z/OS JES3 Initialization and Tuning Reference
SA32-1005-00
CLASS=
Specifies the message destination to which you want JES3 to
send network messages. This destination can be specified as a single
JES3 destination class or a single MCS routing code. Specify this
message destination on the consoles that you want to receive the network
messages.
If a routing code is used, nnn specifies a decimal number
from 1 through 28, or 41 through 128. IBM® reserves
routing codes 29 through 40 for it's use and will ignore these codes
if specified.