Some escape sequences that require parameters use delimiters. The
neutral apostrophe ' is a popular choice and shown in this
document. The neutral double quote " is also commonly seen.
Letters, numerals, and leaders can be used. Punctuation characters
are likely better choices, except for those defined as infix operators
in numeric expressions; see below.
\l'1.5i\[bu]' \" draw 1.5 inches of bullet glyphs
The following escape sequences don’t take arguments and thus are allowed
as delimiters:
\SP, \%, \|, \^, \{,
\}, \', \`, \-, \_, \!,
\?, \), \/, \,, \&, \:,
\~, \0, \a, \c, \d, \e,
\E, \p, \r, \t, and \u. However,
using them this way is discouraged; they can make the input confusing to
read.
A few escape sequences,
\A,
\b,
\o,
\w,
\X,
and \Z, accept a newline as a delimiter. Newlines that serve
as delimiters continue to be recognized as input line terminators.
A caf\o
e\(aa
in Paris
⇒ A café in Paris
Use of newlines as delimiters in escape sequences is also discouraged.
Finally, the escape sequences \D, \h, \H,
\l, \L, \N, \R, \s, \S,
\v, and \x prohibit many delimiters.
0-9 and the decimal point .
\%, \:, \{,
\}, \', \`, \-, \_, \!,
\/, \c, \e, and \p
Delimiter syntax is complex and flexible primarily for historical
reasons; the foregoing restrictions need be kept in mind mainly when
using groff in AT&T compatibility mode. GNU
troff keeps track of the nesting depth of escape sequence
interpolations, so the only characters you need to avoid using as
delimiters are those that appear in the arguments you input, not any
that result from interpolation. Typically, ' works fine.
See Implementation Differences.
$ groff -Tps
.de Mw
. nr wd \w'\\$1'
. tm "\\$1" is \\n(wd units wide.
..
.Mw Wet'suwet'en
.Mw Wet+200i
.cp 1 \" turn on compatibility mode
.Mw Wet'suwet'en
.Mw Wet'
.Mw Wet+200i
error→ "Wet'suwet'en" is 54740 units wide.
error→ "Wet'+200i" is 42610 units wide.
error→ "Wet'suwet'en" is 15860 units wide.
error→ "Wet'" is 15860 units wide.
error→ "Wet'+200i" is 14415860 units wide.
We see here that in compatibility mode, the part of the argument after
the ' delimiter escapes from its context and, if nefariously
crafted, influences the computation of the wd register’s value in
a surprising way.