Help understanding dom0 package issues

I thought the introduction of sys-audio (and sys-gui, but that’s less mature IIUC) meant these things are separate.

Where is that introduction? I don’t have a sys-audio on my system (installed from scratch as 4.1 then upgraded all the way to 4.2.1) and I don’t find any official doc when searching for ‘sys-audio’. sys-gui didn’t work for me either.

So, if these two have bee introduced somehow and I have missed the news, could you please link to the relevant info?