How can a court interpret a contract to rule on a demurrer?

In Hervey v. Mercury Casualty Co. (2010) 185 Cal.App.4th 954, 962 (Hervey), the court explained when a court may interpret a contract to rule on a demurrer: " 'When the complaint fails to allege that the terms of the contract have any special meaning, the court can construe the language of the document on its face to determine whether as a matter of law the contract is reasonably subject to a construction sufficient to sustain a cause of action in response to a demurrer. However, when the plaintiff alleges a meaning to the document that is reasonable in light of its terms, the court cannot grant a demurrer but must permit the admission of extrinsic evidence regarding the meaning of the document as intended by the parties.' " The interpretation of a written contract is subject to de novo review, unless interpretation turns on the credibility of extrinsic evidence. (In re Electric Refund Cases (2010) 184 Cal.App.4th 1490, 1500.)