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It tries its superclass, continuing up the hierarchy until the class instance variable is defined or the top level class is reached.

The possible advantage of this approach is that if you create a subclass, and later modify the value of the class instance variable in the superclass, the subclass will see the changed value unless it has been overridden in the subclass itself.

The disadvantage is speed, as lookups can be significantly slower, especially for deep hierarchies.