Version: (using KDE 4.2.98) Awhile ago, korganizer developers added an extremely useful feature to the to-do view: The category selection dropdown. This easily allows one to filter for items matching one or several categories. A valuable extension to this feature would be to make the selection checkboxes tristate. The goal here would be to allow both positive and negative filtering on categories: For example, the current behavior allows one to find all the items in the "personal" category, but it is not possible to see items *not* in the "personal" category. The tristate checkboxes would presumably need custom icons, as the standard tristate icons don't accurately capture the ideas of positive and negative filtering.