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Short answer: you should not use them manually and therefore they are not documented.
These are internal routing arguments to handle the case of bi-directional routing with message having multiple arguments.
They are used when an OSC message with at least 2 arguments are configured with two MIDI CC. When the MIDI host replies, the received message (/midi/ccXY/Z) only have 1 argument. Therefore, in order to send the correct message back to the OSC device, we must build a OSC routing for each MIDI CC that will use and/or update the current values of the OSC device.