What constitutes substantial evidence of incompetence in a criminal case?

" 'Evidence of incompetence may emanate from several sources, including the defendant's demeanor, irrational behavior, and prior mental evaluations.' " (People v. Lewis (2008) 43 Cal.4th 415, 524 (Lewis).) Among other things, "[s]ubstantial evidence of incompetence exists when a qualified mental health expert who has examined the defendant states under oath, and ' " 'with particularity,' " ' a professional opinion that because of mental illness, the defendant is incapable of understanding the purpose or nature of the criminal proceedings against him, or of cooperating with counsel. [Citations] [] The defendant's demeanor and irrational behavior may also, in proper circumstances, constitute substantial evidence of incompetence. [] Counsel's assertion of a belief in a client's incompetence is entitled to some weight. But unless the court itself has declared a doubt as to the defendant's competence, and has asked for counsel's opinion on the subject, counsel's assertion that his or her client is or may be incompetent does not, in the absence of substantial evidence to that effect, require the court to hold a competency hearing." (Mai, supra, 57 Cal.4th at pp. 1032-1033.)

In deciding whether the trial court was required to hold a competency hearing, our inquiry on appeal is whether a review of the record reveals "a showing of 'incompetence' that is 'substantial' as a matter of law." (Mai, supra, 57 Cal.4th at p. 1033.) In all other instances, where "we cannot say as a matter of law that the evidence raised a reasonable doubt as to defendant's mental competence" (People v. Danielson (1992) 3 Cal.4th 691,

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727), the trial court's decision whether or not to hold a competency hearing "is entitled to great deference" and will not be disturbed absent an abuse of discretion. (Mai, at p. 1033; see also People v. Welch (1999) 20 Cal.4th 701, 742 (Welch) ["When the evidence casting doubt on an accused's present competence is less than substantial" it is "within the discretion of the trial judge whether to order a competence hearing"].)