SplHeap::compare Compare elements in order to place them correctly in the heap while sifting up. &reftitle.description; abstract intSplHeap::compare mixedvalue1 mixedvalue2 Compare value1 with value2. Throwing exceptions in SplHeap::compare can corrupt the Heap and place it in a blocked state. You can unblock it by calling SplHeap::recoverFromCorruption. However, some elements might not be placed correctly and it may hence break the heap-property. &reftitle.parameters; value1 The value of the first node being compared. value2 The value of the second node being compared. &reftitle.returnvalues; Result of the comparison, positive integer if value1 is greater 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.