Comment 2 for bug 1986660

That's not really discoverable as a reference though. I wouldn't expect "examples" to contain a definitive reference, and nor a Discourse post about a feature that as far as I know isn't pointed to from any definitive documentation. Same with apt_preferences - I do expect to find information about scoring and the syntax of preferences.d/ files in there, but if I want a reference to a configuration option, it's not obvious to look there.