This document describes the concept of headers as regards to doubly linked lists.
A header forms the anchor point for a doubly linked list. In common with the elements of the list, the header includes a link object as a component.
The header includes the following functionality:
allows elements to be added to the start and end of a doubly linked list, but not to the middle.
tests if an element is at the start or end of a list.
returns pointers to elements at the start or the end of a list.
A header is an instance of the templated class TDblQue<class
T>.