1. by a citizen against his or her own state. Hans v. Louisiana (1890)
2. covers Fed question suits, not just diversity suits.
3. that a state may not  be sued even by its own citizens, and may not be sued even in a case raising a Fed question—is now held to be a core constitutional limitation on Fed judicial power.
4. applies not only to suits “at law,” but also to suits “at equity”. Thus a private citizen cannot sue to have a state enjoined or ordered to do something, any more than she can sue to recover damages