List of Reserved Words
PHP Manual

Predefined Classes

This section lists standard predefined classes. Miscellaneous extensions define other classes which are described in their reference.

Standard Defined Classes

These classes are defined in the standard set of functions included in the PHP build.

Directory
The class from which dir is instantiated.
stdClass
__PHP_Incomplete_Class

Predefined classes as of PHP 5

These additional predefined classes were introduced in PHP 5.0.0

exception
php_user_filter

Special classes

Following identifiers may not be used as a class name as they have special purpose.

self
parent

List of Reserved Words
PHP Manual