static PTElement ai_scanParseTreeForWord(PTElement e, S word) {
  if (e == null) null;
  if (eqic(e.text(), word)) ret e;
  for (PTElement child : unnull(e.children)) {
    PTElement x = ai_scanParseTreeForWord(child, word);
    if (x != null) ret x;
  }
  null;
}