static PositionalTokenIndex test_PositionalTokenIndex() {
  new PositionalTokenIndex idx;
  idx.addAll(map wordTok(tlft([[
    you are here
    what is this
    hello world
    hello you
  ]])));
  printStruct(idx);
  assertEqualsVerbose(ll("you are here"), map join(idx.byToken(0, "you")));
  ret idx;
}