// i must point at the (possibly imaginary) opening bracket ("{")

// index returned is index of closing bracket + 1 (or l(tok))

// version using iterator (much faster than v1!)

static int tok_findEndOfBlock_IContentsIndexedList2_v2(IContentsIndexedList2<S> tok, int i) {

  int n = l(tok);

  // find opening & closing brackets after start index

  HasIndex start = new(i);

  TreeSet<HasIndex> openers = tok.indicesOf_treeSetOfHasIndex("{");

  Iterator<HasIndex> iOpener = openers?.tailSet(start, false).iterator();

  TreeSet<HasIndex> closers = tok.indicesOf_treeSetOfHasIndex("}");

  Iterator<HasIndex> iCloser = closers?.tailSet(start, false).iterator();

  // now step through both sets

  int level = 1;

  HasIndex nextOpener = iOpener != null && iOpener.hasNext() ? iOpener.next() : null;

  HasIndex nextCloser = iCloser != null && iCloser.hasNext() ? iCloser.next() : null;

  while true {

    if (nextCloser == null) ret n; // block isn't closed

    if (nextOpener != null && nextOpener.idx < nextCloser.idx) {

      // process opener

      ++level;

      nextOpener = iOpener.hasNext() ? iOpener.next() : null;

    } else {

      // process closer

      if (--level == 0)

        ret nextCloser.idx+1;

      nextCloser = iCloser.hasNext() ? iCloser.next() : null;

    }

  }

}