since 0.2.18 — use App::include() with a public-relative path.

Legacy alias kept for the WordPress showcase and existing user scaffolds. Accepts an absolute path. For paths under the document root, delegates to App::include() (security check + $_SERVER preamble apply). For paths outside (e.g. test fixtures, embedded utilities), passes straight to the shared core so the return contract applies but no security gate fires — matching the historical includeFile() behaviour.