This is groff, produced by makeinfo version 4.2 from ./groff.texinfo.

This manual documents GNU `troff' version 1.18.

   Copyright (C) 1994-2000, 2001, 2002 Free Software Foundation, Inc.

     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.1 or any later version published by the Free Software
     Foundation; with no Invariant Sections, with the Front-Cover texts
     being `A GNU Manual," and with the Back-Cover Texts as in (a)
     below.  A copy of the license is included in the section entitled
     `GNU Free Documentation License."

     (a) The FSF's Back-Cover Text is: `You have freedom to copy and
     modify this GNU Manual, like GNU software.  Copies published by
     the Free Software Foundation raise funds for GNU development."
   
INFO-DIR-SECTION Miscellaneous
START-INFO-DIR-ENTRY
* Groff: (groff).               The GNU troff document formatting system.
END-INFO-DIR-ENTRY


File: groff,  Node: Page Control,  Next: Fonts,  Prev: Page Layout,  Up: gtroff Reference

Page Control
============

 - Request: .bp [page]
 - Request: .bp +page
 - Request: .bp -page
     Stop processing the current page and move to the next page.  This
     request causes a break.  It can also take an argument to set
     (increase, decrease) the page number of the next page.  The only
     difference between `bp' and `pn' is that `pn' does not cause a
     break or actually eject a page.


          .de newpage                         \" define macro
          'bp                                 \" begin page
          'sp .5i                             \" vertical space
          .tl 'left top'center top'right top' \" title
          'sp .3i                             \" vertical space
          ..                                  \" end macro

     `bp' has no effect if not called within the top-level diversion
     (*note Diversions::).

 - Request: .ne [space]
     It is often necessary to force a certain amount of space before a
     new page occurs.  This is most useful to make sure that there is
     not a single "orphan" line left at the bottom of a page.  The `ne'
     request ensures that there is a certain distance, specified by the
     first argument, before the next page is triggered (see *Note
     Traps::, for further information).  The default scaling indicator
     for `ne' is `v'; the default value of SPACE is 1v if no argument
     is given.

     For example, to make sure that no fewer than 2 lines get orphaned,
     do the following before each paragraph:


          .ne 2
          text text text

     `ne' will then automatically cause a page break if there is space
     for one line only.

 - Request: .sv [space]
 - Request: .os
     `sv' is similar to the `ne' request; it reserves the specified
     amount of vertical space.  If the desired amount of space exists
     before the next trap (or the bottom page boundary if no trap is
     set), the space is output immediately (ignoring a partially filled
     line which stays untouched).  If there is not enough space, it is
     stored for later output via the `os' request.  The default value
     is 1v if no argument is given; the default scaling indicator is
     `v'.

     Both `sv' and `os' ignore no-space mode.  While the `sv' request
     allows negative values for SPACE, `os' will ignore them.

 - Register: \n[nl]
     This register contains the current vertical position.  If the
     vertical position is zero and the top of page transition hasn't
     happened yet, `nl' is set to negative value.  `gtroff' itself does
     this at the very beginning of a document before anything has been
     printed, but the main usage is to plant a header trap on a page if
     this page has already started.

     Consider the following:


          .de xxx
          .  sp
          .  tl ''Header''
          .  sp
          ..
          .
          First page.
          .bp
          .wh 0 xxx
          .nr nl (-1)
          Second page.

     Result:


          First page.
          
          ...
          
                                       Header
          
          Second page.
          
          ...

     Without resetting `nl' to a negative value, the just planted trap
     would be active beginning with the _next_ page, not the current
     one.

     *Note Diversions::, for a comparison with the `.h' and `.d'
     registers.


File: groff,  Node: Fonts,  Next: Sizes,  Prev: Page Control,  Up: gtroff Reference

Fonts
=====

   `gtroff' can switch fonts at any point in the text.

   The basic set of fonts is `R', `I', `B', and `BI'.  These are Times
Roman, Italic, Bold, and Bold Italic.  For non-TTY devices, there is
also at least one symbol font which contains various special symbols
(Greek, mathematics).

* Menu:

* Changing Fonts::
* Font Families::
* Font Positions::
* Using Symbols::
* Special Fonts::
* Artificial Fonts::
* Ligatures and Kerning::


File: groff,  Node: Changing Fonts,  Next: Font Families,  Prev: Fonts,  Up: Fonts

Changing Fonts
--------------

 - Request: .ft [font]
 - Escape: \fF
 - Escape: \f(FN
 - Escape: \f[FONT]
     The `ft' request and the `\f' escape change the current font to
     FONT (one-character name F, two-character name FN).

     If FONT is a style name (as set with the `sty' request or with the
     `styles' command in the `DESC' file), use it within the current
     font family (as set with the `fam' request, `\F' escape, or with
     the `family' command in the `DESC' file).

     With no argument or using `P' as an argument, `.ft' switches to
     the previous font.  Use `\f[]' to do this with the escape.  The
     old syntax forms `\fP' or `\f[P]' are also supported.

     Fonts are generally specified as upper-case strings, which are
     usually 1 to 4 characters representing an abbreviation or acronym
     of the font name.  This is no limitation, just a convention.

     The example below produces two identical lines.


          eggs, bacon,
          .ft B
          spam
          .ft
          and sausage.
          
          eggs, bacon, \fBspam\fP and sausage.

     Note that `\f' doesn't produce an input token in `gtroff'.  As a
     consequence, it can be used in requests like `mc' (which expects a
     single character as an argument) to change the font on the fly:


          .mc \f[I]x\f[]

     *Note Font Positions::, for an alternative syntax.

 - Request: .ftr f [g]
     Translate font F to font G.  Whenever a font named F is referred
     to in a `\f' escape sequence, 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 the translation is undone.


File: groff,  Node: Font Families,  Next: Font Positions,  Prev: Changing Fonts,  Up: Fonts

Font Families
-------------

   Due to the variety of fonts available, `gtroff' has added the
concept of "font families" and "font styles".  The fonts are specified
as the concatenation of the font family and style.  Specifying a font
without the family part causes `gtroff' to use that style of the
current family.

   Currently, fonts for the devices `-Tps', `-Tdvi', and `-Tlbp' are
set up to this mechanism.  By default, `gtroff' uses the Times family
with the four styles `R', `I', `B', and `BI'.

   This way, it is possible to use the basic four fonts and to select a
different font family on the command line (*note Groff Options::).

 - Request: .fam [family]
 - Register: \n[.fam]
 - Escape: \FF
 - Escape: \F(FM
 - Escape: \F[FAMILY]
 - Register: \n[.fn]
     Switch font family to FAMILY (one-character name F, two-character
     name FM).  If no argument is given, switch back to the previous
     font family.  Use `\F[]' to do this with the escape.  Note that
     `\FP' doesn't work; it selects font family `P' instead.

     The value at start-up is `T'.  The current font family is
     available in the read-only number register `.fam' (this is a
     string-valued register); it is associated with the current
     environment.


          spam,
          .fam H    \" helvetica family
          spam,     \" used font is family H + style R = HR
          .ft B     \" family H + style B = font HB
          spam,
          .fam T    \" times family
          spam,     \" used font is family T + style B = TB
          .ft AR    \" font AR (not a style)
          baked beans,
          .ft R     \" family T + style R = font TR
          and spam.

     Note that `\F' doesn't produce an input token in `gtroff'.  As a
     consequence, it can be used in requests like `mc' (which expects a
     single character as an argument) to change the font family on the
     fly:


          .mc \F[P]x\F[]

     The `.fn' register contains the current "real font name" of the
     current font.  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.

 - Request: .sty n style
     Associate STYLE 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.  If it is a style, the font that is actually used is the
     font which name 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' will be used.
     If the current font is not a style, then the current family is
     ignored.  If the requests `cs', `bd', `tkf', `uf', or `fspecial'
     are applied to a style, they will instead be applied to the member
     of the current family corresponding to that style.

     N must be a non-negative integer value.

     The default family can be set with the `-f' option (*note Groff
     Options::).  The `styles' command in the `DESC' file controls
     which font positions (if any) are initially associated with styles
     rather than fonts.  For example, the default setting for
     POSTSCRIPT fonts


          styles R I B BI

     is equivalent to


          .sty 1 R
          .sty 2 I
          .sty 3 B
          .sty 4 BI

     `fam' and `\F' always check whether the current font position is
     valid; this can give surprising results if the current font
     position is associated with a style.

     In the following example, we want to access the POSTSCRIPT font
     `FooBar' from the font family `Foo':


          .sty \n[.fp] Bar
          .fam Foo
              => warning: can't find font `FooR'

     The default font position at start-up is 1; for the POSTSCRIPT
     device, this is associated with style `R', so `gtroff' tries to
     open `FooR'.

     A solution to this problem is to use a dummy font like the
     following:


          .fp 0 dummy TR    \" set up dummy font at position 0
          .sty \n[.fp] Bar  \" register style `Bar'
          .ft 0             \" switch to font at position 0
          .fam Foo          \" activate family `Foo'
          .ft Bar           \" switch to font `FooBar'

     *Note Font Positions::.


File: groff,  Node: Font Positions,  Next: Using Symbols,  Prev: Font Families,  Up: Fonts

Font Positions
--------------

   For the sake of old phototypesetters and compatibility with old
versions of `troff', `gtroff' has the concept of font "positions", on
which various fonts are mounted.

 - Request: .fp pos font [external-name]
 - Register: \n[.f]
 - Register: \n[.fp]
     Mount font FONT at position POS (which must be a non-negative
     integer).  This numeric position can then be referred to with font
     changing commands.  When `gtroff' starts it is using font
     position 1 (which must exist; position 0 is unused usually at
     start-up).

     The current font in use, as a font position, is available in the
     read-only number register `.f'.  This can be useful to remember the
     current font for later recall.  It is associated with the current
     environment (*note Environments::).


          .nr save-font \n[.f]
          .ft B
          ... text text text ...
          .ft \n[save-font]

     The number of the next free font position is available in the
     read-only number register `.fp'.  This is useful when mounting a
     new font, like so:


          .fp \n[.fp] NEATOFONT

     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 `.fp' register.  Although
     `gtroff' does not enforce this strictly, it is not allowed to
     mount a font at a position whose number is much greater (approx.
     1000 positions) than that of any currently used position.

     The `fp' request has an optional third argument.  This argument
     gives the external name of the font, which is used for finding the
     font description file.  The second argument gives the internal
     name of the font which is used to refer to the font in `gtroff'
     after it has been mounted.  If there is no third argument then the
     internal name is used as the external name.  This feature makes it
     possible to use fonts with long names in compatibility mode.

   Both the `ft' request and the `\f' escape have alternative syntax
forms to access font positions.

 - Request: .ft nnn
 - Escape: \fN
 - Escape: \f(NN
 - Escape: \f[NNN]
     Change the current font position to NNN (one-digit position N,
     two-digit position NN), which must be a non-negative integer.

     If NNN is associated with a style (as set with the `sty' request
     or with the `styles' command in the `DESC' file), use it within
     the current font family (as set with the `fam' request, the `\F'
     escape, or with the `family' command in the `DESC' file).


          this is font 1
          .ft 2
          this is font 2
          .ft                   \" switch back to font 1
          .ft 3
          this is font 3
          .ft
          this is font 1 again

     *Note Changing Fonts::, for the standard syntax form.


File: groff,  Node: Using Symbols,  Next: Special Fonts,  Prev: Font Positions,  Up: Fonts

Using Symbols
-------------

   A "glyph" is a graphical representation of a "character".  While a
character is an abstract entity containing semantic information, a
glyph is something which can be actually seen on screen or paper.  It
is possible that a character has multiple glyph representation forms
(for example, the character `A' can be either written in a roman or an
italic font, yielding two different glyphs); sometimes more than one
character maps to a single glyph (this is a "ligature" - the most
common is `fi').

   A "symbol" is simply a named glyph.  Within `gtroff', all glyph
names of a particular font are defined in its font file.  If the user
requests a glyph not available in this font, `gtroff' looks up an
ordered list of "special fonts".  By default, the POSTSCRIPT output
device supports the two special fonts `SS' (slanted symbols) and `S'
(symbols) (the former is looked up before the latter).  Other output
devices use different names for special fonts.  Fonts mounted with the
`fonts' keyword in the `DESC' file are globally available.  To install
additional special fonts locally (i.e. for a particular font), use the
`fspecial' request.

   In summary, `gtroff' tries the following to find a given symbol:

   * If the symbol has been defined with the `char' request, use it.
     This hides a symbol with the same name in the current font.

   * Check the current font.

   * If the symbol has been defined with the `fchar' request, use it.

   * Check all fonts given with the `fspecial' request, in the order of
     appearance in `fspecial' calls.

   * Check all fonts given with the `special' request, in the order of
     appearance in `special' calls (inclusively the special fonts
     defined in the `DESC' file, which come first).

   * As a last resort, consult all fonts loaded up to now (in the order
     they have been called the first time) for special fonts and check
     them.

   *Note Font Files::, and *Note Special Fonts::, for more details.

 - Escape: \(NM
 - Escape: \[NAME]
     Insert a symbol NAME (two-character name NM).  There is no special
     syntax for one-character names - the natural form `\N' would
     collide with escapes.(1) (*note Using Symbols-Footnote-1::)

     If NAME is undefined, a warning of type `char' is generated, and
     the escape is ignored.  *Note Debugging::, for information about
     warnings.

     The list of available symbols is device dependent; see the
     `groff_char(7)' man page for a complete list for the given output
     device.  For example, say


          man -Tdvi groff_char > groff_char.dvi

     for a list using the default DVI fonts (not all versions of the
     `man' program support the `-T' option).  If you want to use an
     additional macro package to change the used fonts, `groff' must be
     called directly:


          groff -Tdvi -mec -man groff_char.7 > groff_char.dvi


 - Escape: \C'XXX'
     Typeset the glyph named XXX.(2) (*note Using Symbols-Footnote-2::)
     Normally it is more convenient to use `\[XXX]', but `\C' has the
     advantage that it is compatible with newer versions of AT&T
     `troff' and is available in compatibility mode.

 - Escape: \N'N'
     Typeset the glyph with code N in the current font (`n' is *not*
     the input character code).  The number N can be any non-negative
     decimal integer.  Most devices only have glyphs with codes between
     0 and 255; the Unicode output device uses codes in the range
     0-65535.  If the current font does not contain a glyph with that
     code, special fonts are _not_ searched.  The `\N' escape sequence
     can be conveniently used in conjunction with the `char' request:


          .char \[phone] \f[ZD]\N'37'

     The code of each glyph is given in the fourth column in the font
     description file after the `charset' command.  It is possible to
     include unnamed glyphs in the font description file by using a
     name of `---'; the `\N' escape sequence is the only way to use
     these.

   Some escape sequences directly map onto special glyphs.

 - Escape: \'
     This is a backslash followed by the apostrophe character, ASCII
     character `0x27' (EBCDIC character `0x7D').  The same as `\[aa]',
     the acute accent.

 - Escape: \`
     This is a backslash followed by ASCII character `0x60' (EBCDIC
     character `0x79' usually).  The same as `\[ga]', the grave accent.

 - Escape: \-
     This is the same as `\[-]', the minus sign in the current font.

 - Request: .cflags n c1 c2 ...
     Input characters and symbols have certain properties associated
     with it.(3) (*note Using Symbols-Footnote-3::)  These properties
     can be modified with the `cflags' request.  The first argument is
     the sum of the desired flags and the remaining arguments are the
     characters or symbols to have those properties.  It is possible to
     omit the spaces between the characters or symbols.

    `1'
          The character ends sentences (initially characters `.?!' have
          this property).

    `2'
          Lines can be broken before the character (initially no
          characters have this property).

    `4'
          Lines can be broken after the character (initially the
          character `-' and the symbols `\(hy' and `\(em' have this
          property).

    `8'
          The character overlaps horizontally (initially the symbols
          `\(ul\(rn\(ru' have this property).

    `16'
          The character overlaps vertically (initially symbol `\(br' has
          this property).

    `32'
          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; in other
          words the character is "transparent" for the purposes of
          end-of-sentence recognition - this is the same as having a
          zero space factor in TeX (initially characters `"')]*' and
          the symbols `\(dg\(rq' have this property).

 - Request: .char g [string]
 - Request: .fchar g [string]
     Define a new glyph G to be STRING (which can be empty).(4) (*note
     Using Symbols-Footnote-4::)  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
     being processed.  Any emboldening, constant spacing or track
     kerning is applied to this object rather than to individual
     characters in STRING.

     A glyph 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' or `trin'
     requests; it can be made the leader character by the `lc' request;
     repeated patterns can be drawn with the glyph using the `\l' and
     `\L' escape sequences; words containing the glyph can be
     hyphenated correctly if the `hcode' request is used to give the
     glyph's symbol a hyphenation code.

     There is a special anti-recursion feature: Use of `g' within the
     glyph's definition is handled like normal characters and symbols
     not defined with `char'.

     Note that the `tr' and `trin' requests take precedence if `char'
     accesses the same symbol.


          .tr XY
          X
              => Y
          .char X Z
          X
              => Y
          .tr XX
          X
              => Z

     The `fchar' request defines a fallback glyph: `gtroff' only checks
     for glyphs defined with `fchar' if it cannot find the glyph in the
     current font.  `gtroff' carries out this test before checking
     special fonts.

 - Request: .rchar c1 c2 ...
     Remove the definitions of glyphs C1, C2, .... This undoes the
     effect of a `char' or `fchar' request.

     It is possible to omit the whitespace between arguments.

   *Note Special Characters::.


File: groff,  Node: Using Symbols-Footnotes,  Up: Using Symbols

   (1) Note that a one-character symbol is not the same as an input
character, i.e., the character `a' is not the same as `\[a]'.  By
default, `groff' defines only a single one-character symbol, `\[-]'; it
is usually accessed as `\-'.  On the other hand, `gtroff' has the
special feature that `\[charXXX]' is the same as the input character
with character code XXX.  For example, `\[char97]' is identical to the
letter `a' if ASCII encoding is active.

   (2) `\C' is actually a misnomer since it accesses an output glyph.

   (3) Note that the output glyphs themselves don't have such
properties.  For `gtroff', a glyph is a numbered box with a given
width, depth, and height, nothing else.  All manipulations with the
`cflags' request work on the input level.

   (4) `char' is a misnomer since an output glyph is defined.


File: groff,  Node: Special Fonts,  Next: Artificial Fonts,  Prev: Using Symbols,  Up: Fonts

Special Fonts
-------------

   Special fonts are those that `gtroff' searches when it cannot find
the requested glyph in the current font.  The Symbol font is usually a
special font.

   `gtroff' provides the following two requests to add more special
fonts.  *Note Using Symbols::, for a detailed description of the glyph
searching mechanism in `gtroff'.

   Usually, only non-TTY devices have special fonts.

 - Request: .special s1 s2 ...
 - Request: .fspecial f s1 s2 ...
     Use the `special' request to define special fonts.  They are
     appended to the list of global special fonts in the given order.
     The first entries in this list are the fonts defined with the
     `fonts' command in the `DESC' file which are marked as special in
     the corresponding font description files.

     Use the `fspecial' request to designate special fonts only when
     font F font is active.  They are appended to the list of special
     fonts for F in the given order.  Initially, this list is empty.


File: groff,  Node: Artificial Fonts,  Next: Ligatures and Kerning,  Prev: Special Fonts,  Up: Fonts

Artificial Fonts
----------------

   There are a number of requests and escapes for artificially creating
fonts.  These are largely vestiges of the days when output devices did
not have a wide variety of fonts, and when `nroff' and `troff' were
separate programs.  Most of them are no longer necessary in GNU
`troff'.  Nevertheless, they are supported.

 - Escape: \H'HEIGHT'
 - Escape: \H'+HEIGHT'
 - Escape: \H'-HEIGHT'
     Change (increment, decrement) the height of the current font, but
     not the width.  If HEIGHT is zero, restore the original height.
     Default scaling indicator is `z'.

     Currently, only the `-Tps' device supports this feature.

     Note that `\H' doesn't produce an input token in `gtroff'.  As a
     consequence, it can be used in requests like `mc' (which expects a
     single character as an argument) to change the font on the fly:


          .mc \H'+5z'x\H'0'

     In compatibility mode, `gtroff' behaves differently:  If an
     increment or decrement is used, it is always taken relative to the
     current point size and not relative to the previously selected font
     height.  Thus,


          .cp 1
          \H'+5'test \H'+5'test

     prints the word `test' twice with the same font height (five
     points larger than the current font size).

 - Escape: \S'SLANT'
     Slant the current font by SLANT degrees.  Positive values slant to
     the right.

     Currently, only the `-Tps' device supports this feature.

     Note that `\S' doesn't produce an input token in `gtroff'.  As a
     consequence, it can be used in requests like `mc' (which expects a
     single character as an argument) to change the font on the fly:


          .mc \S'20'x\S'0'

     This request is incorrectly documented in the original UNIX troff
     manual; the slant is always set to an absolute value.

 - Request: .ul [lines]
     The `ul' request normally underlines subsequent lines if a TTY
     output device is used.  Otherwise, the lines are printed in italics
     (only the term `underlined' is used in the following).  The single
     argument is the number of input lines to be underlined; with no
     argument, the next line is underlined.  If LINES is zero or
     negative, stop the effects of `ul' (if it was active).  Requests
     and empty lines do not count for computing the number of underlined
     input lines, even if they produce some output like `tl'.  Lines
     inserted by macros (e.g. invoked by a trap) do count.

     At the beginning of `ul', the current font is stored and the
     underline font is activated.  Within the span of a `ul' request,
     it is possible to change fonts, but after the last line affected by
     `ul' the saved font is restored.

     This number of lines still to be underlined is associated with the
     current environment (*note Environments::).  The underline font
     can be changed with the `uf' request.

     The `ul' request does not underline spaces.

 - Request: .cu [lines]
     The `cu' request is similar to `ul' but underlines spaces as well
     (if a TTY output device is used).

 - Request: .uf font
     Set the underline font (globally) used by `ul' and `cu'.  By
     default, this is the font at position 2.  FONT can be either a
     non-negative font position or the name of a font.

 - Request: .bd font [offset]
 - Request: .bd font1 font2 [offset]
 - Register: \n[.b]
     Artificially create a bold font by printing each glyph twice,
     slightly offset.

     Two syntax forms are available.

        * Imitate a bold font unconditionally.  The first argument
          specifies the font to embolden, and the second is the number
          of basic units, minus one, by which the two glyphs are
          offset.  If the second argument is missing, emboldening is
          turned off.

          FONT can be either a non-negative font position or the name
          of a font.

          OFFSET is available in the `.b' read-only register if a
          special font is active; in the `bd' request, its default unit
          is `u'.

        * Imitate a bold form conditionally.  Embolden FONT1 by OFFSET
          only if font FONT2 is the current font.  This command can be
          issued repeatedly to set up different emboldening values for
          different current fonts.  If the second argument is missing,
          emboldening is turned off for this particular current font.

          This affects special fonts only (either set up with the
          `special' command in font files or with the `fspecial'
          request).

 - Request: .cs font [width [em-size]]
     Switch to and from "constant glyph space mode".  If activated, the
     width of every glyph is WIDTH/36 ems.  The em size is given
     absolutely by EM-SIZE; if this argument is missing, the em value
     is taken from the current font size (as set with the `ps' request)
     when the font is effectively in use.  Without second and third
     argument, constant glyph space mode is deactivated.

     Default scaling indicator for EM-SIZE is `z'; WIDTH is an integer.


File: groff,  Node: Ligatures and Kerning,  Prev: Artificial Fonts,  Up: Fonts

Ligatures and Kerning
---------------------

   Ligatures are groups of characters that are run together, i.e,
producing a single glyph.  For example, the letters `f' and `i' can
form a ligature `fi' as in the word `file'.  This produces a cleaner
look (albeit subtle) to the printed output.  Usually, ligatures are not
available in fonts for TTY output devices.

   Most POSTSCRIPT fonts support the fi and fl ligatures.  The C/A/T
typesetter that was the target of AT&T `troff' also supported `ff',
`ffi', and `ffl' ligatures.  Advanced typesetters or `expert' fonts may
include ligatures for `ft' and `ct', although GNU `troff' does not
support these (yet).

 - Request: .lg [flag]
 - Register: \n[.lg]
     Switch the ligature mechanism on or off; if the parameter is
     non-zero or missing, ligatures are enabled, otherwise disabled.
     Default is on.  The current ligature mode can be found in the
     read-only number register `.lg' (set to 1 or 2 if ligatures are
     enabled, 0 otherwise).

     Setting the ligature mode to 2 enables the two-character ligatures
     (fi, fl, and ff) and disables the three-character ligatures (ffi
     and ffl).

   "Pairwise kerning" is another subtle typesetting mechanism that
modifies the distance between a glyph pair to improve readability.  In
most cases (but not always) the distance is decreased.  Typewriter-like
fonts and fonts for terminals where all glyphs have the same width
don't use kerning.

 - Request: .kern [flag]
 - Register: \n[.kern]
     Switch kerning on or off.  If the parameter is non-zero or missing,
     enable pairwise kerning, otherwise disable it.  The read-only
     number register `.kern' is set to 1 if pairwise kerning is enabled,
     0 otherwise.

     If the font description file contains pairwise kerning information,
     glyphs from that font are kerned.  Kerning between two glyphs can
     be inhibited by placing `\&' between them: `V\&A'.

     *Note Font File Format::.

   "Track kerning" expands or reduces the space between glyphs.  This
can be handy, for example, if you need to squeeze a long word onto a
single line or spread some text to fill a narrow column.  It must be
used with great care since it is usually considered bad typography if
the reader notices the effect.

 - Request: .tkf f s1 n1 s2 n2
     Enable track kerning for font F.  If the current font is F the
     width of every glyph is increased by an amount between N1 and N2
     (N1, N2 can be negative); if the current point size is less than
     or equal to S1 the width is increased by N1; if it is greater than
     or equal to S2 the width is increased by N2; if 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.

     The default scaling indicator is `z' for S1 and S2, `p' for N1 and
     N2.

     Note that the track kerning amount is added even to the rightmost
     glyph in a line; for large values it is thus recommended to
     increase the line length by the same amount to compensate it.

   Sometimes, when typesetting letters of different fonts, more or less
space at such boundaries are needed.  There are two escapes to help
with this.

 - Escape: \/
     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.  Use this escape sequence whenever an
     italic glyph is immediately followed by a roman glyph without any
     intervening space.  This small amount of space is also called
     "italic correction".


 - Escape: \,
     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.  Use this escape sequence
     whenever a roman glyph is immediately followed by an italic glyph
     without any intervening space.  In analogy to above, this space
     could be called "left italic correction", but this term isn't used
     widely.


 - Escape: \&
     Insert a zero-width character, which is invisible.  Its intended
     use is to stop interaction of a character with its surrounding.

        * It prevents the insertion of extra space after an
          end-of-sentence character.


               Test.
               Test.
                   => Test.  Test.
               Test.\&
               Test.
                   => Test. Test.

        * It prevents interpretation of a control character at the
          beginning of an input line.


               .Test
                   => warning: `Test' not defined
               \&.Test
                   => .Test

        * It prevents kerning between two glyphs.

        * It is needed to map an arbitrary character to nothing in the
          `tr' request (*note Character Translations::).

 - Escape: \)
     This escape is similar to `\&' except that it behaves like a
     character declared with the `cflags' request to be transparent for
     the purposes of an end-of-sentence character.

     Its main usage is in macro definitions to protect against arguments
     starting with a control character.


          .de xxx
          \)\\$1
          ..
          .de yyy
          \&\\$1
          ..
          This is a test.\c
          .xxx '
          This is a test.
              =>This is a test.'  This is a test.
          This is a test.\c
          .yyy '
          This is a test.
              =>This is a test.' This is a test.



File: groff,  Node: Sizes,  Next: Strings,  Prev: Fonts,  Up: gtroff Reference

Sizes
=====

   `gtroff' uses two dimensions with each line of text, type size and
vertical spacing.  The "type size" is approximately the height of the
tallest glyph.(1) (*note Sizes-Footnote-1::)  "Vertical spacing" is the
amount of space `gtroff' allows for a line of text; normally, this is
about 20% larger than the current type size.  Ratios smaller than this
can result in hard-to-read text; larger than this, it spreads the text
out more vertically (useful for term papers).  By default, `gtroff'
uses 10 point type on 12 point spacing.

   The difference between type size and vertical spacing is known, by
typesetters, as "leading" (this is pronounced `ledding').

* Menu:

* Changing Type Sizes::
* Fractional Type Sizes::


File: groff,  Node: Sizes-Footnotes,  Up: Sizes

   (1) This is usually the parenthesis.  Note that in most cases the
real dimensions of the glyphs in a font are _not_ related to its type
size!  For example, the standard POSTSCRIPT font families `Times
Roman', `Helvetica', and `Courier' can't be used together at 10pt; to
get acceptable output, the size of `Helvetica' has to be reduced by one
point, and the size of `Courier' must be increased by one point.


File: groff,  Node: Changing Type Sizes,  Next: Fractional Type Sizes,  Prev: Sizes,  Up: Sizes

Changing Type Sizes
-------------------

 - Request: .ps [size]
 - Request: .ps +size
 - Request: .ps -size
 - Escape: \sSIZE
 - Register: \n[.s]
     Use the `ps' request or the `\s' escape to change (increase,
     decrease) the type size (in points).  Specify SIZE as either an
     absolute point size, or as a relative change from the current size.
     The size 0, or no argument, goes back to the previous size.

     Default scaling indicator of `size' is `z'.  If `size' is zero or
     negative, it is set to 1u.

     The read-only number register `.s' returns the point size in
     points as a decimal fraction.  This is a string.  To get the point
     size in scaled points, use the `.ps' register instead.

     `.s' is associated with the current environment (*note
     Environments::).


          snap, snap,
          .ps +2
          grin, grin,
          .ps +2
          wink, wink, \s+2nudge, nudge,\s+8 say no more!
          .ps 10

     The `\s' escape may be called in a variety of ways.  Much like
     other escapes there must be a way to determine where the argument
     ends and the text begins.  Any of the following forms are valid:

    `\sN'
          Set the point size to N points.  N must be either 0 or in the
          range 4 to 39.

    `\s+N'
    `\s-N'
          Increase or decrease the point size by N points.  N must be
          exactly one digit.

    `\s(NN'
          Set the point size to NN points.  NN must be exactly two
          digits.

    `\s+(NN'
    `\s-(NN'
    `\s(+NN'
    `\s(-NN'
          Increase or decrease the point size by NN points.  NN must be
          exactly two digits.

     Note that `\s' doesn't produce an input token in `gtroff'.  As a
     consequence, it can be used in requests like `mc' (which expects a
     single character as an argument) to change the font on the fly:


          .mc \s[20]x\s[0]

     *Note Fractional Type Sizes::, for yet another syntactical form of
     using the `\s' escape.

 - Request: .sizes s1 s2 ... sn [0]
     Some devices may only have certain permissible sizes, in which case
     `gtroff' rounds to the nearest permissible size.  The `DESC' file
     specifies which sizes are permissible for the device.

     Use the `sizes' request to change the permissible sizes for the
     current output device.  Arguments are in scaled points; the
     `sizescale' line in the `DESC' file for the output device provides
     the scaling factor.  For example, if the scaling factor is 1000,
     then the value 12000 is 12 points.

     Each argument can be a single point size (such as `12000'), or a
     range of sizes (such as `4000-72000').  You can optionally end the
     list with a zero.

 - Request: .vs [space]
 - Request: .vs +space
 - Request: .vs -space
 - Register: \n[.v]
     Change (increase, decrease) the vertical spacing by SPACE.  The
     default scaling indicator is `p'.

     If `vs' is called without an argument, the vertical spacing is
     reset to the previous value before the last call to `vs'.

     `gtroff' creates a warning of type `range' if SPACE is zero or
     negative; the vertical spacing is then set to the vertical
     resolution (as given in the `.V' register).

     The read-only number register `.v' contains the current vertical
     spacing; it is associated with the current environment (*note
     Environments::).

   The effective vertical line spacing consists of four components.

   * The vertical line spacing as set with the `vs' request.

   * The "post-vertical line spacing" as set with the `pvs' request.
     This is vertical space which will be added after a line has been
     output.

   * The "extra pre-vertical line space" as set with the `\x' request,
     using a negative value.  This is vertical space which will be
     added once before the current line has been output.

   * The "extra post-vertical line space" as set with the `\x' request,
     using a positive value.  This is vertical space which will be
     added once after the current line has been output.

   It is usually better to use `vs' or `pvs' instead of `ls' to produce
double-spaced documents: `vs' and `pvs' have a finer granularity for
the inserted vertical space compared to `ls'; furthermore, certain
preprocessors assume single-spacing.

   *Note Manipulating Spacing::, for more details on the `\x' escape
and the `ls' request.

 - Request: .pvs [space]
 - Request: .pvs +space
 - Request: .pvs -space
 - Register: \n[.pvs]
     Change (increase, decrease) the post-vertical spacing by SPACE.
     The default scaling indicator is `p'.

     If `pvs' is called without an argument, the post-vertical spacing
     is reset to the previous value before the last call to `pvs'.

     `gtroff' creates a warning of type `range' if SPACE is zero or
     negative; the vertical spacing is then set to zero.

     The read-only number register `.pvs' contains the current
     post-vertical spacing; it is associated with the current
     environment (*note Environments::).


File: groff,  Node: Fractional Type Sizes,  Prev: Changing Type Sizes,  Up: Sizes

Fractional Type Sizes
---------------------

   A "scaled point" is equal to 1/SIZESCALE points, where SIZESCALE is
specified in the `DESC' file (1 by default).  There is a new scale
indicator `z' which has the effect of multiplying by SIZESCALE.
Requests and escape sequences in `gtroff' interpret arguments that
represent a point size as being in units of scaled points, but they
evaluate each such argument using a default scale indicator of `z'.
Arguments treated in this way are the argument to the `ps' request, the
third argument to the `cs' request, the second and fourth arguments to
the `tkf' request, the argument to the `\H' escape sequence, and those
variants of the `\s' escape sequence that take a numeric expression as
their argument (see below).

   For example, suppose SIZESCALE is 1000; then a scaled point is
equivalent to a millipoint; the request `.ps 10.25' is equivalent to
`.ps 10.25z' and thus sets the point size to 10250 scaled points, which
is equal to 10.25 points.

   `gtroff' disallows the use of the `z' scale indicator in instances
where it would make no sense, such as a numeric expression whose
default scale indicator was neither `u' nor `z'.  Similarly it would
make no sense to use a scaling indicator other than `z' or `u' in a
numeric expression whose default scale indicator was `z', and so
`gtroff' disallows this as well.

   There is also new scale indicator `s' which multiplies by the number
of units in a scaled point.  So, for example, `\n[.ps]s' is equal to
`1m'.  Be sure not to confuse the `s' and `z' scale indicators.

 - Register: \n[.ps]
     A read-only number register returning the point size in scaled
     points.

     `.ps' is associated with the current environment (*note
     Environments::).

 - Register: \n[.psr]
 - Register: \n[.sr]
     The last-requested point size in scaled points is contained in the
     `.psr' read-only number register.  The last requested point size
     in points as a decimal fraction can be found in `.sr'.  This is a
     string-valued read-only number register.

     Note that the requested point sizes are device-independent, whereas
     the values returned by the `.ps' and `.s' registers are not.  For
     example, if a point size of 11pt is requested, and a `sizes'
     request (or a `sizescale' line in a `DESC' file) specifies 10.95pt
     instead, this value is actually used.

     Both registers are associated with the current environment (*note
     Environments::).

   The `\s' escape has the following syntax for working with fractional
type sizes:

`\s[N]'
`\s'N''
     Set the point size to N scaled points; N is a numeric expression
     with a default scale indicator of `z'.

`\s[+N]'
`\s[-N]'
`\s+[N]'
`\s-[N]'
`\s'+N''
`\s'-N''
`\s+'N''
`\s-'N''
     Increase or or decrease the point size by N scaled points; N is a
     numeric expression with a default scale indicator of `z'.

   *Note Font Files::.

