Many developers writing object-oriented applications create one PHP source file per-class definition. One of the biggest annoyances is having to write a long list of needed includes at the beginning of each script (one for each class). In PHP 5, this is no longer necessary. You may define an __autoload function which is automatically called in case you are trying to use a class which hasn't been defined yet. By calling this function the scripting engine is given a last chance to load the class before PHP fails with an error. Exceptions thrown in __autoload function cannot be caught in the catch block and results in a fatal error. Autoloading is not available if using PHP in CLI interactive mode. If the class name is used e.g. in call_user_func then it can contain some dangerous characters such as ../. It is recommended to not use the user-input in such functions or at least verify the input in __autoload. This example attempts to load the classes MyClass1 and MyClass2 from the files MyClass1.php and MyClass2.php respectively. ]]>