layout_manager -> initialise- Initialise an abstract instance. Subclasses normally extend this with
their own setup.
layout_manager -> attach:graphical- Attach the manager to a device, taking responsibility for the layout of
the device's graphicals.
layout_manager -> detach- Detach from the current device.
layout_manager -> unlink- Called when the manager is destroyed: cleanly detach from
layout_manager
<-device.
layout_manager -> compute- Virtual method: recompute the layout. Subclasses override.
layout_manager -> compute_bounding_box- Virtual method: compute the union bounding box of the laid-out
graphicals. The default implementation fails (no contribution).
layout_manager -> RedrawArea:area- Paint background objects for the indicated area. The default
implementation succeeds without drawing.
