What is the scope of an arbitrator's authority?

"An exception to the general rule assigning broad powers to the arbitrators arises when the parties have, in either the contract or an agreed submission to arbitration, explicitly and unambiguously limited those powers. [Citation.] 'The powers of an arbitrator derive from, and are limited by, the agreement to arbitrate. [Citation.] Awards in excess of those powers may, under sections 1286.2 and 1286.6, be corrected or vacated by the court.' [Citation.] The scope of an arbitrator's authority is not so broad as to include an award of remedies 'expressly forbidden by the arbitration agreement or submission.' " (Gueyffier v. Ann Summers, Ltd. (2008) 43 Cal.4th 1179, 1184-1185.)