code: @Override
      public Collection<String> findBySurnamesBeginWith(final FinderObject owner,
              final String beginsWith) {
          final Root root = (Root) owner;
          final RootVisitor visitor = new RootVisitor();
          root.accept(visitor);
          final Set<String> matches = new TreeSet<>();
          for (final Person person : visitor.getPersons()) {
              final String personSurname = person.getSurname();
              if (personSurname.startsWith(beginsWith)) {
                  matches.add(personSurname);
              }
          }
          return matches;
      }
docs: {@inheritDoc}