Since this is only mentioned in the footnote of the output of one of the examples, I feel it should be spelled out:
* THIS FUNCTION ONLY VISITS LEAF NODES *
That is to say that if you have a tree of arrays with subarrays of subarrays, only the plain values at the leaves of the tree will be visited by the callback function. The callback function isn't ever called for a nodes in the tree that subnodes (i.e., a subarray). This has the effect as to make this function unusable for most practical situations.
