adding index to cookie

[niche]

Turns out that this code will add an index to a cookie, but I can't find any documentation on this notation except for something similar, in example 3, in the manual. I'd appreciate any comments or thoughts on this snippet:

<?php$last = $_COOKIE['last'] . ', YEP';setcookie("last", $last);?> 

Edited December 27, 2013 by niche