What does the "backup<n>" parameter do in a linkdevice URI?

[MatzFan]

Hi

I've just added a device to my account with a URI in the following form and just wondered if someone could explain what the "backup4" param means at the end? I've not noticed this when previously adding devices. Thanks.

$ signal-cli -u +xxxxxxxxxxxx addDevice --uri "sgnl://linkdevice?uuid=xxxxxxxxxxxxxxxxxx&pub_key=xxxxxxxxxxxxxxxxxxxxxxxx&capabilities=backup4"

[chairmantheboring]

It's used for Signal devices to communicate that it supports the new message synchronization feature (and presumably, probably also communicate in the future that the device can download cloud backups (something Signal is working on right now)).

Signal-cli doesn't currently implement these features afaik, since I do not believe it creates a persistent message database.