Manual:Hooks/UserGroupsChanged

Details

 * $user: User whose groups changed
 * $added: Groups added
 * $removed: Groups removed
 * $performer: User who performed the change, false if via autopromotion
 * $reason (added in MW 1.28): Reason/log comment for the change, or false if via autopromotion
 * $oldUGMs (added in MW 1.31): old user group memberships (as returned by )
 * $newUGMs (added in MW 1.31): new user group memberships