Function mapped 

fn mapped(state: &AppState, window: &Window, id: WindowId) -> bool

Whether a window is listed: a toplevel on screen or hidden, never a parked one. Whether a window is mapped: in the space, or hidden by the policy (minimized, or on another virtual desktop). One a client withdrew, an unmapped X11 window or an xdg toplevel waiting for its next map, is not, so a change to it does not list it again.