(PHP 5 >= 5.3.0, PHP 7) Check whether the doubly linked list contains more nodes

(PHP 5 >= 5.3.0, PHP 7) Returns the value at the specified $index

(PHP 5 >= 5.3.0, PHP 7) Prepends the doubly linked list with an element

(PHP 5 >= 5.3.0, PHP 7) Pushes an element at the end of the doubly linked list

(PHP 5 >= 5.3.0, PHP 7) Shifts a node from the beginning of the doubly linked list

(PHP 5 >= 5.4.0, PHP 7) Serializes the storage

(PHP 5 >= 5.3.0, PHP 7) Move to previous entry

(PHP 5 >= 5.3.0, PHP 7) Move to next entry

(PHP 5 >= 5.3.0, PHP 7) Unsets the value at the specified $index

(PHP 5 >= 5.3.0, PHP 7) Counts the number of elements in the doubly linked list.