Defines and implements a Doubly Linked List Node Abstract Data Structure and DLLNode class. A Node subclass. A DLLNode has a data attribute, a front attribute, and a back attribute. There is a DLLNode class and a DLLNodeHelper module. The class and the module contain eleven methods. Six methods are public DLLNode instance methods, three are private DLLNode instance methods, and two are helper methods.