static _walk(builder, node) {
      if (typeof node === "string") {
        builder.addText(node);
      } else if (node.children) {
        builder.openNode(node);
        node.children.forEach((child) => this._walk(builder, child));
        builder.closeNode(node);
      }
      return builder;
    }
@param {Renderer} builder
@param {Node} node