static S ai_makeSubjectAction(S text, IntRange r) {
  if (r == null) null;
  int i = trimIndexRight(text, r.start);
  int j = trimIndexLeft(text, r.end);
  ret j <= i ? null : "subject=" + quote(substring(text, i, j)) + " (" + i + "/" + (j-i) + ")";
}