Tex. Penal Code § 2.03: DEFENSE.

(a) A defense to prosecution for an offense in this code is so labeled by the phrase: "It is a defense to prosecution . . . ."

(b) The prosecuting attorney is not required to negate the existence of a defense in the accusation charging commission of the offense.

(c) The issue of the existence of a defense is not submitted to the jury unless evidence is admitted supporting the defense.

(d) If the issue of the existence of a defense is submitted to the jury, the court shall charge that a reasonable doubt on the issue requires that the defendant be acquitted.

(e) A ground of defense in a penal law that is not plainly labeled in accordance with this chapter has the procedural and evidentiary consequences of a defense.

Acts 1973, 63rd Leg., p. 883, ch. 399, Sec. 1, eff. Jan. 1, 1974. Amended by Acts 1993, 73rd Leg., ch. 900, Sec. 1.01, eff. Sept. 1, 1994.