const formatter = (material: Document | string, url: URL) => {
  const title = (isString(material) ? material : material.title)
    .replace(/\s/g, " ") // スペースと改行を全て半角スペースにする
    .replaceAll("[", "［")
    .replaceAll("]", "］");
  return title ? `[${title} ${url}]` : `${url}`;
};