The intermediate output language of AT&T
first documented in the UNIX troff manual, with later
additions documented in A Typesetter-indenpendent TROFF, written
by Brian Kernighan.
gtroff intermediate output format is compatible with this
specification except for the following features.
groffdevices are also fundamentally different from the ones in AT&T
troff. For example, the AT&T PostScript device is called
postand has a resolution of only 720 units per inch, suitable for printers 20 years ago, while
psdevice has a resolution of 72000 units per inch. Maybe, by implementing some rescaling mechanism similar to the classical quasi device independence,
groffcould emulate AT&T's
gtroff, while AT&T
troffhas point (‘p’). This isn't an incompatibility but a compatible extension, for both units coincide for all devices without a
sizescaleparameter in the DESC file, including all postprocessors from AT&T and
groff's text devices. The few
groffdevices with a
sizescaleparameter either do not exist for AT&T
troff, have a different name, or seem to have a different resolution. So conflicts are very unlikely.
gtroffused this feature it is kept for compatibility reasons.