Just about anything you could think to do with a string in PHP probably already has a dedicated function.
strtolower
(PHP 3, PHP 4 )
strtolower -- Make a string lowercase
Description
string strtolower ( string str)
Returns string with all alphabetic characters converted to lowercase.
Note that 'alphabetic' is determined by the current locale. This means that in i.e. the default "C" locale, characters such as umlaut-A (Ä) will not be converted.
EDIT: damn, I'm too slow!!
PHP.net, don't do code without it™ 😃