Mix-in class
From IFWiki
In TADS 3, a mix-in class is any class that cannot be used by itself, but must be used in conjunction with another class. Examples include Lockable, BagOfHolding, and LockableWithKey.
In TADS 3, a mix-in class is any class that cannot be used by itself, but must be used in conjunction with another class. Examples include Lockable, BagOfHolding, and LockableWithKey.