Texas Penal Code - PENAL § 2.02. Exception

(a) An exception to an offense in this code is so labeled by the phrase: “It is an exception to the application of . . . .”

(b) The prosecuting attorney must negate the existence of an exception in the accusation charging commission of the offense and prove beyond a reasonable doubt that the defendant or defendant's conduct does not fall within the exception.

(c) This section does not affect exceptions applicable to offenses enacted prior to the effective date of this code.