Every body whose parentId names no body in the system. Position
resolution can't follow the chain any further, so the body is placed
relative to the system's origin instead — silently, until this check
(belts already had the equivalent — see findInvalidBelts).
Every body whose
parentIdnames no body in the system. Position resolution can't follow the chain any further, so the body is placed relative to the system's origin instead — silently, until this check (belts already had the equivalent — see findInvalidBelts).