различия между GNU roff и AT&T troff (differences between GNU roff and AT&T troff)
Язык (Language)
groff features identifiers of arbitrary length, supports non-
integral point sizes, adds new escapes and requests, provides new
conditional tests, recognizes additional scaling indicators and
numerical operators, and extends the function of some escapes and
requests already present in AT&T troff.
Long names
groff introduces many new requests; with three exceptions, they
all have names longer than two characters. The names of number
registers, fonts, strings/macros/diversions, environments,
special characters (glyphs), and colors can be of any length.
More generally, anywhere AT&T troff supports an escape form that
uses an opening parenthesis '(' to introduce a two-character
argument, groff supports a square-bracketed form '[]' where the
argument within can be of arbitrary length.
Fractional point sizes and new scaling indicators
A scaled point is equal to 1/sizescale points, where sizescale is
a parameter specified in the device description file, DESC, and
defaults to 1. A new scale indicator 'z' has the effect of
multiplying by sizescale. Requests and escapes in groff
interpret arguments that represent a point size as being in units
of scaled points; that is, they evaluate such arguments using an
implied default scaling indicator of 'z'. Arguments treated in
this way comprise those to the escapes \H and \s, to the request
.ps, the third argument to the .cs request, and the second and
fourth arguments to the .tkf request.
For example, if sizescale is 1000, then a scaled point is one
one-thousandth of a point. The request '.ps 10.25' is synonymous
with '.ps 10.25z' and sets the point size to 10250 scaled points,
or 10.25 points.
Consequently, in groff, the number register \n[.s] can contain a
non-integral point size. The new number register \n[.ps] returns
the point size in scaled points.
It makes no sense to use the 'z' scale indicator in a numeric
expression whose default scaling indicator is neither 'u'
nor 'z', so groff disallows this. Similarly, it is nonsensical
to use a scaling indicator other than 'z' or 'u' in a numeric
expression whose default scaling indicator is 'z', so groff
disallows this as well.
Another new scaling indicator, 's', multiplies by the number of
basic units in a scaled point. For instance, '\n[.ps]s' is equal
to '1m' by definition. Do not confuse the 's' and 'z' scaling
indicators.
A further two new measurement units available in groff are 'M',
which indicates hundredths of an em, and 'f', which is defined as
65536 basic units. The latter provides convenient fractions for
color definitions with the .defcolor request. For example, 0.5f
equals 32768u.
Numeric expressions
Spaces are permitted in a numeric expression within parentheses.
Three new operators are available as well.
e1>?e2 Compute the maximum of e1 and e2.
e1<?e2 Compute the minimum of e1 and e2.
(c;e) Evaluate e using c as the default scaling indicator. If c
is missing, ignore scaling indicators in the evaluation
of e.
Conditional expressions
More conditions can be tested with the .if and .ie requests, as
well as the new .while request.
c g True if a glyph g is available, where g is a Unicode basic
Latin character; a groff special character \(xx or \[xxx];
\N'xxx'; or has been defined by any of the .char, .fchar,
.fschar, or .schar requests.
d name True if there is a string, macro, diversion, or request
called name.
F font True if a font called font exists. font is handled as if
it were opened with the .ft request (that is, font
translation and styles are applied), without actually
mounting it. This test doesn't load the complete font,
but only its header, to verify its validity.
m color
True if there is a color called color.
r reg True if there is a number register called reg.
S style
True if a style called style has been registered. Font
translation is applied.
v Always false. This condition is for compatibility with
certain other troff implementations only. (This refers to
vtroff, a translator that would convert the C/A/T output
from early-vintage AT&T troff to a form suitable for
Versatec and Benson-Varian plotters.)
Escape sequences
groff introduces several new escape sequences and extends the
syntax of a few AT&T troff escapes (namely, \D, \f, \k, \n, \$,
and \*). In the following list, escapes are collated
alphabetically at first, and then by symbol roughly in Unicode
code point order.
\A'anything'
This expands to 1 or 0, depending on whether anything is
or is not acceptable as the name of a string, macro,
diversion, number register, environment, font, or color.
It returns 0 if anything is empty. This is useful if you
want to look up user input in some sort of associative
table.
\B'anything'
This expands to 1 or 0, depending on whether anything is
or is not a valid numeric expression. It returns 0 if
anything is empty.
\D'...'
All drawing commands supported by the AT&T troff device-
independent intermediate output format are accepted. See
subsection 'Drawing Commands' below for GNU extensions.
\E This is equivalent to an escape character, but it is not
interpreted in copy mode. Strings to start and end
superscripting could be defined as follows.
.ds { \v'-.3m'\s'\En[.s]*6u/10u'
.ds } \s0\v'.3m'
The use of \E ensures that these definitions work even if
\*{ gets interpreted in copy mode (for example, by being
used in a macro argument).
\f[xxx]
Set font xxx. Additionally, \f[] is a new syntax form
equal to \fP, i.e., to return to the previous font.
\Ff
\F(fm
\F[fam]
Change font family. See the .fam request below. \F[]
switches to the previous font family, or to the default
family if there is none. \FP won't do this; it selects
font family 'P' instead.
\k(rg
\k[reg]
Mark horizontal position in register with two-character
name rg or arbitrarily long name reg.
\mx
\m(xx
\m[xxx]
Set drawing color. \m[] switches back to the previous
color.
\Mx
\M(xx
\M[xxx]
Set background color for filled objects drawn with the
\D'...' commands. \M[] switches back to the previous
color.
\n[xxx]
Interpolate number register xxx.
\On
\O[n] Suppress troff output. The escapes \O2, \O3, \O4, and \O5
are intended for internal use by grohtml.
\O0 Disable glyphs from being emitted to the device
driver, provided that the escape occurs at the
outer level (see \O3 and \O4).
\O1 Enable output of glyphs, provided that the escape
occurs at the outer level.
\O0 and \O1 also reset the registers \n[opminx],
\n[opminy], \n[opmaxx], and \n[opmaxy] to -1.
These four registers mark the top left and bottom
right hand corners of a box which encompasses all
written glyphs.
\O2 Provided that the escape occurs at the outer level,
enable output of glyphs and also write out to
stderr the page number and four registers
encompassing the glyphs previously written since
the last call to \O.
\O3 Begin a nesting level. At start-up, troff is at
outer level. This is really an internal mechanism
for grohtml while producing images. They are
generated by running the troff source through troff
to the PostScript device and ghostscript to produce
images in PNG format. The \O3 escape starts a new
page if the device is not html (to reduce the
possibility of images crossing a page boundary).
\O4 End a nesting level.
\O5[Pfilename]
This escape is grohtml specific. Provided that
this escape occurs at the outer nesting level,
write filename to stderr. The position of the
image, P, must be specified and must be one of l,
r, c, or i (left, right, centered, inline).
filename is associated with the production of the
next inline image.
\R'name ±n'
This has the same effect as
.nr name ±n
\s[±n]
\s±[n]
\s'±n'
\s±'n' Set the point size to n scaled points; n is a numeric
expression with a default scaling indicator of 'z'.
\Vx
\V(xx
\V[xxx]
Interpolate the contents of the environment variable xxx,
as returned by getenv(3). \V is interpreted in copy mode.
\Yx
\Y(xx
\Y[xxx]
This is approximately equivalent to \X'\*[xxx]'. However
the contents of the string or macro xxx are not
interpreted; also it is permitted for xxx to have been
defined as a macro and thus contain newlines (it is not
permitted for the argument to \X to contain newlines).
The inclusion of newlines requires an extension to the
AT&T troff output format, and confuses drivers that do not
know about this extension.
\Z'anything'
Print anything and then restore the horizontal and
vertical position; anything may not contain tabs or
leaders.
\# Everything up to and including the next newline is
ignored. This escape is interpreted even in copy mode.
\# is like \", except that \" does not ignore a newline;
the latter therefore cannot be used by itself for a whole-
line comment—it leaves a blank line on the input stream.
\$0 The name by which the current macro was invoked. The als
request can make a macro have more than one name.
\$(nn
\$[nnn]
In a macro or string, this gives the nn-th or nnn-th
argument. Macros and strings can have an unlimited number
of arguments.
\$* In a macro or string, the concatenation of all the
arguments separated by spaces.
\$@ In a macro or string, the concatenation of all the
arguments with each surrounded by double quotes, and
separated by spaces.
\$^ In a macro, the representation of all parameters as if
they were an argument to the ds request.
\) Like \& except that it behaves like a character declared
with the .cflags request to be transparent for the
purposes of end-of-sentence recognition.
\*[xxx arg1 arg2 ...]
Interpolate string xxx, taking arg1, arg2, ... as
arguments.
\/ Apply an italic correction: increase the width of the
preceding glyph so that the spacing between that glyph and
the following glyph is correct if the following glyph is a
roman glyph. For example, if an italic 'f' is immediately
followed by a roman right parenthesis, then in many fonts
the top right portion of the 'f' overlaps the top left of
the right parenthesis, which is ugly. Inserting \/
between them avoids this problem. Use this escape
sequence whenever an italic glyph is immediately followed
by a roman glyph without any intervening space.
\, Apply a left italic correction: modify the spacing of the
following glyph so that the spacing between that glyph and
the preceding glyph is correct if the preceding glyph is a
roman glyph. For example, if a roman left parenthesis is
immediately followed by an italic 'f', then in many fonts
the bottom left portion of the 'f' overlaps the bottom of
the left parenthesis, which is ugly. Inserting \, between
them avoids this problem. Use this escape sequence
whenever a roman glyph is immediately followed by an
italic glyph without any intervening space.
\: Insert a non-printing break point. That is, the word can
break there, but the soft hyphen glyph is not written to
the output if it does (in contrast to '\%'). This escape
is an input word boundary, so the remainder of the word is
subject to hyphenation as normal.
\?anything\?
When used in a diversion, this transparently embeds
anything in the diversion. anything is read in copy mode.
When the diversion is reread, anything is interpreted.
anything may not contain newlines; use \! if you want to
embed newlines in a diversion. The escape sequence \? is
also recognized in copy mode and turned into a single
internal code; it is this code that terminates anything.
Thus
.nr x 1
.nf
.di d
\?\\?\\\\?\\\\\\\\nx\\\\?\\?\?
.di
.nr x 2
.di e
.d
.di
.nr x 3
.di f
.e
.di
.nr x 4
.f
prints 4.
\[xxx] Print the special character (glyph) called xxx.
\[comp1 comp2 ...]
Print composite glyph consisting of multiple components.
Example: '\[A ho]' is capital letter A with ogonek which
finally maps to glyph name 'u0041_0328'. See Groff: The
GNU Implementation of troff, the groff Texinfo manual, for
details of how a glyph name for a composite glyph is
constructed, and groff_char(7) for a list of glyph name
components used in composite glyph names.
\~ This produces an unbreakable space that stretches like a
normal inter-word space when a line is adjusted.
Restricted requests
To mitigate risks from untrusted input documents, the pi and sy
requests are disabled by default. troff(1)'s -U option enables
the formatter's 'unsafe mode', restoring their function (and
enabling additional groff extension requests, open, opena, and
pso).
New requests
.aln new old
Create an alias new for an existing number register named
old, causing the names to refer to the same stored object.
If old is undefined, a warning of type 'reg' is generated
and the request is ignored. To remove a number register
alias, call .rr on its name. A number register's contents
do not become inaccessible until it has no more names.
.als new old
Create an alias new for the existing request, string,
macro, or diversion named old, causing the names to refer
to the same stored object. If old is undefined, a warning
of type 'mac' is generated and the request is ignored.
The .am, .as, .da, .de, .di, and .ds requests (together
with their variants) only create a new object if the name
of the macro, diversion, or string is currently undefined
or if it is defined as a request; normally, they modify
the value of an existing object. To remove an alias,
simply call .rm on its name. The object itself is not
destroyed until it has no more names.
.am1 xx yy
Similar to .am, but compatibility mode is switched off
during execution. To be more precise, a 'compatibility
save' token is inserted at the beginning, and a
'compatibility restore' token at the end. As a
consequence, the requests .am, .am1, .de, and .de1 can be
intermixed freely since the compatibility save/restore
tokens only affect the macro parts defined by .am1 and
.ds1.
.ami xx yy
Append to macro indirectly. See the dei request below.
.ami1 xx yy
Same as the ami request but compatibility mode is switched
off during execution.
.as1 name string
Similar to .as, but compatibility mode is switched off
when the appended portion of the string is later
interpolated. To be more precise, a 'compatibility save'
token is inserted at the beginning of the appended string
string, and a 'compatibility restore' token at the end.
As a consequence, the requests .as, .as1, .ds, and .ds1
can be intermixed freely since the compatibility save/
restore tokens only affect the (sub)strings defined by
.as1 and .ds1.
.asciify div
Unformat the diversion div in a way such that Unicode
basic Latin (ASCII) characters, characters translated with
the .trin request, space characters, and some escape
sequences, that were formatted and diverted into div are
treated like ordinary input characters when div is reread.
Doing so can be useful in conjunction with the .writem
request. .asciify can be also used for gross hacks; for
example, the following sets register n to 1.
.tr @.
.di x
@nr n 1
.br
.di
.tr @@
.asciify x
.x
.asciify cannot return all items in a diversion to their
source equivalent: nodes such as those produced by \N[...]
will remain nodes, so the result cannot be guaranteed to
be a pure string. See section 'Copy mode' in groff(7).
Glyph parameters such as the type face and size are not
preserved; use .unformat to achieve that.
.backtrace
Write a backtrace of the input stack to the standard error
stream. Also see the -b option of troff(1).
.blm [name]
Set a blank line macro (trap). If a blank line macro is
thus defined, groff executes macro when a blank line is
encountered in the input file, instead of the usual
behavior. A line consisting only of spaces is also
treated as blank and subject to this trap. If no argument
is supplied, the default blank line behavior is
(re-)established.
.box name
.boxa name
These requests are similar to the di and da requests,
respectively, with the exception that any pending output
line does not become part of the diversion (i.e., a box
diversion always starts on a new output line) but is
restored after ending the diversion, discarding any
partially collected line in the diversion.
.break Break out of a while loop. See also the while and
continue requests. Be sure not to confuse this with the
br request.
.brp This is the same as \p.
.cflags n c1 c2 ...
Assign properties encoded by the number n to characters
c1, c2, and so on.
Input characters, including special characters introduced
by an escape, have certain properties associated with
them. (Note that output glyphs don't have such
properties. In groff, a glyph is a numbered box with a
given height above and depth below the baseline, and a
width—nothing more.) These properties can be modified
with this request. The first argument is the sum of the
desired flags and the remaining arguments are the
characters to be assigned those properties. Spaces
between the cn arguments are optional. Any argument cn
can be a character class defined with the .class request
rather than an individual character.
The non-negative integer n is the sum of any of the
following. Some combinations are nonsensical, such as
'33' (1 + 32).
1 Recognize the character as ending a sentence if
followed by a newline or two spaces. Initially,
characters '.?!' have this property.
2 Enable breaks before the character. A line is not
broken at a character with this property unless the
characters on each side both have non-zero
hyphenation codes. This exception can be
overridden by adding 64. Initially, no characters
have this property.
4 Enable breaks after the character. A line is not
broken at a character with this property unless the
characters on each side both have non-zero
hyphenation codes. This exception can be
overridden by adding 64. Initially, characters
'-\[hy]\[em]' have this property.
8 Mark the glyph associated with this character as
overlapping other instances of itself horizontally.
Initially, characters
'\[ul]\[rn]\[ru]\[radicalex]\[sqrtex]' have this
property.
16 Mark the glyph associated with this character as
overlapping other instances of itself vertically.
Initially, the character '\[br]' has this property.
32 Mark the character as transparent for the purpose
of end-of-sentence recognition. In other words, an
end-of-sentence character followed by any number of
characters with this property is treated as the end
of a sentence if followed by a newline or two
spaces. This is the same as having a zero space
factor in TeX. Initially, characters
''")]*\[dg]\[dd]\[rq]\[cq]' have this property.
64 Ignore hyphenation codes of the surrounding
characters. Use this value in combination with
values 2 and 4. Initially, no characters have this
property.
For example, if you need an automatic break point
after the en-dash in numerical ranges like
'3000–5000', insert
.cflags 68 \[en]
into your document. Note, however, that this can
lead to bad layout if done without thinking; in
most situations, a better solution than changing
the .cflags value is inserting '\:' right after the
hyphen at the places that really need a break
point.
The remaining values were implemented for East Asian
language support; those who use alphabetic scripts
exclusively can disregard them.
128 Prohibit a break before the character, but allow a
break after the character. This works only in
combination with values 256 and 512 and has no
effect otherwise. Initially, no characters have
this property.
256 Prohibit a break after the character, but allow a
break before the character. This works only in
combination with values 128 and 512 and has no
effect otherwise. Initially, no characters have
this property.
512 Allow a break before or after the character. This
works only in combination with values 128 and 256
and has no effect otherwise. Initially, no
characters have this property.
In contrast to values 2 and 4, the values 128, 256, and
512 work pairwise. If, for example, the left character
has value 512, and the right character 128, no break will
be automatically inserted between them. If we use value 6
instead for the left character, a break after the
character can't be suppressed since the neighboring
character on the right doesn't get examined.
.char g string
Define a new character or glyph g to be string, which can
be empty. More precisely, .char defines a groff object
(or redefines an existing one) that is accessed with the
name g on input, and produces string on output. Every
time glyph g needs to be printed, string is processed in a
temporary environment and the result is wrapped up into a
single object. Compatibility mode is turned off and the
escape character is set to \ while string is processed.
Any emboldening, constant spacing, or track kerning is
applied to this object rather than to individual glyphs in
string.
An object defined by this request can be used just like a
normal glyph provided by the output device. In
particular, other characters can be translated to it with
the .tr request; it can be made the leader glyph with the
.lc request; repeated patterns can be drawn with it using
the \l and \L escape sequences; and words containing g can
be hyphenated correctly, if the .hcode request is used to
give the object a hyphenation code.
There is a special anti-recursion feature: use of the
object within its own definition is handled like a normal
character (one not defined with .char).
The .tr and .trin requests take precedence if .char
accesses the same symbol.
A glyph definition can be removed with the .rchar request.
.chop object
Remove the last character from the macro, string, or
diversion named object. This is useful for removing the
newline from the end of a diversion that is to be
interpolated as a string. This request can be used
repeatedly on the same object; see section 'Gtroff
Internals' in Groff: The GNU Implementation of troff, the
groff Texinfo manual, for details on nodes inserted
additionally by groff.
.class name c1 c2 ...
Define a character class (or simply 'class') name
comprising the characters or range expressions c1, c2, and
so on.
A class thus defined can then be referred to in lieu of
listing all the characters within it. Currently, only the
.cflags request can handle references to character
classes.
In the request's simplest form, each cn is a character (or
special character).
.class [quotes] ' \[aq] \[dq] \[oq] \[cq] \[lq] \[rq]
Since class and glyph names share the same name space, it
is recommended to start and end the class name with '['
and ']', respectively, to avoid collisions with existing
character names defined by groff or the user (with .char
and related requests). This practice applies the presence
of ']' in the class name to prevent the usage of the
special character escape form '\[...]', thus you must use
the \C escape to access a class with such a name.
You can also use a character range expression consisting
of a start character followed by '-' and then an end
character. Internally, groff converts these two character
names to Unicode code points (according to the groff glyph
list [GGL]), which determine the start and end values of
the range. If that fails, the class definition is
skipped. Furthermore, classes can be nested.
.class [prepunct] , : ; > }
.class [prepunctx] \C'[prepunct]' \[u2013]-\[u2016]
The class '[prepunctx]' thus contains the contents of the
class '[prepunct]' and characters in the range
U+2013–U+2016.
If you want to include '-' in a class, it must be the
first character value in the argument list, otherwise it
gets misinterpreted as part of the range syntax.
Note that it is not possible to use class names as end
points of range definitions.
A typical use of the .class request is to control line-
breaking and hyphenation rules as defined by the .cflags
request. For example, to inhibit line breaks before the
characters belonging to the '[prepunctx]' class defined in
the previous example, you can write the following.
.cflags 2 \C'[prepunctx]'
.close stream
Close the stream named stream; stream will no longer be an
acceptable argument to the write request. See the open
request.
.composite glyph1 glyph2
Map glyph name glyph1 to glyph name glyph2 if it is used
in \[...] with more than one component.
.continue
Finish the current iteration of a while loop. See also
the while and break requests.
.color n
If n is non-zero or missing, enable colors (this is the
default), otherwise disable them.
.cp n If n is non-zero or missing, enable compatibility mode,
otherwise disable it. In compatibility mode, long names
are not recognized, and the incompatibilities caused by
long names do not arise.
.defcolor xxx scheme color_components
Define color xxx. scheme can be one of the following
values: rgb (three components), cmy (three components),
cmyk (four components), and gray or grey (one component).
Color components can be given either as a hexadecimal
string or as positive decimal integers in the range
0–65535. A hexadecimal string contains all color
components concatenated; it must start with either # or
##. The former specifies hex values in the range 0–255
(which are internally multiplied by 257), the latter in
the range 0–65535. Examples: #FFC0CB (pink),
##ffff0000ffff (magenta). A new scaling indicator,
'f' has has been introduced which multiplies its value
by 65536; this makes it convenient to specify color
components as fractions in the range 0 to 1. Example:
.defcolor darkgreen rgb 0.1f 0.5f 0.2f
Note that f is the default scaling indicator for the
defcolor request, thus the above statement is equivalent
to
.defcolor darkgreen rgb 0.1 0.5 0.2
The color named default (which is device-specific) can't
be redefined. It is possible that the default color for
\M and \m is not the same.
.de1 xx yy
Similar to .de, but compatibility mode is switched off
during execution. On entry, the current compatibility
mode is saved and restored at exit.
.dei xx [yy]
Define macro indirectly, with the name of the macro to be
defined in string xx and the name of the end macro
terminating its definition in string yy.
.dei1 xx [yy]
As .dei, but compatibility mode is switched off when the
definition of the macro named in the string xx is
executed.
.device anything
This is (almost) the same as the \X escape. anything is
read in copy mode; a leading " is stripped.
.devicem xx
This is the same as the \Y escape (to embed the contents
of a macro into the intermediate output preceded with
'x X').
.do name ...
Interpret the string, request, diversion, or macro name
(along with any arguments) with compatibility mode
disabled. Note that compatibility mode is restored (only
if it was active) when the expansion of name is
interpreted; that is, the restored compatibility state
applies to the contents of the macro, string, or diversion
name as well as data read from files or pipes if name is
any of the so, soquiet, mso, msoquiet, or pso requests.
For example,
.de mac1
FOO
..
.de1 mac2
groff
.mac1
..
.de mac3
compatibility
.mac1
..
.de ma
\\$1
..
.cp 1
.do mac1
.do mac2 \" mac2, defined with .de1, calls "mac1"
.do mac3 \" mac3 calls "ma" with argument "c1"
.do mac3 \[ti] \" groff syntax accepted in .do arguments
results in
FOO groff FOO compatibility c1 ~
as output.
.ds1 name string
Similar to .ds, but compatibility mode is switched off
when the string is later interpolated. To be more
precise, a 'compatibility save' token is inserted at the
beginning of the string, and a 'compatibility restore'
token at the end.
.ecr Restore the escape character saved with ecs, or set escape
character to '\' if none has been saved.
.ecs Save the current escape character.
.evc environment
Copy the contents of environment to the current
environment.
The following environment data are not copied:
• a partially collected line, if present;
• the interruption status of the previous input line
(due to use of the \c escape sequence);
• the count of remaining lines to center, to right-
justify, or to underline (with or without
underlined spaces; all set to zero);
• the activation status of temporary indentation;
• input traps and their associated data;
• the activation status of line numbering (which can
be reactivated with '.nm +0'); and
• the count of consecutive hyphenated lines (set to
zero).
.fam [family]
Set the font family to family. If no argument is given,
switch to the previous font family, or the default family
if there is none. Use '\F[]' to do this with an escape
sequence; '\FP' selects font family 'P' instead. The
initial font family is 'T' (Times), but can be overridden
by the output device—see groff_font(5)). The current font
family is associated with the environment.
.fchar c string
Define fallback character (or glyph) c to be string. The
syntax of this request is the same as the char request;
the only difference is that a glyph defined with char
hides the glyph with the same name in the current font,
whereas a glyph defined with .fchar is checked only if the
particular glyph isn't found in the current font. This
test happens before checking special fonts.
.fcolor c
Set the fill color to c. If c is missing, switch to the
previous fill color.
.fschar f c string
Define fallback character (or glyph) c for font f to be
string. The syntax of this request is the same as the
char request (with an additional argument to specify the
font); a glyph defined with fschar is searched after the
list of fonts declared with the fspecial request but
before the list of fonts declared with .special.
.fspecial f s1 s2 ...
When the current font is f, fonts s1, s2, ... are special,
that is, they are searched for glyphs not in the current
font. Any fonts specified in the .special request are
searched after fonts specified in the .fspecial request.
Without argument, reset the list of global special fonts
to be empty.
.ftr f g
Translate font f to g. Whenever a font named f is
referred to in an \f escape sequence, in the F and S
conditional operators, or in the ft, ul, bd, cs, tkf,
special, fspecial, fp, or sty requests, font g is used.
If g is missing, or equal to f then font f is not
translated.
.fzoom f zoom
Set zoom factor zoom for font f. zoom must a non-negative
integer multiple of 1/1000th. If it is missing or is
equal to zero, it means the same as 1000, namely no
magnification. f must be a real font name, not a style.
.gcolor c
Set the glyph color to c. If c is missing, switch to the
previous glyph color.
.hcode c1 code1 [c2 code2] ...
Set the hyphenation code of character c1 to code1, that of
c2 to code2, and so on. A hyphenation code must be a
single input character (not a special character) other
than a digit or a space. The request is ignored if it has
no parameters.
For hyphenation to work, hyphenation codes must be set up.
At start-up, groff assigns hyphenation codes to the
letters 'a–z' (mapped to themselves), to the letters 'A–Z'
(mapped to 'a–z'), and zero to all other characters.
Normally, hyphenation patterns contain only lowercase
letters which should be applied regardless of case. In
other words, they assume that the words 'FOO' and 'Foo'
should be hyphenated exactly as 'foo' is. The .hcode
request extends this principle to letters outside the
Unicode basic Latin alphabet; without it, words containing
such letters won't be hyphenated properly even if the
corresponding hyphenation patterns contain them.
.hla lang
Set the hyphenation language to lang. Hyphenation
exceptions specified with the .hw request and hyphenation
patterns and exceptions specified with the .hpf and .hpfa
requests are associated with the hyphenation language.
The .hla request is usually invoked by a localization
file, which is in turn loaded by the troffrc or
troffrc-end file; see the .hpf request below.
The hyphenation language is associated with the
environment.
.hlm [n]
Set the maximum number of consecutive hyphenated lines
to n. If n is negative, there is no maximum. If omitted,
n is -1. This value is associated with the environment.
Only lines output from a given environment count towards
the maximum associated with that environment. Hyphens
resulting from \% are counted; explicit hyphens are not.
.hpf pattern-file
Read hyphenation patterns from pattern-file. This file is
sought in the same way that macro files are with the .mso
request or the -mname command-line option to groff(1).
The pattern-file should have the same format as (simple)
TeX pattern files. More specifically, the following
scanning rules are implemented.
• A percent sign starts a comment (up to the end of
the line) even if preceded by a backslash.
• 'Digraphs' like \$ are not supported.
• '^^xx' (where each x is 0–9 or a–f) and ^^c
(character c in the code point range 0–127 decimal)
are recognized; other uses of ^ cause an error.
• No macro expansion is performed.
• hpf checks for the expression \patterns{...}
(possibly with whitespace before or after the
braces). Everything between the braces is taken as
hyphenation patterns. Consequently, '{' and '}'
are not allowed in patterns.
• Similarly, \hyphenation{...} gives a list of
hyphenation exceptions.
• \endinput is recognized also.
• For backwards compatibility, if \patterns is
missing, the whole file is treated as a list of
hyphenation patterns (except that the '%' character
is recognized as the start of a comment).
Use the .hpfcode request (see below) to map the encoding
used in hyphenation pattern files to groff's input
encoding.
The set of hyphenation patterns is associated with the
hyphenation language set by the .hla request. The .hpf
request is usually invoked by a localization file loaded
by the troffrc file. By default, troffrc loads the
localization file for English. (As of groff 1.23.0,
localization files for Czech (cs), German (de), English
(en), French (fr), Japanese (ja), Swedish (sv), and
Chinese (zh) exist.) For Western languages, the
localization file sets the hyphenation mode and loads
hyphenation patterns and exceptions.
A second call to .hpf (for the same language) replaces the
old patterns with the new ones.
Invoking .hpf causes an error if there is no hyphenation
language.
If no .hpf request is specified (either in the document,
in a file loaded at start-up, or in a macro package),
groff won't automatically hyphenate at all.
.hpfa pattern-file
As .hpf, except that the hyphenation patterns and
exceptions from pattern-file are appended to the patterns
already applied to the hyphenation language of the
environment.
.hpfcode a b [c d] ...
Define mapping values for character codes in pattern
files. This is an older mechanism no longer used by
groff's own macro files; for its successor, see .hcode
above. .hpf or .hpfa aplly the mapping after reading or
appending to the active list of patterns. Its arguments
are pairs of character codes—integers from 0 to 255. The
request maps character code a to code b, code c to code d,
and so on. Character codes that would otherwise be
invalid in groff can be used. By default, every code maps
to itself except those for letters 'A' to 'Z', which map
to those for 'a' to 'z'.
.hym [length]
Set the (right) hyphenation margin to length. If the
adjustment mode is not 'b' or 'n', the line is not
hyphenated if it is shorter than length. Without an
argument, the default hyphenation margin is reset to its
default value, 0. The default scaling indicator is 'm'.
The hyphenation margin is associated with the environment.
A negative argument resets the hyphenation margin to zero,
emitting a warning of type 'range'.
.hys [hyphenation-space]
Suppress hyphenation of the line in adjustment modes 'b'
or 'n', if it can be justified by adding no more than
hyphenation-space extra space to each inter-word space.
Without an argument, the hyphenation space adjustment
threshold is set to its default value, 0. The default
scaling indicator is 'm'. The hyphenation space
adjustment threshold is associated with the current
environment.
A negative argument resets the hyphenation space
adjustment threshold to zero, emitting a warning of type
'range'.
.itc n name
As .it, but text lines interrupted with the \c escape are
not applied to the line count.
.kern n
If n is non-zero or missing, enable pairwise kerning,
otherwise disable it.
.length reg anything
Compute the number of characters in anything and return
the count in the number register reg. If reg doesn't
exist, it is created. anything is read in copy mode.
.ds xxx abcd\h'3i'efgh
.length yyy \*[xxx]
\n[yyy]
14
.linetabs n
If n is non-zero or missing, enable line-tabs mode,
otherwise disable it (which is the default). In line-tabs
mode, tab distances are computed relative to the (current)
output line. Otherwise they are taken relative to the
input line. For example, the following
.ds x a\t\c
.ds y b\t\c
.ds z c
.ta 1i 3i
\*x
\*y
\*z
yields
a b c
In line-tabs mode, the same code gives
a b c
Line-tabs mode is associated with the current environment;
the read-only number register \n[.linetabs] is set to 1 if
in line-tabs mode, and 0 otherwise.
.lsm [name]
Set the leading space macro (trap) to name. If there are
leading space characters on an input line, name is invoked
in lieu of the usual roff behavior; the leading spaces are
removed. The count of leading spaces on an input line is
stored in \n[lsn], and the amount of corresponding
horizontal motion in \n[lss], irrespective of whether a
leading space trap is set. When it is, the leading spaces
are removed from the input line, and no motion is produced
before calling name. If no argument is supplied, the
default leading space behavior is (re-)established.
.mso file
The same as the so request except that file is searched
for in the same directories as macro files for the -m
command-line option. If the file name to be included has
the form name.tmac and it isn't found, .mso tries to
include tmac.name instead and vice versa. If file does
not exist, a warning of type 'file' is emitted and the
request has no other effect.
.msoquiet file
As .mso, but no warning is emitted if file does not exist.
.nop anything
Interpret anything as if it were an input line. This is
similar to '.if 1'. .nop is not really 'no operation';
its argument is processed—unconditionally. It can be used
to cause text lines to share indentation with surrounding
control lines.
.nroff Make the n built-in condition true and the t built-in
condition false. This can be reversed using the troff
request.
.open stream filename
Open filename for writing and associate the stream named
stream with it. See also the close and write requests.
.opena stream filename
Like open, but if filename exists, append to it instead of
truncating it.
.output string
Emit string directly to the intermediate output (subject
to copy-mode interpretation); this is similar to \! used
at the top level. An initial double quote in string is
stripped off to allow initial blanks.
.pev Report the state of the current environment followed by
that of all other environments to the standard error
stream.
.pnr Print the names and contents of all currently defined
number registers on stderr.
.psbb filename
Get the bounding box of a PostScript image filename. This
file must conform to Adobe's Document Structuring
Conventions; the command looks for a %%BoundingBox comment
to extract the bounding box values. After a successful
call, the coordinates (in PostScript units) of the lower
left and upper right corner can be found in the registers
\n[llx], \n[lly], \n[urx], and \n[ury], respectively. If
some error has occurred, the four registers are set to
zero.
.pso command
This behaves like the so request except that input comes
from the standard output of command.
.ptr Print the names and positions of all traps (not including
input line traps and diversion traps) on stderr. Empty
slots in the page trap list are printed as well, because
they can affect the priority of subsequently planted
traps.
.pvs ±n
Set the post-vertical line space to n; default scaling
indicator is 'p'. This value is added to each line after
it has been output. With no argument, the post-vertical
line space is set to its previous value.
The total vertical line spacing consists of four
components: .vs and \x with a negative value which are
applied before the line is output, and .pvs and \x with a
positive value which are applied after the line is output.
.rchar c1 c2 ...
Remove the definitions of glyphs c1, c2, and so on. This
undoes the effect of a .char request.
.return
Within a macro, return immediately. If called with an
argument, return twice, namely from the current macro and
from the macro one level higher. No effect otherwise.
.rfschar f c1 c2 ...
Remove the font-specific definitions of glyphs c1, c2, ...
for font f. Whitespace is optional between cn arguments.
See .fschar.
.rj
.rj n Right justify the next n input lines. Without an argument
right justify the next input line. The number of lines to
be right justified is available in the \n[.rj] register.
This implicitly does .ce 0. The ce request implicitly
does .rj 0.
.rnn xx yy
Rename number register xx to yy. If xx doesn't exist, the
request is ignored.
.schar c string
Define global fallback character (or glyph) c to be
string. The syntax of this request is the same as the
char request; a glyph defined with schar is searched after
the list of fonts declared with the special request but
before the mounted special fonts.
.shc glyph
Set the soft hyphen glyph, inserted when a word is
hyphenated automatically or at a hyphenation character,
to glyph. If the argument is omitted, the soft hyphen
glyph is set to the default, \[hy]. If the selected glyph
does not exist in the font in use at a potential
hyphenation point, then the line is not broken at that
point. Neither character definitions (specified with the
.char request) nor translations (specified with the .tr
request) are considered when assigning the soft hyphen
glyph.
.shift n
In a macro, shift the arguments by n positions: argument i
becomes argument i-n; arguments 1 to n are no longer
available. If n is missing, arguments are shifted by 1.
Shifting by negative amounts is currently undefined.
.sizes s1 s2 ... sn [0]
This request is similar to the sizes command of a DESC
file. It sets the available font sizes for the current
font to s1, s2, ... sn scaled points. The list of sizes
can be terminated by an optional '0'. Each si can also be
a range of sizes m–n. Contrary to the font file command,
the list can't extend over more than a single line.
.soquiet file
As .so, but no warning is emitted if file does not exist.
.special s1 s2 ...
Fonts s1, s2, ... are special and are searched for glyphs
not in the current font. Without arguments, reset the
list of special fonts to be empty.
.spreadwarn [limit]
Emit a break warning if the additional space inserted for
each space between words in an output line adjusted to
both margins with '.ad b' is larger than or equal to
limit. A negative value is treated as zero; an absent
argument toggles the warning on and off without changing
limit. The default scaling indicator is m. At startup,
.spreadwarn is inactive and limit is 3 m.
For example,
.spreadwarn 0.2m
causes a warning if break warnings are not suppressed and
troff must add 0.2 m or more for each interword space in a
line. See troff(1) for warning types and control.
.stringdown str
.stringup str
Alter the string named str by replacing each of its bytes
with its lowercase (down) or uppercase (up) version (if
one exists). groff special characters (see groff_char(7))
can be used and the output will usually transform in the
expected way due to the regular naming convention of the
special character escapes.
.ds resume R\['e]sum\['e]\"
\*[resume] \# Résumé
.stringdown resume
\*[resume] \# résumé
.stringup resume
\*[resume] \# RÉSUMÉ
.sty n f
Associate style f with font position n. A font position
can be associated either with a font or with a style. The
current font is the index of a font position and so is
also either a font or a style. When it is a style, the
font that is actually used is the font the name of which
is the concatenation of the name of the current family and
the name of the current style. For example, if the
current font is 1 and font position 1 is associated with
style R and the current font family is T, then font TR is
used. If the current font is not a style, then the
current family is ignored. When the requests cs, bd, tkf,
uf, or fspecial are applied to a style, then they are
applied instead to the member of the current family
corresponding to that style. The default family can be
set with the -f command-line option. The styles command
in the DESC file controls which font positions (if any)
are initially associated with styles rather than fonts.
.substring str start [end]
Replace the string named str with its substring bounded by
the indices start and end, inclusive. The first character
in the string has index 0. If end is omitted, it is
implicitly set to the largest valid value (the string
length minus one). Negative indices count backwards from
the end of the string: the last character has index -1,
the character before the last has index -2, and so on.
.ds xxx abcdefgh
.substring xxx 1 -4
\*[xxx]
bcde
.substring xxx 2
\*[xxx]
de
.tkf f s1 n1 s2 n2
Enable track kerning for font f. When the current font
is f the width of every glyph is increased by an amount
between n1 and n2; when the current point size is less
than or equal to s1 the width is increased by n1; when it
is greater than or equal to s2 the width is increased by
n2; when the point size is greater than or equal to s1 and
less than or equal to s2 the increase in width is a linear
function of the point size.
.tm1 string
Similar to the tm request, string is read in copy mode and
written on the standard error, but an initial double quote
in string is stripped off to allow initial blanks.
.tmc string
Similar to tm1 but without writing a final newline.
.trf filename
Transparently output the contents of file filename. Each
line is output as if preceded by \!; however, the lines
are not subject to copy-mode interpretation. If the file
does not end with a newline, then a newline is added. For
example, you can define a macro x containing the contents
of file f, using
.di x
.trf f
.di
Unlike with the cf request, the file cannot contain
characters, such as NUL, that are not valid troff input
characters.
.trin abcd
This is the same as the tr request except that the asciify
request uses the character code (if any) before the
character translation. Example:
.trin ax
.di xxx
a
.br
.di
.xxx
.trin aa
.asciify xxx
.xxx
The result is x a. Using tr, the result would be x x.
.trnt abcd
This is the same as the tr request except that the
translations do not apply to text that is transparently
throughput into a diversion with \!. For example,
.tr ab
.di x
\!.tm a
.di
.x
prints b; if trnt is used instead of tr it prints a.
.troff Make the n built-in condition false, and the t built-in
condition true. This undoes the effect of the nroff
request.
.unformat div
Like .asciify, unformat the diversion div. However,
.unformat handles only tabs and spaces between words, the
latter usually arising from spaces or newlines in the
input. Tabs are treated as input tokens, and spaces
become adjustable again. The vertical sizes of lines are
not preserved, but glyph information (font, type size,
space width, and so on) is retained.
.vpt n Enable vertical position traps if n is non-zero, disable
them otherwise. Vertical position traps are traps set by
the wh or dt requests. Traps set by the it request are
not vertical position traps. The parameter that controls
whether vertical position traps are enabled is global.
Initially, vertical position traps are enabled.
.warn n
Control warnings. n is the sum of the numbers associated
with each warning that is to be enabled; all other
warnings are disabled. The number associated with each
warning is listed in troff(1). For example, .warn 0
disables all warnings, and .warn 1 disables all warnings
except that about missing glyphs. If n is not given, all
warnings are enabled.
.warnscale si
Set the scaling indicator used in warnings to si. Valid
values for si are u, i, c, p, and P. At startup, it is
set to i.
.while cond-expr anything
Evaluate the conditional expression cond-expr, and
repeatedly execute anything unless and until cond-expr
evaluates false. See also the break and continue
requests.
The body of a while request is treated like the body of a
de request: troff temporarily stores it in a macro that is
deleted after the loop exits. It can considerably slow
down a macro if the body of the while request (within the
macro) is large. Each time the macro is executed, the
while body is parsed and stored again as a temporary
macro.
The traditional and often better solution (AT&T troff
lacked the while request) is to use a recursive macro
instead that is parsed only once during its definition.
The number of available recursion levels is set to 1000
(this is a compile-time constant value of troff).
The closing brace of a while body must end a line.
.write stream anything
Write anything to the stream named stream. stream must
previously have been the subject of an open request.
anything is read in copy mode; a leading " is stripped.
.writec stream anything
Similar to write but without writing a final newline.
.writem stream xx
Write the contents of the macro or string xx to the stream
named stream. stream must previously have been the
subject of an open request. xx is read in copy mode.
Extended requests
.cf filename
When used in a diversion, this embeds in the diversion an
object which, when reread, will cause the contents of
filename to be transparently copied through to the output.
In AT&T troff, the contents of filename are immediately
copied through to the output regardless of whether there
is a current diversion; this behavior is so anomalous that
it must be considered a bug.
.de xx yy
.am xx yy
.ds xx yy
.as xx yy
In compatibility mode, these requests behave similarly to
.de1, .am1, .ds1, and .as1, respectively: a 'compatibility
save' token is inserted at the beginning, and a
'compatibility restore' token at the end, with
compatibility mode switched on during execution.
.hy n New values 16 and 32 are available; the former enables
hyphenation before the last character in a word, and the
latter enables hyphenation after the first character in a
word.
.ss word-space-size additional-sentence-space-size
A second argument to the .ss request sets the amount of
additional space separating sentences on the same output
line. If omitted, this amount is set to word-space-size.
The arguments' units are twelfths of the space width of
the current font (see groff_font(5)) and default to 12.
.ta [[n1 n2 ... nn ]T r1 r2 ... rn]
groff supports an extended syntax to specify repeating tab
stops after the 'T' mark. These values are always taken
as relative distances from the previous tab stop. This is
the idiomatic way to specify tab stops at equal intervals
in groff.
The syntax summary above instructs groff to set tabs at
positions n1, n2, ..., nn, then at nn+r1, nn+r2, ...,
nn+rn, then at nn+rn+r1, nn+rn+r2, ..., nn+rn+rn, and so
on.
New number registers
The following read-only registers are available:
\n[.br]
Within a macro call, it is set to 1 if the macro is called
with the 'normal' control character ('.' by default), and
set to 0 otherwise. This allows the reliable modification
of requests.
.als bp*orig bp
.de bp
.tm before bp
.ie \\n[.br] .bp*orig
.el 'bp*orig
.tm after bp
..
Using this register outside of a macro makes no sense (it
always returns zero in such cases).
\n[.C] 1 if compatibility mode is in effect, 0 otherwise.
\n[.cdp]
The depth of the last glyph added to the current
environment. It is positive if the glyph extends below
the baseline.
\n[.ce]
The number of lines remaining to be centered, as set by
the ce request.
\n[.cht]
The height of the last glyph added to the current
environment. It is positive if the glyph extends above
the baseline.
\n[.color]
1 if colors are enabled, 0 otherwise.
\n[.cp]
Within a .do request, holds the saved value of
compatibility mode (see \n[.C] above).
\n[.csk]
The skew of the last glyph added to the current
environment. The skew of a glyph is how far to the right
of the center of a glyph the center of an accent over that
glyph should be placed.
\n[.ev]
The name or number of the current environment. This is a
string-valued register.
\n[.fam]
The current font family. This is a string-valued
register.
\n[.fn]
The current (internal) real font name. This is a string-
valued register. If the current font is a style, the
value of \n[.fn] is the proper concatenation of family and
style name.
\n[.fp]
The number of the next free font position.
\n[.g] Always 1. Macros should use this to determine whether
they are running under GNU troff.
\n[.height]
The current height of the font as set with \H.
\n[.hla]
The hyphenation language in the current environment.
\n[.hlc]
The count of immediately preceding consecutive hyphenated
lines in the current environment.
\n[.hlm]
The maximum number of consecutive hyphenated lines allowed
in the current environment.
\n[.hy]
The hyphenation mode in the current environment.
\n[.hym]
The hyphenation margin in the current environment.
\n[.hys]
The hyphenation space adjustment threshold in the current
environment.
\n[.in]
The indentation that applies to the current output line.
\n[.int]
Set to a positive value if last output line is interrupted
(i.e., if it contains \c).
\n[.kern]
1 if pairwise kerning is enabled, 0 otherwise.
\n[.lg]
The current ligature mode (as set by the lg request).
\n[.linetabs]
The current line-tabs mode (as set by the linetabs
request).
\n[.ll]
The line length that applies to the current output line.
\n[.lt]
The title length as set by the lt request.
\n[.m] The name of the current drawing color. This is a string-
valued register.
\n[.M] The name of the current background color. This is a
string-valued register.
\n[.ne]
The amount of space that was needed in the last ne request
that caused a trap to be sprung. Useful in conjunction
with the \n[.trunc] register.
\n[.nm]
1 if output line numbering is enabled (even if temporarily
suppressed), 0 otherwise.
\n[.ns]
1 if no-space mode is active, 0 otherwise.
\n[.O] The current output level as set with \O.
\n[.P] 1 if the current page is in the output list set with -o.
\n[.pe]
1 during a page ejection caused by the bp request,
0 otherwise.
\n[.pn]
The number of the next page, either the value set by a pn
request, or the number of the current page plus 1.
\n[.ps]
The current point size in scaled points.
\n[.psr]
The last-requested point size in scaled points.
\n[.pvs]
The current post-vertical line space as set with the pvs
request.
\n[.rj]
The number of lines to be right-justified as set by the rj
request.
\n[.slant]
The slant of the current font as set with \S.
\n[.sr]
The last requested point size in points as a decimal
fraction. This is a string-valued register.
\n[.ss]
\n[.sss]
The values of minimal inter-word spacing and additional
inter-sentence spacing, respectively, in twelfths of the
space width of the current font. Set by the .ss request.
\n[.sty]
The current font style. This is a string-valued register.
\n[.tabs]
A string representation of the current tab settings
suitable for use as an argument to the ta request.
\n[.trunc]
The amount of vertical space truncated by the most
recently sprung vertical position trap, or, if the trap
was sprung by an ne request, minus the amount of vertical
motion produced by the ne request. In other words, at the
point a trap is sprung, it represents the difference of
what the vertical position would have been but for the
trap, and what the vertical position actually is. Useful
in conjunction with the \n[.ne] register.
\n[.U] Set to 1 if in unsafe mode (as determined by troff's -U
command-line option) and 0 otherwise.
\n[.vpt]
1 if vertical position traps are enabled, 0 otherwise.
\n[.warn]
The sum of the numbers associated with each of the
currently enabled warnings. The number associated with
each warning is listed in troff(1).
\n[.x] The major version number of the running troff formatter.
For example, if the version number is 1.23.0, then \n[.x]
contains 1.
\n[.y] The minor version number of the running troff formatter.
For example, if the version number is 1.23.0, then \n[.y]
contains 23.
\n[.Y] The revision number of the running troff formatter. For
example, if the version number is 1.23.0, then \n[.Y]
contains 0.
\n[.zoom]
The zoom value of the current font, in multiples of
1/1000th. Zero if no magnification.
\n[llx]
\n[lly]
\n[urx]
\n[ury]
These four read/write registers are set by the psbb
request and contain the bounding box values (in PostScript
units) of a given PostScript image.
The following read/write registers are set by the \w escape
sequence:
\n[rst]
\n[rsb]
Like the st and sb registers, but take account of the
heights and depths of glyphs.
\n[ssc]
The amount of horizontal space (possibly negative) that
should be added to the last glyph before a subscript.
\n[skw]
How far to right of the center of the last glyph in the \w
argument, the center of an accent from a roman font should
be placed over that glyph.
Other available read/write number registers are:
\n[c.] The current input line number. \n[.c] is a read-only
alias to this register.
\n[hours]
The number of hours past midnight. Initialized at start-
up.
\n[hp] The current horizontal position at input line.
\n[lsn]
\n[lss]
If there are leading spaces on an input line, these
registers hold the count of leading spaces and the amount
of corresponding horizontal motion, respectively.
\n[minutes]
The number of minutes after the hour. Initialized at
start-up.
\n[seconds]
The number of seconds after the minute. Initialized at
start-up.
\n[systat]
The return value of the system() function executed by the
last sy request.
\n[slimit]
If greater than 0, the maximum number of objects on the
input stack. If less than or equal to 0, there is no
limit on the number of objects on the input stack. With
no limit, recursion can continue until virtual memory is
exhausted.
\n[year]
The current year. AT&T troff's \n[yr] register stores the
current year minus 1900.
Miscellaneous
GNU troff predefines a string, \*[.T] containing the argument
given to the -T command-line option, namely the output device
(for example, pdf or utf8). The (read-only) register \n[.T]
interpolates 1 if troff is called with the -T command-line
option, and 0 otherwise.
Fonts not listed in the DESC file are automatically mounted on
the next available font position when they are referenced. If a
font is to be mounted explicitly with the .fp request on an
unused font position, it should be mounted on the first unused
font position, which can be found in the \n[.fp] register;
although troff does not enforce that strictly. Rather, it does
not allow a font to be mounted at a position whose number is much
greater than that of any currently used position.
Interpolating a string does not hide existing macro arguments.
Thus, in a macro, a more efficient way of doing
.xx \\$@
is
\\*[xx]\\
If the font description file contains pairwise kerning
information, glyphs from that font are kerned. Kerning between
two glyphs can be inhibited by placing a non-printing input break
\& between them.
In a string comparison in a condition, characters that appear at
different interpolation depths from the first delimiter character
are not recognized as the second or third delimiters. This also
applies to the .tl request. In a \w escape sequence, a character
that appears at a different interpolation depth from the starting
delimiter character is not recognized as the closing delimiter
character. The same is true for \A, \b, \B, \C, \l, \L, \o, \X,
and \Z. When decoding a macro or string argument that is
delimited by double quotes, a character that appears at a
different interpolation depth from the starting delimiter
character is not recognized as the closing delimiter character.
The implementation of \$@ ensures that the double quotes
surrounding an argument appear at the same interpolation depth,
which is differs from the depth of the argument itself. In a
long escape name ] is not recognized as a closing delimiter
except when it occurs at the same interpolation depth as the
opening [. In compatibility mode, no attention is paid to the
interpolation depth.
In groff, the .tr request can map characters onto \~.
A font can control the widths of spaces emitted by the \| and \^
escape sequences, by defining glyphs of these names (including
the leading backslash).
In groff, tabs and spaces are allowed between the first and
second dots (or between the dot and the name of the ending macro)
that end a macro definition. Example:
.if t \{\
. de bar
. nop Hello, I'm 'bar'.
. .
.\}
