code: public static Predicate<Tuple2<Context<?>, Boolean>> onlyMismatches() {
          return new Predicate<Tuple2<Context<?>, Boolean>>() {
              public boolean apply(Tuple2<Context<?>, Boolean> tuple) {
                  return !tuple.b;
              }
          };
      }
docs: A predicate usable as a filter (element) of a {@link org.parboiled.parserunners.TracingParseRunner}.
  Enables printing of rule tracing log messages for all mismatched rules.
  
  @return a predicate