In de XPage blog staat een artikel van Peter Presnell over het NotesXspDocument:
When using Notes Classic to develop applications for the Notes client most of your code is executed on the client with LotusScript able to maintain a continuous exchange with the server. With the Web model used by XPages it is either not possible or not practical for the Domino server to keep the NotesDocument objects open for the life of a transaction. This has given rise to the creation of a new NotesXspDocument object which acts as a buffer between Web Page and the NotesDocument objects holding the data. The NotesDocument object only has a life as long as a single trip to the server. The NotesXspDocument however stays with the XPage as it travels back and forward between the server and the client.
Het artikel legt verder de werking van de XPages omgeving in detail uit. Zeer interessant dus.