Historically, web applications were based on a strict request-response paradigm. The client sends actions and possibly some data, the server responds with a whole HTML page reflecting the new state. With so-called Web 2.0, the pages became more dynamic and many user actions are now processed with client-side scripts. Pages are not reloaded as a whole anymore but partial updates to their DOM are made as necessary.
TDI (Turbocharged DOM Infusion) brings a novel approach which is a sort of compromise between the old plain request-response paradigm and individual micro-requests. With TDI, user actions are still sent to the server in one request. The server performs the action and then it decides what portions of the page should be updated and how. These updates are embedded into one XML response containing fragments of HTML. It is supposed that these fragments are generated by the very same templates as the original page.