PSR-4 Autoloading Standard

When to use

• The user reports a class that loads on macOS but fails to load on Linux, a classic PSR-4 case-sensitivity problem.
• The user is moving a library off the deprecated PSR-0 standard to PSR-4.
• The user is structuring a package's classes so any PSR-4 autoloader can resolve them.
• The user needs to know how a fully qualified class name is translated to a file path under PSR-4, or why a class fails to load.

When NOT to use

• Do not apply PSR-4 to legacy classes that have no namespace; use a classmap for that code instead.
• Do not use PSR-4 to load procedural scripts, templates, or files that declare no class.

Core guidance