static Concept conceptFromMatches(Class<? extends Concept> cClass, Matches m) {
  Concept c = cnew(cClass);
  S order = toStringOpt(getOpt(cClass, "_fieldOrder"));
  L<S> fields;
  if (order != null)
    fields = splitAtSpace(order);
  else
    fields = asList(asTreeSet(conceptFields(c)));
  if (l(fields) != l(m.m))
    fail(struct(fields) + " / " + struct(m.m));
  for i over fields:
    cset(c, fields.get(i), parseToOptions(m.unq(i)));
  ret c;
}