This document discusses migrating from AngularJS to Angular while maintaining support for legacy AngularJS code and routes. It covers using UI-Router for routing in a hybrid app, the ngUpgrade module for integrating Angular and AngularJS components, and a sample app that demonstrates how to migrate routes, components, and connect the two frameworks. Key steps in the migration include preparing the AngularJS app, configuring UI-Router, bootstrapping both frameworks, and using ngUpgrade to share components between the frameworks.