// use "*" as wildcard
// may return null, and returned list is "volatile" (only valid as long as the index is not changed)
static LLS positionalTokenIndex2_filter(PositionalTokenIndex2 idx, LS tok) {
  PositionalTokenIndex idx2 = idx.indexForTokenCount(l(tok)/2);
  if (idx2 == null) null;
  ret positionalTokenIndex_filter(idx2, tok);
}