California Code, Code of Civil Procedure - CCP § 166.1

Upon the written request of any party or his or her counsel, or at the judge's discretion, a judge may indicate in any interlocutory order a belief that there is a controlling question of law as to which there are substantial grounds for difference of opinion, appellate resolution of which may materially advance the conclusion of the litigation.  Neither the denial of a request for, nor the objection of another party or counsel to, such a commentary in the interlocutory order, may be grounds for a writ or appeal.