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Subject: Unsetting loop variables at the end of the loop
From: mwacker@cornellsun.com (Mike Wacker)

PHP's documentation for foreach states that if you iterate by reference 
[foreach ($ii as &$i) ...], you should unset $i after the loop.  $i 
still points to the last element of the array - updating $i or reusing 
it will update the last element of the array.

In short, why doesn't PHP automatically unset $i after the loop?  I 
can't think of too many cases where you would want to hold on to that 
reference after you exit the loop, but I can think of a lot of scenarios 
where a user could accidentally tamper the array by using $i in a 
different context later on (especially since loop variable names often 
are reused).