(A) For the purpose of this subchapter, the following definition shall apply unless the context clearly indicates or requires a different meaning.
AFFIRMATIVE DEFENSE. Unless the village’s evidence raises the issue involving the alleged defense, the defendant, to raise the issue, must prevent some evidence thereon.
(B) If the issue involved in an affirmative defense is raised, then the village must sustain the burden of proving the defendant guilty beyond a reasonable doubt as to that issue together with all the other elements of the offense.
(ILCS Chapter 720, Act 5, § 3-2) (1981 Code, § 42.03, 3-2)