svoid test_positionalTokenIndex2_filter() {
  PositionalTokenIndex2 idx = positionalTokenIndex2_wordTok(tlft([[
    you are here
    what is this
    hello world
    hello you
    hello my friend
  ]]));
  assertEqualsVerbose(ll("you are here"), map join(
    positionalTokenIndex2_filter(idx, "you * *")));
  assertEqualsVerbose(ll("hello world"), map join(
    positionalTokenIndex2_filter(idx, "* world")));
  // index should preserve original order
  assertEqualsVerbose(ll("hello world", "hello you"), map join(positionalTokenIndex2_filter("hello *"));
  assertEqualsVerbose(ll("what is this"), map join(positionalTokenIndex2_filter("* is this")));
  assertEqualsVerbose(ll(), unnull(map join(positionalTokenIndex2_filter("* * is"))));
}