The document discusses progressive enhancement with JavaScript and Ajax. It defines progressive enhancement as testing for support of different technologies like JavaScript, DOM, and objects, and providing alternative interfaces when something is not supported. It recommends testing for dependencies before using them, and separating interfaces from styles using CSS for flexibility. While CSS-only solutions seem appealing, JavaScript is more powerful and reliable for building complex, accessible interfaces. The key is enhancing interfaces thoughtfully to improve the user experience, not just for the sake of enhancement.