...You can install the Annotation component with composer. The access to the annotations happens by reflection of the class containing them. There are multiple reader-classes implementing the Doctrine\Common\Annotations\Reader interface, that can access the annotations of a class. A common one is Doctrine\Common\Annotations\AnnotationReader. Note that AnnotationRegistry::registerLoader('class_exists') only works if you already have an autoloader configured (i.e. composer autoloader). Otherwise, please take a look to the other annotation autoload mechanisms.