“Intervention is the procedure whereby someone not previously served as a party to an action (or ordered joined as a party) may nevertheless become a party. An intervention takes place when the court grants leave to a nonparty to join the plaintiff in claiming what is sought by the complaint; or to unite with the defendant in resisting the plaintiff’s claims; or to demand anything adverse to both parties.”
[California Practice Guide: Civil Procedure Before Trial [citations to primary sources omitted]]
