(a) Reputation or opinion. In all cases in which evidence of character or a trait
of character of a person is admissible, proof may be made by testimony as to
reputation or by testimony in the form of an opinion. On cross-examination,
inquiry is allowable into relevant specific instances of conduct.
(b) Specific instances of conduct. In cases in which character or a trait of
character of a person is an essential element of a charge, claim, or defense, or
pursuant to Rule 404(c), proof may also be made of specific instances of that