Guides classic CodeIgniter 2.x/3.x applications (the application/ directory, bcit-ci/CodeIgniter, no PHP namespaces) - a fundamentally different framework generation from CodeIgniter 4. Use when working in a codebase with an application/ directory and CI_VERSION below 4, extending MY_Controller or a *_model class, adding a route, or reviewing code that assumes CI4-style namespaces or DI.
