I want to be able to exclude certain tags from reports

I find the combination of Taskwarrior and Timewarrior really great, but there is a minor inconvenience in the way TImewarrior works. In Taskwarrior--and that doesn't seem to be properly documented--one can use exclude filters with something like `-tag` to filter out tasks that have a particular tag. The same functionality doesn't seem to be supported in Timewarrior, which instead treats `-` in `-tag` as part of the tag name.

Use case: I use my desktop computer mainly for work, but from time to time I do some tasks that are not related to work. Those tasks are a relatively low in number and I tag them `private`. I would like to be able to exclude them from the reports. Currently, the only options are to tag all other tasks as `work` and then use `timew summary work` or to manually subtract the time for private tasks from the totals, which doesn't work for reports. It would be easier if I could just do something like `timew month -private`.