(PHP 5 >= 5.3.0, PHP 7) Checks whether the doubly linked list is empty.

(PHP 5 >= 5.1.2, PHP 7) Tells if the file is a link

(PHP 5 >= 5.1.0, PHP 7) Get the current value

(PHP 5 >= 5.1.0, PHP 7) End children public

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

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

(PHP 5 >= 5.2.2, PHP 7) Gets the target of a link

(PHP 5 >= 5.3.0, PHP 7) Detaches an iterator

(PHP 5 >= 5.3.0, PHP 7) Compare elements in order to place them correctly in the heap while sifting up.

(PHP 5 >= 5.1.0, PHP 7) Get the inner iterator