ClassLoader

ClassLoader implements an PSR-0 class loader.

See https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-0.md

$loader = new ClassLoader();

// register classes with namespaces
$loader->addPrefix('Symfony\Component', __DIR__.'/component');
$loader->addPrefix('Symfony',           __DIR__.'/framework');

// activate the autoloader
$loader->register();

// to enable searching the include path (e.g. for PEAR packages)
$loader->setUseIncludePath(true);

In this example, if you try to use a class in the Symfony\Component namespace or one of its children (Symfony\Component\Console for instance), the autoloader will first look for the class under the component/ directory, and it will then fallback to the framework/ directory if not found before giving up.