yii2/docs/internals/autoloader.md

Yii2 class loader

Yii 2 class loader is PSR-0 compliant. That means it can handle most of the PHP libraries and frameworks out there.

In order to autoload a library you need to set a root alias for it.

PEAR-style libraries

\Yii::setAlias('@Twig', '@app/vendors/Twig');

References

• BaseYii::autoload