So 63 random printable characters is the most that the specification allows a user to put in.

The first part must be a Type of up to 24 printable characters, including spaces.

The second part provides information about these keywords, and can be up to 100 printable characters long, including spaces.

This can be any string of printable characters and spaces up to 64 characters in length.

Up to 28 printable characters are allowed, including spaces.

If supplied, each entry may contain up to 100 printable characters, including spaces.

Is not a printable character or control code.

All you could send to them were the printable characters, plus a few simple commands like 'carriage return' and 'line feed'.

This is handy because some media (such as sheets of paper produced by typewriters) can transmit only printable characters.

Each line is a sequence of printable characters.