static L<S> web_commonTexts(Collection<WebNode> nodes) {
  if (empty(nodes)) ret ll();
  TreeSet<S> set = null;
  for (WebNode n : nodes) {
    if (set == null) set = new TreeSet(web_texts(n));
    else removeAllBut(set, web_texts(n));
    if (empty(set)) break;
  }
  ret asList(set);
}