11.1. Making your objects KVC-compliant

KVC is all about conventions. In order for KVC to determine which setter or getter message should be sent to access a given key, you must conform to a specific set of rules. If you attempt to use a non-KVC-compliant object with KVC, you’ll get an exception similar to the following at runtime:

[<CTRentalProperty 0x1322> valueForUndefinedKey:] this class is not key value
     coding-compliant for the key age