Errnum

The right argument of 13!:8 is now limited
to be an integer between 1 and 255. For example:

   13!:8 ]9
|length error
|       13!:8]9
   'my own message' 13!:8 ]9
|my own message
|   'my own message'    13!:8]9
   'my own message' 13!:8 ]999
|limit error
|   'my own message'    13!:8]999