The description wasn't clear. I've changed the sentence:
Argument 4 is a string of up to 60 valid (upper case alphabetic or space) characters delimited by the `|'.
Argument 4 is a string of up to 60 valid characters (upper case letters or space if font is C5, or any printable character if font is C1) delimited by the `|'.
Thanks to Reid Barton for the report.