by Trent A. Fisher and Werner Lemberg - The GNU Operating System

28 The GNU Troff Manual
.DT
[Macro]
Set tabs every 0.5 inches. Since this macro is always executed during a
call to the TH macro, it makes sense to call it only if the tab positions
have been changed.
.PD [nnn]
[Macro]
Adjust the empty space before a new paragraph (or section). The optional
argument gives the amount of space (default unit is ‘v’); without
parameter, the value is reset to its default value (1 line in nroff mode,
0.4 v otherwise).
This affects the macros SH, SS, TP, LP (as well as PP and P), IP, and HP.
The following two macros are included for BSD compatibility.
.AT [system [release]]
[Macro]
Alter the footer for use with AT&T manpages. This command exists only
for compatibility; don’t use it. The first argument system can be:
3 7th Edition (the default)
4 System III
5 System V
An optional second argument release to AT specifies the release number
(such as “System V Release 3”).
.UC [version]
[Macro]
Alters the footer for use with BSD manpages. This command exists only
for compatibility; don’t use it. The argument can be:
3 3rd Berkeley Distribution (the default)
4 4th Berkeley Distribution
5 4.2 Berkeley Distribution
6 4.3 Berkeley Distribution
7 4.4 Berkeley Distribution
4.1.5 Predefined strings
The following strings are defined:
\*[S]
Switch back to the default font size.
\*[HF]
The typeface used for headings. The default is ‘B’.
\*[R]
The ‘registered’ sign.
[String]
[String]
[String]