What is the legal basis for an award of attorney fees de novo?

"`On appeal this court reviews a determination of the legal basis for an award of attorney fees de novo as a question of law.' [Citation.]" (Butler-Rupp v. Lourdeaux (2007) 154 Cal.App.4th 918, 923.) Under Code of Civil Procedure section 1032, subdivision (4)(b), "a prevailing party is entitled as a matter of right to recover costs in any action or proceeding." Recoverable costs include attorney's fees, when authorized by contract, statute, or law. (Code Civ. Proc., 1033.5, subd. (a)(10).) Civil Code section 1717 provides, in pertinent part: