Is Jury Instruction on ''Reliability'' of Evidence Legal ?

In Zani v. State, 758 S.W.2d 233 (Tex. Crim. App. 1988), the court addressed issues arising from the use of hypnotically enhanced testimony. Among other things, the court held that the trial court properly refused to give a cautionary instruction against placing undue reliance on such testimony. See id. at 245. "Such an instruction, though seemingly neutral on its face, has the effect nonetheless of singling out evidence and inviting jurors to pay it particular attention." Id. Citing Zani, the court held in Matamoros v. State, 901 S.W.2d 470, 477 (Tex. Crim. App. 1995), that an instruction concerning the reliability of DNA evidence would constitute an impermissible comment on the weight of the evidence.