Normally grops should be invoked by using the groff command with a -Tps option. If no files are given, grops will read the standard input. A filename of - will also cause grops to read the standard input.
PostScript output is written to the standard output.
When grops is run by groff options can be passed to grops using the groff -P option. Normally grops produces output that conforms the Document Structuring Conventions version 3.0. Unfortunately some spoolers and previewers can't handle such output. The value of n controls what grops does to its output acceptable to such programs. A value of 0 will cause grops not to employ any workarounds.