The FAM string, a GNU extension, sets the font family for body
text; the default is ‘T’. The PS and VS registers
set the type size and vertical spacing (distance between text
baselines), respectively. The font family and type size are ignored on
terminal devices. Setting these parameters before the first call of a
heading, paragraphing, or (non-date) document description macro also
applies them to headers, footers, and (for FAM) footnotes.
Which font families are available depends on the output device; as a
convention, T selects a serif family (“Times”), H a
sans-serif family (“Helvetica”), and C a monospaced family
(“Courier”). The man page for the output driver documents its font
repertoire. Consult the groff(1) man page for lists of
available output devices and their drivers.
The hyphenation mode (as used by the hy request) is set from the
HY register. Setting HY to ‘0’ is equivalent to
using the nh request. This is a Tenth Edition Research Unix
extension.