code: function push_(array, position, element) {
      if (!array[position]) {
        array[position] = [];
      }
      array[position].push(element);
    }
docs: Another slight optimization: sort the rules into bins according to the last element (observing quantifiers), so we can restrict the match against the stack to the subest of rules that match the top of the stack.  TODO(mesch): What we actually want is to compute states as in bison, so that we don't have to do any explicit and iterated match against the stack.