public class ComparisonPredicateIndex.RuleIndex
A class to contain a list of rules
indexed against a set of atomic value match keys.
The implication is that all the rules have a common base and LHS comparison predicate,
such as b[@class=...] and are indexed against the RHS values found.
The rule lists found should be in precedence order and each rule may have
additional qualifications, such as an ancestral qualification.