howdy do back
this is just like three plating a ceiling rose but you just do it at the switch so you only have one t+e at the rose, easier for connecting downlighters etc, less wires. so you would have at the switch, in t+e anyways -
a feed in (t+e)
a feed out (t+e)
and a switch line (t+e that goes to the rose)
so you put all your neutrals in the connector, all your earths together, then the feed in and feed out lives in one half of the switch and the switch line out to the rose on the other half.
to add to this from the switch you would connect to the neutrals, connect to the earths then connect to the feed in feed out side of the lives. this would give you L N E to take where you wish a spur.
hope this helps