docs: def url_split(s3_url):
      """Split S3 URL and return a tuple of (bucket, key).
  
      S3 URL is expected to be of "s3://<bucket>/<key>" format.
      """
  
      assert isinstance(s3_url, str)
  
      match = re_s3_url.match(s3_url)
      if not match:
          raise UrlParseError('Error parsing S3 URL: "%s"' % s3_url)
  
      parts = match.groupdict()
      return (parts['bucket'], parts['key'])