sub encode_title {
  my($title) = @_;

  $title =~ s/([^A-Za-z0-9])/sprintf '_%02X', ord $1/ge;

  return $title;
}

sub decode_title {
  my($title) = @_;

  if ($title =~ /[^A-Za-z0-9_]/ or
      $title =~ /_(?![A-F0-9]{2})/) {
    return undef;
  }

  $title =~ s/_(..)/chr hex $1/ge;

  return $title;
}