Use the CLASS command to indicate an "output class" or a "processing class" for the file being sent.
The CLASS statement must come after a FILE command and should preceed any DATA commands.

The syntax is
  CLASS     class code  

where
class code   is typically a single letter

The class code will almost certainly have local dependencies and/or restrictions.
This attribute is generally most useful for print jobs, though it can be used to specify other media types and may be applied to non-printed files.

An augmented syntax is
  CLASS     class code   [   devtype   ]  

where
class code   is typically a single letter
devtype   is a device type somehow related to the class