src/document/doc-builders.js/join
function join(sep, arr) {
  const res = [];

  for (let i = 0; i < arr.length; i++) {
    if (i !== 0) {
      res.push(sep);
    }

    res.push(arr[i]);
  }

  // eslint-disable-next-line prettier-internal-rules/no-doc-builder-concat
  return concat(res);
}