code: func Untar(tarArchive io.Reader, dest string, options *TarOptions) error {
  	return untarHandler(tarArchive, dest, options, true)
  }
docs: // Untar reads a stream of bytes from `archive`, parses it as a tar archive,
  // and unpacks it into the directory at `dest`.
  // The archive may be compressed with one of the following algorithms:
  //  identity (uncompressed), gzip, bzip2, xz.
  // FIXME: specify behavior when target path exists vs. doesn't exist.