What is the burden of proving a defendant's mental competence?

"As to who has the burden of proof on the question of the defendant's mental competence, section 1369, subdivision (f), states in part: 'It shall be presumed that the defendant is mentally competent unless it is proved by a preponderance of the evidence that the defendant is mentally incompetent.' Thus, under California law, when a trial court 'prior to judgment' ( 1368, subd. (a)) suspends criminal proceedings and holds a mental competency hearing, it is the defendant who bears the burden of establishing lack of competence ( 1369, subd. (f); [citation.]" (People v. Ary (2011) 51 Cal.4th 510, 517518 (Ary).)