The troff installed on a 7th Edition Unix system writes code for a
GSI C/A/T machine.  Later, bwk modified troff to write a
/device-independent format/ (think TeX’s dvi), which can be
translated to the codes expected by different typesetting machines
using /post-processors/.  That device-independent format is still
in use today, by the different troff implementations.

Catdit is like a reverse C/A/T post-processor: It takes the code
for a C/A/T and converts it to the newer device-independent format.

SPDX-FileCopyrightText: Lennart Jablonka <humm@ljabl.com>
SPDX-License-Identifier: BlueOak-1.0.0