User Criteria Extended
Heavily extends the range of available user criteria by adding opposite criteria for most existing criteria, along with a whole range of new criteria that can mostly be derived from the existing XenForo criteria setup with no additional calculation effort.
When XenForo needs to test something (user/page/post...) against some user-selected conditions (criteria), it uses the Criteria system.
Some places, where the Criteria system is used:
Addons can also use this system.