Description:
------------
In http://ua2.php.net/unset nothing said about how work unset() on local variables (PASSED BY REFERENCE or NOT).

unset() always "destroy" variables in local area. See code 1.

May be would be good to write, that for variable PASSED BY REFERENCE we can use operation = null to unset variable. See code 2.

Reproduce code:
---------------
<?php
function a() {
$foo = 'ok';
b($foo);
var_dump($foo);
}
function b(&$foo) {
$foo = 'not ok';
unset($foo);
}
a();
?>

<?php
function a() {
$foo = 'ok';
b($foo);
var_dump($foo);
}
function b(&$foo) {
$foo = 'not ok';
$foo=null;
}
a();
var_dump($b);
?>

Expected result:
----------------
For code 1. 
One of tree:

1. 'ok'
2. 'not ok'
3. variable $foo is null (not setted)

For code 2.

NULL NULL

Actual result:
--------------
'not ok'

NULL NULL