code: function pack(edit, count, removed, elements) {
      var children = new Array(count - 1);
      var g = 0;
      var bitmap = 0;
      for (var i = 0, len = elements.length; i < len; ++i) {
          if (i !== removed) {
              var elem = elements[i];
              if (elem && !isEmptyNode(elem)) {
                  children[g++] = elem;
                  bitmap |= 1 << i;
              }
          }
      }
      return IndexedNode(edit, bitmap, children);
  }
docs: Collapse an array node into a indexed node.
  
  @param edit Current edit.
  @param count Number of elements in new array.
  @param removed Index of removed element.
  @param elements Array node children before remove.