The document discusses building user interfaces with Dart. It begins by comparing building UIs with JavaScript, Java, and GWT. It then shows how to build a table component programmatically in GWT. Next, it demonstrates how to build the same table in Dart using fewer lines of code. The document proceeds to provide an overview of Dart and its ecosystem. It discusses building object hierarchies and rendering them to the DOM in an "old-fashioned" way using strings. It introduces the idea of reusable components and recursive patterns. It demonstrates implementing a reusable Tree component in Dart using accessors and configurations.