Cal. Probate Code § 21310

As used in this part: (a) “Contest” means a pleading filed with the court by a beneficiary that would result in a penalty under a no contest clause, if the no contest clause is enforced. (b) “Direct contest” means a contest that alleges the invalidity of a protected instrument or one or more of its terms, based on one or more of the following grounds: (1) Forgery. (2) Lack of due execution. (3) Lack of capacity. (4) Menace, duress, fraud, or undue influence. (5) Revocation of a will pursuant to Section 6120, revocation of a trust pursuant to Section 15401, or revocation of an instrument other than a will or trust pursuant to the procedure for revocation that is provided by statute or by the instrument. (6) Disqualification of a beneficiary under Section 6112, 21350, or 21380. (c) “No contest clause” means a provision in an otherwise valid instrument that, if enforced, would penalize a beneficiary for filing a pleading in any court. (d) “Pleading” means a petition, complaint, cross-complaint, objection, answer, response, or claim. (e) “Protected instrument” means all of the following instruments: (1) The instrument that contains the no contest clause. (2) An instrument that is in existence on the date that the instrument containing the no contest clause is executed and is expressly identified in the no contest clause, either individually or as part of an identifiable class of instruments, as being governed by the no contest clause.