By exposing code events and allowing listeners to attach to them, XenForo makes it easy to alter its default functionality with simple callback classes. The API for doing this is well-defined and documented, so modifications made in this way stand a very good chance of remaining backward compatible through future version updates. This video shows me creating a simple add-on that allows us to see how an existing thread would look with over a thousand pages. As usual, it's a large, HD video, so I suggest you view it at its original size by clicking the full-screen gadget in the bottom-right corner of the video. Edit: If for whatever reason you can't view the video here, view it directly on Vimeo (but please leave comments here, not there).