PSR-4 Meta Document 1. Summary The purpose is to specify the rules for an interoperable PHP autoloader that maps namespaces to file system paths, and that can co-exist with any other SPL registered autoloader. This would be an addition to, not a replacement for, PSR-0. 2. Why Bother? History of PSR-0 The PSR-0 class naming and autoloading standard rose out of the broad acceptance of the Horde/PEAR