// In the index.php file require_once 'vendor/autoload.php'; use Slim\Factory\AppFactory; $app = AppFactory::create(); $app->setBasePath('/myapp'); // Define your routes here $app->get('/', function ($request, $response, $args) { $response->getBody()->write('Hello World!'); return $response; }); $app->run();In this example, we are using the Slim framework to create a web application. We set the base URL for the application using `$app->setBasePath('/myapp')`. This means that all routes for the application will be prefixed with `/myapp`. This function is part of the Slim framework, which is a package/library for building web applications in PHP.