This example dissects the source code of Express 4.2.0, a Node.js web framework, showing how its API is structured and executed. It maps the request-handling pipeline, including middleware chains and route registration through methods like `app.use` and `app.get`. The visualization outlines the framework’s file structure and the internals of the Router component, including middleware stack data and initialization logic. It references specific code from `application.js`, `router/index.js`, and middleware modules such as `query` and `expressInit`.