Cover; Title; Copyright; Contents; Lists of figures; Acknowledgements; 1 Discourse topic: towards understanding topical actions on Timelines; 2 Introducing a topic: sample analysis of introducing a topic; 3 Continuing a topic: sample analysis of continuing a topic; 4 Changing a topic: sample analysis of changing a topic; 5 Digressing from a topic: sample analysis of digressing from a topic; 6 Shifting a topic: sample analysis of shifting a topic; 7 Closing a topic: sample analysis of closing a topic; Index