Is a prosecutor prohibited from vouching for the credibility of witnesses or otherwise bolstering the veracity of their testimony by referring to evidence that was not in the record?

"A prosecutor is prohibited from vouching for the credibility of witnesses or otherwise bolstering the veracity of their testimony by referring to evidence outside the record.... However, so long as a prosecutor's assurances regarding the apparent honesty or reliability of prosecution witnesses are based on the `facts of [the] record and the inferences reasonably drawn therefrom, rather than any purported personal knowledge or belief,' her comments cannot be characterized as improper vouching. [Citations.]" (People v. Frye (1998) 18 Cal.4th 894, 971, 77 Cal.Rptr.2d 25, 959 P.2d 183.)