[Seaside] How to dynamically add to list of sub-components with Ajax?

[itsme213]

I have domain classes House and Room, and SUComponents HouseView and 
RoomView, each directly editable.

HouseView contains (via inst-var) a list of RoomViews and a '++' anchor 
which adds a new room to the House.

How do I get the '++' to correctly update only the list of RoomViews in the 
browser (via Ajax)? What should #children look like for HouseView?

Thanks.