What is CI4's PSR Compliance?

CodeIgniter 4 made significant strides toward PSR compliance compared to CI3. CI4 conforms to: PSR-1 and PSR-12 (coding standards), PSR-3 (Logger Interface — CI4's logger implements Psr\Log\LoggerInterface), PSR-4 (autoloading — full Composer PSR-4 support), PSR-7 (HTTP Messages — CI4's Request and Response classes are inspired by PSR-7 but are not fully compliant; they do not extend PSR-7 interfaces), PSR-11 (Container Interface — partially supported via the Services system). The PSR-7 non-compliance means CI4 does not natively work with PSR-15 middleware packages. However, CI4's Filters achieve the same goal internally. Third-party adapters exist to bridge CI4 with PSR-7 middleware ecosystems if needed. CI4 uses PSR-3 logging fully, so Monolog handlers can be integrated easily.