Imagine a user issues one query and inspects the clusters generated for it. Then the user issues another query and does the same, but then clicks the "Back" button to once again see the clusters returned for the previous query. In the current web application, the user will be presented with the initial state of the cluster tree (All Topics selected, only the first few clusters visible), which is kind of annoying. Ideally, when the user presses "Back", he would see the previous cluster tree just he left it (i.e. with the last selected cluster). It seems to me that this can be implemented using the standard Ajax history management trick, i.e. by encoding the last selected cluster as the anchor (#sth) part of the main url. With this approach not only we would be able to honor the cluster selection history, but also we could make the cluster selection bookmarkable.