA_COMMAND_GET_SOURCE_INFO_LIST)
+
+ uint8_t n_formats
+ format_info format1
+ ...
+ format_info formatn
+
+Five new fields in reply from PA_COMMAND_GET_SOURCE_OUTPUT_INFO (and thus
+PA_COMMAND_GET_SOURCE_OUTPUT_INFO_LIST)
+
+ format_info format
+ volume
+ bool mute
+ bool has_volume
+ bool volume_writable
+
+## v23, implemented by >= 1.0
+
+New field in PA_COMMAND_UNDERFLOW:
+
+ int64_t index
+
+#### If you just changed the protocol, read this
+## module-tunnel depends on the sink/source/sink-input/source-input protocol
+## internals, so if you changed these, you might have broken module-tunnel.
+## Don't forget to test module-tunnel-{source,sink} when pushing protocol
+## changes.