(PHP 5 >= 5.3.0, PHP 7) Check whether the queue contains more nodes

(PHP 5 >= 5.3.0, PHP 7) Peeks at the node from the top of the queue

(PHP 5 >= 5.3.0, PHP 7) Constructs a new empty queue

(PHP 5 >= 5.3.0, PHP 7) Extracts a node from top of the heap and sift up.

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

(PHP 5 >= 5.3.0, PHP 7) Return current node index

(PHP 5 >= 5.3.0, PHP 7) Sets the mode of extraction

(PHP 5 >= 5.3.0, PHP 7) Recover from the corrupted state and allow further actions on the queue.

(PHP 5 >= 5.3.0, PHP 7) Rewind iterator back to the start (no-op)

(PHP 5 >= 5.3.0, PHP 7) Inserts an element in the queue by sifting it up.