In-RIP separations are spot colors that have been defined in an external RIP or in a graphics program and saved as a single job.
PostScript files with in-RIP separations normally require a special PostScript command to interpret the in-RIP information correctly. PostScript Level 3 printers support in-RIP separations, but PostScript level 2 printers do not.
By default, jobs with in-RIP separations are output as follows:
PostScript jobs created for a PostScript level 3 printer are output separated if the printer support in-RIP separation. If the printer does not support in-RIP separation, the job is output composite.
PostScript jobs created for a PostScript level 2 printer are always output composite, because spot color separations cannot be correctly interpreted.
Forcing in-RIP separation makes sure that the in-RIP information from the graphics program is processed, even if the special PostScript command is missing, and regardless of the type of PostScript printer that created the file.