§ 428.20.Joinder of Person As Cross-Complainant Or Cross- Defendant

Section 428.20 extends California's general rules on joinder of parties into the cross-complaint context. When a party files a cross-complaint under § 428.10, it may join any person as a cross-complainant or cross-defendant — regardless of whether that person is already involved in the case — as long as joining that person would have been permitted under the ordinary statutes governing joinder of parties if the cross-complaint had instead been filed as its own independent lawsuit.

The test the section sets is a hypothetical one: imagine the cross-complaint stood alone as a new action, and ask whether the party-joinder rules would allow bringing in the person in question. If yes, that person can be joined in the cross-complaint exactly as they could have been joined in a freestanding suit.

This mirrors § 428.10(b)'s substantive test for what claims a cross-complaint may assert against a non-party by tying the procedural question — who can be brought into the case — to the same body of law that governs ordinary party joinder generally, rather than creating a separate, cross-complaint-specific standard.