Constant PARKED_LOGICAL_SIZE 

pub const PARKED_LOGICAL_SIZE: (i32, i32);

The logical size a parked screen is held at. A nested session lays its desktop out across every screen it has, including one waiting here: at the size of a real screen it would double the session’s coordinate space, sending anything a client centres on the desktop (X11 applications place themselves) onto the screen nobody is watching. Small enough not to move that centre, large enough to lay out on; place_window_on_output configures the real size the moment the screen is given an output.