Description:
------------
It is easy to extend the array_walk_recursive function to be more useful in non-
trivial situations which require information about depth & path in the array 
structure the cursor is in, by adding an optional 4th parameter.  This would 
eliminate the need for MANY user-written depth first search traversal recursive 
functions.  Which consequently makes PHP a more attractive language for people 
who 
fear recursion, but need a tree walk function which provides contextual 
information to the callback.

bool array_walk_recursive ( array &$input , callback $funcname [, mixed 
$userdata 
] [, array $state] )

where $state is a data dictionary having any number of context relevant data 
e.g. 
the depth of recursion (int), and the keys traversed to arrive at this node (a 
1-
dimensional list array of string).

This enhancement is low risk: it would not break backward-compatibility.
This enhancement is high reward: it would make Xpath-like operations more 
approachable to the average developer.
This enhancement would simplify user code: which tends to increase security for 
websites.

Test script:
---------------
var $state = Array(
        $depth => 0
        ,$path => Array()
);

Expected result:
----------------
N/A

Actual result:
--------------
N/A