GWT includes both a tool set (e.g. hosted mode, compiler) and a set of libraries (e.g. widgets, RPC, XML, JSON). It has always been a design principle that GWT users should be able to write and use their own libraries. Indeed, you could totally replace all of the GWT libraries if you chose to. In this session, Bruce Johnson explains why you probably wouldn't want to do that by pointing out the breadth of the GWT libraries and the sometimes subtle design decisions, and the resulting benefits that underlie them.