(PHP 5 >= 5.3.0)
SplMinHeap::compare — Compare elements in order to place them correctly in the heap while sifting up.
The value of the first node being compared.
The value of the second node being compared.
Result of the comparison, positive integer if value1 is lower than value2, 0 if they are equal, negative integer otherwise.
Having multiple elements with the same value in a Heap is not recommended. They will end up in an arbitrary relative position.