Cooper v. State
In Cooper v. State 45 S.W.3d 77 (Tex. Crim. App. 2001), this Court held that a plea-bargaining defendant may not appeal the voluntariness of his plea because "such an appeal was forbidden by an act of the legislature in 1977, and that our rules do not, and may not, allow such an appeal." 45 S.W.3d at 77.
In other words, the same amendment that explicitly conferred appellate court jurisdiction over an appeal by a plea-bargaining defendant who either has the trial court's permission or is appealing an adverse ruling on a pretrial motion, denied, by implication, jurisdiction over that defendant's claim of an involuntary plea.
Because the Legislature did not add a third basis for appeal- i.e., the voluntariness of the plea- the appellate court cannot enlarge its jurisdiction to address that claim.
The present situation is precisely the reverse: the Legislature did expressly confer jurisdiction on Texas appellate courts to address the merits of a plea-bargaining defendant's appeal of an adverse ruling on a pretrial motion.
Just as this Court's rules of appellate procedure could not enlarge jurisdiction in Cooper, they cannot limit jurisdiction in these cases.
Cooper dealt solely with the question of whether appellate jurisdiction exists to consider the voluntariness of a plea-bargain, not whether the existing jurisdiction was properly invoked by an adequate notice of appeal.