public void backtrack(RuleEvaluation e) {
            backtrackPosition(e);

            // Is this check masking errors?
            if (e.referencedMatches().size()>referencedMatchCount)
                e.referencedMatches().subList(referencedMatchCount,
                        e.referencedMatches().size())
                        .clear();
            // Is this check masking errors?
            if (e.nonreferencedMatches().size()>nonreferencedMatchCount)
                e.nonreferencedMatches().subList(nonreferencedMatchCount,
                        e.nonreferencedMatches().size())
                        .clear();
        }
Backtrack to the evaluation state at the point where this choicepoint were instantiated
container-search/src/main/java/com/yahoo/prelude/semantics/engine/Choicepoint.java