(PHP 5 >= 5.3.0, PHP 7) Returns whether the requested index exists

(PHP 5 >= 5.1.0, PHP 7) Seek to specified line

(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 >= 5.1.0, PHP 7) Alias of

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

(PHP 5 >= 5.0.0, PHP 7) Unsets the value at the specified index

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

(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) Compare elements in order to place them correctly in the heap while sifting up.