5.2.2 Slot inheritance

A class inherits the slots of its superclasses, and can define more slots if they are needed. For example, the <time-of-day> and <time-offset> classes inherit the total-seconds slot from their superclass, <time>. A class inherits the slot options from its superclasses as well. A class cannot remove or replace any slots defined by its superclasses. It is an error for a class to define a slot with the same name as a slot inherited from one of that class's superclasses.