docs: function (depth) {
          var height = 0;
          this.depth = depth;
          for (var i = 0; i < this.children.length; i++) {
              var child = this.children[i];
              child.updateDepthAndHeight(depth + 1);
              if (child.height > height) {
                  height = child.height;
              }
          }
          this.height = height + 1;
      }