Is the PHP implementation of a Heap really a full implementation?

When I read this article, <http://en.wikipedia.org/wiki/Heap_%28data_structure%29>, I get the idea that a child node has a specific parent, and that a parent has specific children.

When I look at the example in the PHP documentation however, <http://au.php.net/manual/en/class.splheap.php>, it seems that child nodes all share the same 'level', but the specific parent/child information is not important.

For example, which node is the parent for each of the three nodes who are ranked 10th in the PHP example?

In my application, when a user selects 'node 156', I need to know who its children are so that I can pay them each a visit. (I could make their identities 'node 1561', 'node 1562', etc, so the relationship is obvious).

Is the PHP Heap implementation incomplete? Should I forget the Spl class and go my own way? Or am I missing something about how heaps should operate? Or perhaps I should be looking at a particular heap variant?

Thanks heaps!