Upon an appeal pursuant to Section 904.1 or 904.2, the reviewing court may review the verdict or decision and any intermediate ruling, proceeding, order or decision which involves the merits or necessarily affects the judgment or order appealed from or which substantially affects the rights of a party, including, on any appeal from the judgment, any order on motion for a new trial, and may affirm, reverse or modify any judgment or order appealed from and may direct the proper judgment or order to be entered, and may, if necessary or proper, direct a new trial or further proceedings to be had. The respondent, or party in whose favor the judgment was given, may, without appealing from such judgment, request the reviewing court to and it may review any of the foregoing matters for the purpose of determining whether or not the appellant was prejudiced by the error or errors upon which he relies for reversal or modification of the judgment from which the appeal is taken. The provisions of this section do not authorize the reviewing court to review any decision or order from which an appeal might have been taken.
Ca. Civ. Proc. Code § 906