One we referenced earlier is the implementation of a doubly linked list in the Spl class SplDoublyLinkedList.
The new additions to SPL add some useful functionality to PHP that is easy to use, as well as implementations of data structures, such as doubly linked lists, stacks, heaps, and queues.
Understanding the doubly linked list API will help you develop with this efficient data structure as well as understand the plethora of code in the kernel that utilizes lists.
