does php4 have language level classes

all, php5 has language-level classes that ship w/ many of the extensions. PDO <http://www.php.net/manual/en/ref.pdo.php> is a primary example. recently, through a sort-of round-about way, i have been working w/ the serialize function, which lead me to discover It is not possible to serialize PHP built-in objects. From the page <http://us2.php.net/manual/en/function.serialize.php> on the serialize function. What i would like to know is; are there any language-level classes in the core or extensions of PHP4, or does it just allow user level classes to be defined and thats it? thanks, -nathan