(1) “Attack” means any action or series of actions taken by an enemy of the United States resulting in substantial damage or injury to persons or property in this Commonwealth, whether through sabotage, bombs, missiles, shellfire, or atomic, radiological, chemical, bacteriological or biological means or other weapons or methods.

(2) “Unavailable” means absent from the place of session (other than on official business of the General Assembly), or unable, for physical, mental or legal reasons, to exercise the powers and discharge the duties of a legislator, whether or not such absence or inability would give rise to a vacancy under existing constitutional or statutory provisions.

(3) “Legislator” means a member of the General Assembly of the Commonwealth of Pennsylvania.

(4) “Emergency interim successor” means (a) a legislator elected in the manner hereinafter prescribed for temporary succession to the powers and duties but not to the office of Speaker of the House of Representatives or President pro tempore of the Senate, or (b) a person appointed in the manner hereinafter prescribed for temporary succession to the powers and duties but not the office of a legislator.