code: func isLikelyAlreadyCompressed(f fs.File) bool {
  	// TODO(vadimsh): We can sniff MIME type based on the content, e.g via
  	// https://bitbucket.org/taruti/mimemagic/src or http.DetectContentType. Not
  	// sure it's worth it.
  	return compressedExt.Has(strings.ToLower(path.Ext(f.Name())))
  }
docs: ////////////////////////////////////////////////////////////////////////////////
  // isLikelyAlreadyCompressed returns true for file format that use compression.
  //
  // It decides based only on the file name extension. For files that have an
  // optional compression, we assume it is enabled.