Thats right, you effectively chain together functionality of multiple autoloads. So it checks in method a first, then in method b, and all the way through the chain until it either finds a valid condition (such as a class to load), or fails to find it.
This is why the namespaces are so convenient, its a matter of putting it to the root directory and autoloading it:
The use is automatically invoked to use the filepath as the namespace path, so you never need to issue an include/require again for a class to load. Too bad your PHP version is < 5.3.
set_include_path(get_include_path() . PATH_SEPARATOR . realpath(__DIR__ . "/../"));