These are [boolean chart parameters](https://wiki.mozilla.org/Bugzilla:REST_API:Search#Boolean_Charts). They're used by [harthur](https://github.com/harthur), who wrote [bz.js](https://github.com/harthur/bz.js), in her [Bugzilla Todos](http://bugmotodo.org/) tool. We're modeling the categories after those in her tool, so I figured it would be good to use her parameters.