When you unset the reference, you just break the binding between
variable name and variable content. This does not mean that
variable content will be destroyed. For example:
<?php
$a = 1;
$b =& $a;
unset($a);
?>
won't unset $b, just $a.
Again, it might be useful to think about this as analogous to Unix
unlink call.
Returning References
