path: root/contrib/groff/doc/groff-4

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INFO-DIR-SECTION Miscellaneous
START-INFO-DIR-ENTRY
* Groff: (groff).               The GNU troff document formatting system.
END-INFO-DIR-ENTRY


File: groff,  Node: Manipulating Hyphenation,  Next: Manipulating Spacing,  Prev: Manipulating Filling and Adjusting,  Up: gtroff Reference

Manipulating Hyphenation
========================

   As discussed in *Note Hyphenation::, `gtroff' hyphenates words.
There are a number of ways to influence hyphenation.

 - Request: .hy [mode]
 - Register: \n[.hy]
     Enable hyphenation.  The request has an optional numeric argument,
     MODE, to restrict hyphenation if necessary:

    `1'
          The default argument if MODE is omitted.  Hyphenate without
          restrictions.  This is also the start-up value of `gtroff'.

    `2'
          Do not hyphenate the last word on a page or column.

    `4'
          Do not hyphenate the last two characters of a word.

    `8'
          Do not hyphenate the first two characters of a word.

     Values in the previous table are additive.  For example, the
     value 12 causes `gtroff' to neither hyphenate the last two nor the
     first two characters of a word.

     The current hyphenation restrictions can be found in the read-only
     number register `.hy'.

     The hyphenation mode is associated with the current environment
     (*note Environments::).

 - Request: .nh
     Disable hyphenation (i.e., set the hyphenation mode to zero).  Note
     that the hyphenation mode of the last call to `hy' is not
     remembered.

     The hyphenation mode is associated with the current environment
     (*note Environments::).

 - Request: .hlm [nnn]
 - Register: \n[.hlm]
 - Register: \n[.hlc]
     Set the maximum number of consecutive hyphenated lines to NNN.  If
     this number is negative, there is no maximum.  The default value
     is -1 if NNN is omitted.  This value is associated with the
     current environment (*note Environments::).  Only lines output
     from a given environment count towards the maximum associated with
     that environment.  Hyphens resulting from `\%' are counted;
     explicit hyphens are not.

     The current setting of `hlm' is available in the `.hlm' read-only
     number register.  Also the number of immediately preceding
     consecutive hyphenated lines are available in the read-only number
     register `.hlc'.

 - Request: .hw word1 word2 ...
     Define how WORD1, WORD2, etc. are to be hyphenated.  The words
     must be given with hyphens at the hyphenation points.  For example:


          .hw in-sa-lub-rious

     Besides the space character, any character whose hyphenation code
     value is zero can be used to separate the arguments of `hw' (see
     the documentation for the `hcode' request below for more
     information).  In addition, this request can be used more than
     once.

     Hyphenation exceptions specified with the `hw' request are
     associated with the current hyphenation language; it causes an
     error if there is no current hyphenation language.

     This request is ignored if there is no parameter.

     In old versions of `troff' there was a limited amount of space to
     store such information; fortunately, with `gtroff', this is no
     longer a restriction.

 - Escape: \%
 - Escape: \:
     To tell `gtroff' how to hyphenate words on the fly, use the `\%'
     escape, also known as the "hyphenation character".  Preceding a
     word with this character prevents it from being hyphenated;
     putting it inside a word indicates to `gtroff' that the word may
     be hyphenated at that point.  Note that this mechanism only
     affects that one occurrence of the word; to change the hyphenation
     of a word for the entire document, use the `hw' request.

     The `\:' escape inserts a zero-width break point (that is, the
     word breaks but without adding a hyphen).


          ... check the /var/log/\:httpd/\:access_log file ...

     Note that `\X' and `\Y' start a word, that is, the `\%' escape in
     (say) ` \X'...'\%foobar' and ` \Y'...'\%foobar' no longer prevents
     hyphenation but inserts a hyphenation point at the beginning of
     `foobar'; most likely this isn't what you want to do.

 - Request: .hc [char]
     Change the hyphenation character to CHAR.  This character then
     works the same as the `\%' escape, and thus, no longer appears in
     the output.  Without an argument, `hc' resets the hyphenation
     character to be `\%' (the default) only.

     The hyphenation character is associated with the current
     environment (*note Environments::).

 - Request: .hpf pattern_file
 - Request: .hpfa pattern_file
 - Request: .hpfcode a b [c d ...]
     Read in a file of hyphenation patterns.  This file is searched for
     in the same way as `NAME.tmac' (or `tmac.NAME') is searched for if
     the `-mNAME' option is specified.

     It should have the same format as (simple) TeX patterns 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.

        * No support for `digraphs' like `\$'.

        * `^^XX' (X is 0-9 or a-f) and `^^X' (character code of X in
          the range 0-127) are recognized; other use of `^' causes an
          error.

        * No macro expansion.

        * `hpf' checks for the expression `\patterns{...}' (possibly
          with whitespace before and 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 (only
          recognizing the `%' character as the start of a comment).

     If no `hpf' request is specified (either in the document or in a
     macro package), `gtroff' won't hyphenate at all.

     The `hpfa' request appends a file of patterns to the current list.

     The `hpfcode' request defines mapping values for character codes in
     hyphenation patterns.  `hpf' or `hpfa' then apply the mapping
     (after reading the patterns) before replacing or appending them to
     the current 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.  You can
     use character codes which would be invalid otherwise.

     The set of hyphenation patterns is associated with the current
     language set by the `hla' request.  The `hpf' request is usually
     invoked by the `troffrc' or `troffrc-end' file; by default,
     `troffrc' loads hyphenation patterns for American English (in file
     `hyphen.us').

     A second call to `hpf' (for the same language) will replace the
     hyphenation patterns with the new ones.

     Invoking `hpf' causes an error if there is no current hyphenation
     language.

 - Request: .hcode c1 code1 c2 code2 ...
     Set the hyphenation code of character C1 to CODE1, that of C2 to
     CODE2, etc.  A hyphenation code must be a single input character
     (not a special character) other than a digit or a space.
     Initially each lower-case letter (`a'-`z') has its hyphenation
     code set to itself, and each upper-case letter (`A'-`Z') has a
     hyphenation code which is the lower-case version of itself.

     This request is ignored if it has no parameter.

 - Request: .hym [length]
 - Register: \n[.hym]
     Set the (right) hyphenation margin to LENGTH.  If the current
     adjustment mode is not `b' or `n', the line is not hyphenated if
     it is shorter than LENGTH.  Without an argument, the hyphenation
     margin is reset to its default value, which is 0.  The default
     scaling indicator for this request is `m'.  The hyphenation margin
     is associated with the current environment (*note Environments::).

     A negative argument resets the hyphenation margin to zero, emitting
     a warning of type `range'.

     The current hyphenation margin is available in the `.hym' read-only
     number register.

 - Request: .hys [hyphenation_space]
 - Register: \n[.hys]
     Set the hyphenation space to HYPHENATION_SPACE.  If the current
     adjustment mode is `b' or `n', don't hyphenate the line if it can
     be justified by adding no more than HYPHENATION_SPACE extra space
     to each word space.  Without argument, the hyphenation space is
     set to its default value, which is 0.  The default scaling
     indicator for this request is `m'.  The hyphenation space is
     associated with the current environment (*note Environments::).

     A negative argument resets the hyphenation space to zero, emitting
     a warning of type `range'.

     The current hyphenation space is available in the `.hys' read-only
     number register.

 - Request: .shc [glyph]
     Set the "soft hyphen character" to GLYPH.(1) (*note Manipulating
     Hyphenation-Footnote-1::)  If the argument is omitted, the soft
     hyphen character is set to the default glyph `\(hy' (this is the
     start-up value of `gtroff' also).  The soft hyphen character is
     the glyph that is inserted when a word is hyphenated at a line
     break.  If the soft hyphen character does not exist in the font of
     the character immediately preceding a potential break point, then
     the line is not broken at that point.  Neither definitions
     (specified with the `char' request) nor translations (specified
     with the `tr' request) are considered when finding the soft hyphen
     character.

 - Request: .hla language
 - Register: \n[.hla]
     Set the current hyphenation language to the string LANGUAGE.
     Hyphenation exceptions specified with the `hw' request and
     hyphenation patterns specified with the `hpf' and `hpfa' requests
     are both associated with the current hyphenation language.  The
     `hla' request is usually invoked by the `troffrc' or the
     `troffrc-end' files; `troffrc' sets the default language to `us'.

     The current hyphenation language is available as a string in the
     read-only number register `.hla'.


          .ds curr_language \n[.hla]
          \*[curr_language]
              => us



File: groff,  Node: Manipulating Hyphenation-Footnotes,  Up: Manipulating Hyphenation

   (1) "Soft hyphen character" is a misnomer since it is an output
glyph.


File: groff,  Node: Manipulating Spacing,  Next: Tabs and Fields,  Prev: Manipulating Hyphenation,  Up: gtroff Reference

Manipulating Spacing
====================

 - Request: .sp [distance]
     Space downwards DISTANCE.  With no argument it advances 1 line.  A
     negative argument causes `gtroff' to move up the page the
     specified distance.  If the argument is preceded by a `|' then
     `gtroff' moves that distance from the top of the page.  This
     request causes a line break.  The default scaling indicator is `v'.

 - Request: .ls [nnn]
 - Register: \n[.L]
     Output NNN-1 blank lines after each line of text.  With no
     argument, `gtroff' uses the previous value before the last `ls'
     call.


          .ls 2    \" This causes double-spaced output
          .ls 3    \" This causes triple-spaced output
          .ls      \" Again double-spaced

     The line spacing is associated with the current environment (*note
     Environments::).

     The read-only number register `.L' contains the current line
     spacing setting.

   *Note Changing Type Sizes::, for the requests `vs' and `pvs' as
alternatives to `ls'.

 - Escape: \x'SPACING'
 - Register: \n[.a]
     Sometimes, extra vertical spacing is only needed occasionally, e.g.
     to allow space for a tall construct (like an equation).  The `\x'
     escape does this.  The escape is given a numerical argument,
     usually enclosed in quotes (like `\x'3p''); the default scaling
     indicator is `v'.  If this number is positive extra vertical space
     is inserted below the current line.  A negative number adds space
     above.  If this escape is used multiple times on the same line,
     the maximum of the values is used.

     *Note Escapes::, for details on parameter delimiting characters.

     The `.a' read-only number register contains the most recent
     (nonnegative) extra vertical line space.

     Using `\x' can be necessary in combination with the `\b' escape,
     as the following example shows.


          This is a test with the \[rs]b escape.
          .br
          This is a test with the \[rs]b escape.
          .br
          This is a test with \b'xyz'\x'-1m'\x'1m'.
          .br
          This is a test with the \[rs]b escape.
          .br
          This is a test with the \[rs]b escape.

     produces


          This is a test with the \b escape.
          This is a test with the \b escape.
                              x
          This is a test with y.
                              z
          This is a test with the \b escape.
          This is a test with the \b escape.


 - Request: .ns
 - Request: .rs
 - Register: \n[.ns]
     Enable "no-space mode".  In this mode, spacing (either via `sp' or
     via blank lines) is disabled.  The `bp' request to advance to the
     next page is also disabled, except if it is accompanied by a page
     number (see *Note Page Control::, for more information).  This
     mode ends when actual text is output or the `rs' request is
     encountered which ends no-space mode.  The read-only number
     register `.ns' is set to 1 as long as no-space mode is active.

     This request is useful for macros that conditionally insert
     vertical space before the text starts (for example, a paragraph
     macro could insert some space except when it is the first
     paragraph after a section header).


File: groff,  Node: Tabs and Fields,  Next: Character Translations,  Prev: Manipulating Spacing,  Up: gtroff Reference

Tabs and Fields
===============

   A tab character (ASCII char 9, EBCDIC char 5) causes a horizontal
movement to the next tab stop (much like it did on a typewriter).

 - Escape: \t
     This escape is a non-interpreted tab character.  In copy mode
     (*note Copy-in Mode::), `\t' is the same as a real tab character.

 - Request: .ta [n1 n2 ... nn T r1 r2 ... rn]
 - Register: \n[.tabs]
     Change tab stop positions.  This request takes a series of tab
     specifiers as arguments (optionally divided into two groups with
     the letter `T') which indicate where each tab stop is to be
     (overriding any previous settings).

     Tab stops can be specified absolutely, i.e., as the distance from
     the left margin.  For example, the following sets 6 tab stops every
     one inch.


          .ta 1i 2i 3i 4i 5i 6i

     Tab stops can also be specified using a leading `+' which means
     that the specified tab stop is set relative to the previous tab
     stop.  For example, the following is equivalent to the previous
     example.


          .ta 1i +1i +1i +1i +1i +1i

     `gtroff' supports an extended syntax to specify repeat values after
     the `T' mark (these values are always taken as relative) - this is
     the usual way to specify tabs set at equal intervals.  The
     following is, yet again, the same as the previous examples.  It
     does even more since it defines an infinite number of tab stops
     separated by one inch.


          .ta T 1i

     Now we are ready to interpret the full syntax given at the
     beginning: Set tabs at positions N1, N2, ..., NN and then set tabs
     at NN+R1, NN+R2, ..., NN+RN and then at NN+RN+R1, NN+RN+R2, ...,
     NN+RN+RN, and so on.

     Example: `4c +6c T 3c 5c 2c' is equivalent to `4c 10c 13c 18c 20c
     23c 28c 30c ...'.

     The material in each tab column (i.e., the column between two tab
     stops) may be justified to the right or left or centered in the
     column.  This is specified by appending `R', `L', or `C' to the tab
     specifier.  The default justification is `L'.  Example:


          .ta 1i 2iC 3iR

     Some notes:

        * The default unit of the `ta' request is `m'.

        * A tab stop is converted into a non-breakable horizontal
          movement which can be neither stretched nor squeezed.  For
          example,


               .ds foo a\tb\tc
               .ta T 5i
               \*[foo]

          creates a single line which is a bit longer than 10 inches (a
          string is used to show exactly where the tab characters are).
          Now consider the following:


               .ds bar a\tb b\tc
               .ta T 5i
               \*[bar]

          `gtroff' first converts the tab stops of the line into
          unbreakable horizontal movements, then splits the line after
          the second `b' (assuming a sufficiently short line length).
          Usually, this isn't what the user wants.

        * Superfluous tabs (i.e., tab characters which do not
          correspond to a tab stop) are ignored except the first one
          which delimits the characters belonging to the last tab stop
          for right-justifying or centering.  Consider the following
          example


               .ds Z   foo\tbar\tfoo
               .ds ZZ  foo\tbar\tfoobar
               .ds ZZZ foo\tbar\tfoo\tbar
               .ta 2i 4iR
               \*[Z]
               .br
               \*[ZZ]
               .br
               \*[ZZZ]
               .br

          which produces the following output:


               foo                 bar              foo
               foo                 bar           foobar
               foo                 bar              foobar

          The first line right-justifies the second `foo' relative to
          the tab stop.  The second line right-justifies `foobar'.  The
          third line finally right-justifies only `foo' because of the
          additional tab character which marks the end of the string
          belonging to the last defined tab stop.

        * Tab stops are associated with the current environment (*note
          Environments::).

        * Calling `ta' without an argument removes all tab stops.

        * The start-up value of `gtroff' is `T 0.5i' in troff mode and
          `T 0.8i' in nroff mode (the latter is done with an explicit
          call to the `ta' request in the file `tty.tmac'.

     The read-only number register `.tabs' contains a string
     representation of the current tab settings suitable for use as an
     argument to the `ta' request.


          .ds tab-string \n[.tabs]
          \*[tab-string]
              => T120u

     The `troff' version of the Plan 9 operating system uses register
     `.S' for the same purpose.

 - Request: .tc [fill-glyph]
     Normally `gtroff' fills the space to the next tab stop with
     whitespace.  This can be changed with the `tc' request.  With no
     argument `gtroff' reverts to using whitespace, which is the
     default.  The value of this "tab repetition character" is
     associated with the current environment (*note Environments::).(1)
     (*note Tabs and Fields-Footnote-1::)

 - Request: .linetabs n
 - Register: \n[.linetabs]
     If N is missing or not zero, enable "line-tabs" mode, or disable
     it otherwise (the default).  In line-tabs mode, `gtroff' computes
     tab distances relative to the (current) output line instead of the
     input line.

     For example, the following code:


          .ds x a\t\c
          .ds y b\t\c
          .ds z c
          .ta 1i 3i
          \*x
          \*y
          \*z

     in normal mode, results in the output


          a         b         c

     in line-tabs mode, the same code outputs


          a         b                   c

     Line-tabs mode is associated with the current environment.  The
     read-only register `.linetabs' is set to 1 if in line-tabs mode,
     and 0 in normal mode.

* Menu:

* Leaders::
* Fields::


File: groff,  Node: Tabs and Fields-Footnotes,  Up: Tabs and Fields

   (1) "Tab repetition character" is a misnomer since it is an output
glyph.


File: groff,  Node: Leaders,  Next: Fields,  Prev: Tabs and Fields,  Up: Tabs and Fields

Leaders
-------

   Sometimes it may may be desirable to use the `tc' request to fill a
particular tab stop with a given glyph (for example dots in a table of
contents), but also normal tab stops on the rest of the line.  For this
`gtroff' provides an alternate tab mechanism, called "leaders" which
does just that.

   A leader character (character code 1) behaves similarly to a tab
character: It moves to the next tab stop.  The only difference is that
for this movement, the fill glyph defaults to a period character and
not to space.

 - Escape: \a
     This escape is a non-interpreted leader character.  In copy mode
     (*note Copy-in Mode::), `\a' is the same as a real leader
     character.

 - Request: .lc [fill-glyph]
     Declare the "leader repetition character".(1) (*note
     Leaders-Footnote-1::) Without an argument, leaders act the same as
     tabs (i.e., using whitespace for filling).  `gtroff''s start-up
     value is a dot (`.').  The value of the leader repetition
     character is associated with the current environment (*note
     Environments::).

   For a table of contents, to name an example, tab stops may be
defined so that the section number is one tab stop, the title is the
second with the remaining space being filled with a line of dots, and
then the page number slightly separated from the dots.


     .ds entry 1.1\tFoo\a\t12
     .lc .
     .ta 1i 5i +.25i
     \*[entry]

This produces


     1.1  Foo..........................................  12


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

   (1) "Leader repetition character" is a misnomer since it is an
output glyph.


File: groff,  Node: Fields,  Prev: Leaders,  Up: Tabs and Fields

Fields
------

   "Fields" are a more general way of laying out tabular data.  A field
is defined as the data between a pair of "delimiting characters".  It
contains substrings which are separated by "padding characters".  The
width of a field is the distance on the _input_ line from the position
where the field starts to the next tab stop.  A padding character
inserts stretchable space similar to TeX's `\hss' command (thus it can
even be negative) to make the sum of all substring lengths plus the
stretchable space equal to the field width.  If more than one padding
character is inserted, the available space is evenly distributed among
them.

 - Request: .fc [delim-char [padding-char]]
     Define a delimiting and a padding character for fields.  If the
     latter is missing, the padding character defaults to a space
     character.  If there is no argument at all, the field mechanism is
     disabled (which is the default).  Note that contrary to e.g. the
     tab repetition character, delimiting and padding characters are
     _not_ associated to the current environment (*note Environments::).

     Example:


          .fc # ^
          .ta T 3i
          #foo^bar^smurf#
          .br
          #foo^^bar^smurf#

     and here the result:


          foo         bar          smurf
          foo            bar       smurf



File: groff,  Node: Character Translations,  Next: Troff and Nroff Mode,  Prev: Tabs and Fields,  Up: gtroff Reference

Character Translations
======================

   The control character (`.') and the no-break control character (`'')
can be changed with the `cc' and `c2' requests, respectively.

 - Request: .cc [c]
     Set the control character to C.  With no argument the default
     control character `.' is restored.  The value of the control
     character is associated with the current environment (*note
     Environments::).

 - Request: .c2 [c]
     Set the no-break control character to C.  With no argument the
     default control character `'' is restored.  The value of the
     no-break control character is associated with the current
     environment (*note Environments::).

 - Request: .eo
     Disable the escape mechanism completely.  After executing this
     request, the backslash character `\' no longer starts an escape
     sequence.

     This request can be very helpful in writing macros since it is not
     necessary then to double the escape character.  Here an example:


          .\" This is a simplified version of the
          .\" .BR request from the man macro package
          .eo
          .de BR
          .  ds result \&
          .  while (\n[.$] >= 2) \{\
          .    as result \fB\$1\fR\$2
          .    shift 2
          .  \}
          .  if \n[.$] .as result \fB\$1
          \*[result]
          .  ft R
          ..
          .ec


 - Request: .ec [c]
     Set the escape character to C.  With no argument the default
     escape character `\' is restored.  It can be also used to
     re-enable the escape mechanism after an `eo' request.

     Note that changing the escape character globally will likely break
     macro packages since `gtroff' has no mechanism to `intern' macros,
     i.e., to convert a macro definition into an internal form which is
     independent of its representation (TeX has this mechanism).  If a
     macro is called, it is executed literally.

 - Request: .ecs
 - Request: .ecr
     The `ecs' request saves the current escape character in an
     internal register.  Use this request in combination with the `ec'
     request to temporarily change the escape character.

     The `ecr' request restores the escape character saved with `ecs'.
     Without a previous call to `ecs', this request sets the escape
     character to `\'.

 - Escape: \\
 - Escape: \e
 - Escape: \E
     Print the current escape character (which is the backslash
     character `\' by default).

     `\\' is a `delayed' backslash; more precisely, it is the default
     escape character followed by a backslash, which no longer has
     special meaning due to the leading escape character.  It is _not_
     an escape sequence in the usual sense!  In any unknown escape
     sequence `\X' the escape character is ignored and X is printed.
     But if X is equal to the current escape character, no warning is
     emitted.

     As a consequence, only at top-level or in a diversion a backslash
     glyph is printed; in copy-in mode, it expands to a single
     backslash which then combines with the following character to an
     escape sequence.

     The `\E' escape differs from `\e' by printing an escape character
     that is not interpreted in copy mode.  Use this to define strings
     with escapes that work when used in copy mode (for example, as a
     macro argument).  The following example defines strings to begin
     and end a superscript:


          .ds { \v'-.3m'\s'\Es[.s]*60/100'
          .ds } \s0\v'.3m'

     Another example to demonstrate the differences between the various
     escape sequences, using a strange escape character, `-'.


          .ec -
          .de xxx
          --A'123'
          ..
          .xxx
              => -A'foo'

     The result is surprising for most users, expecting `1' since `foo'
     is a valid identifier.  What has happened?  As mentioned above,
     the leading escape character makes the following character
     ordinary.  Written with the default escape character the sequence
     `--' becomes `\-' - this is the minus sign.

     If the escape character followed by itself is a valid escape
     sequence, only `\E' yields the expected result:


          .ec -
          .de xxx
          -EA'123'
          ..
          .xxx
              => 1


 - Escape: \.
     Similar to `\\', the sequence `\.' isn't a real escape sequence.
     As before, a warning message is suppressed if the escape character
     is followed by a dot, and the dot itself is printed.


          .de foo
          .  nop foo
          .
          .  de bar
          .    nop bar
          \\..
          .
          ..
          .foo
          .bar
              => foo bar

     The first backslash is consumed while the macro is read, and the
     second is swallowed while exexuting macro `foo'.

   A "translation" is a mapping of an input character to an output
glyph.  The mapping occurs at output time, i.e., the input character
gets assigned the metric information of the mapped output character
right before input tokens are converted to nodes (*note Gtroff
Internals::, for more on this process).

 - Request: .tr abcd...
 - Request: .trin abcd...
     Translate character A to glyph B, character C to glyph D, etc.  If
     there is an odd number of arguments, the last one is translated to
     an unstretchable space (`\ ').

     The `trin' request is identical to `tr', but when you unformat a
     diversion with `asciify' it ignores the translation.  *Note
     Diversions::, for details about the `asciify' request.

     Some notes:

        * Special characters (`\(XX', `\[XXX]', `\C'XXX'', `\'', `\`',
          `\-', `\_'), glyphs defined with the `char' request, and
          numbered glyphs (`\N'XXX'') can be translated also.

        * The `\e' escape can be translated also.

        * Characters can be mapped onto the `\%' and `\~' escapes (but
          `\%' and `\~' can't be mapped onto another glyph).

        * The following characters can't be translated: space (with one
          exception, see below), backspace, newline, leader (and `\a'),
          tab (and `\t').

        * Translations are not considered for finding the soft hyphen
          character set with the `shc' request.

        * The pair `C\&' (this is an arbitrary character C followed by
          the zero width space character) maps this character to
          nothing.


               .tr a\&
               foo bar
                   => foo br

          It is even possible to map the space character to nothing:


               .tr aa \&
               foo bar
                   => foobar

          As shown in the example, the space character can't be the
          first character/glyph pair as an argument of `tr'.
          Additionally, it is not possible to map the space character
          to any other glyph; requests like `.tr aa x' undo `.tr aa \&'
          instead.

          If justification is active, lines are justified in spite of
          the `empty' space character (but there is no minimal
          distance, i.e. the space character, between words).

        * After an output glyph has been constructed (this happens at
          the moment immediately before the glyph is appended to an
          output glyph list, either by direct output, in a macro,
          diversion, or string), it is no longer affected by `tr'.

        * Translating character to glyphs where one of them or both are
          undefined is possible also; `tr' does not check whether the
          entities in its argument do exist.

          *Note Gtroff Internals::.

        * `troff' no longer has a hard-coded dependency on Latin-1; all
          `charXXX' entities have been removed from the font
          description files.  This has a notable consequence which
          shows up in warnings like `can't find character with input
          code XXX' if the `tr' request isn't handled properly.

          Consider the following translation:


               .tr e'E'

          This maps input character `e'' onto glyph `E'', which is
          identical to glyph `char201'.  But this glyph intentionally
          doesn't exist!  Instead, `\[char201]' is treated as an input
          character entity and is by default mapped onto `\['E]', and
          `gtroff' doesn't handle translations of translations.

          The right way to write the above translation is


               .tr e'\['E]

          With other words, the first argument of `tr' should be an
          input character or entity, and the second one a glyph entity.

        * Without an argument, the `tr' request is ignored.

 - Request: .trnt abcd...
     `trnt' is the same as the `tr' request except that the
     translations do not apply to text that is transparently throughput
     into a diversion with `\!'.  *Note Diversions::, for more
     information.

     For example,


          .tr ab
          .di x
          \!.tm a
          .di
          .x

     prints `b' to the standard error stream; if `trnt' is used instead
     of `tr' it prints `a'.


File: groff,  Node: Troff and Nroff Mode,  Next: Line Layout,  Prev: Character Translations,  Up: gtroff Reference

Troff and Nroff Mode
====================

   Originally, `nroff' and `troff' were two separate programs, the
former for TTY output, the latter for everything else.  With GNU
`troff', both programs are merged into one executable, sending its
output to a device driver (`grotty' for TTY devices, `grops' for
POSTSCRIPT, etc.) which interprets the intermediate output of `gtroff'.
For UNIX `troff' it makes sense to talk about "Nroff mode" and "Troff
mode" since the differences are hardcoded.  For GNU `troff', this
distinction is not appropriate because `gtroff' simply takes the
information given in the font files for a particular device without
handling requests specially if a TTY output device is used.

   Usually, a macro package can be used with all output devices.
Nevertheless, it is sometimes necessary to make a distinction between
TTY and non-TTY devices: `gtroff' provides two built-in conditions `n'
and `t' for the `if', `ie', and `while' requests to decide whether
`gtroff' shall behave like `nroff' or like `troff'.

 - Request: .troff
     Make the `t' built-in condition true (and the `n' built-in
     condition false) for `if', `ie', and `while' conditional requests.
     This is the default if `gtroff' (_not_ `groff') is started with
     the `-R' switch to avoid loading of the start-up files `troffrc'
     and `troffrc-end'.  Without `-R', `gtroff' stays in troff mode if
     the output device is not a TTY (e.g. `ps').

 - Request: .nroff
     Make the `n' built-in condition true (and the `t' built-in
     condition false) for `if', `ie', and `while' conditional requests.
     This is the default if `gtroff' uses a TTY output device; the
     code for switching to nroff mode is in the file `tty.tmac' which
     is loaded by the start-up file `troffrc'.

   *Note Conditionals and Loops::, for more details on built-in
conditions.


File: groff,  Node: Line Layout,  Next: Line Control,  Prev: Troff and Nroff Mode,  Up: gtroff Reference

Line Layout
===========

   The following drawing shows the dimensions which `gtroff' uses for
placing a line of output onto the page.  They are labeled with the
request which manipulates each dimension.


                     -->| in |<--
                        |<-----------ll------------>|
                   +----+----+----------------------+----+
                   |    :    :                      :    |
                   +----+----+----------------------+----+
                -->| po |<--
                   |<--------paper width---------------->|

These dimensions are:

`po'
     "Page offset" - this is the leftmost position of text on the final
     output, defining the "left margin".

`in'
     "Indentation" - this is the distance from the left margin where
     text is printed.

`ll'
     "Line length" - this is the distance from the left margin to right
     margin.

   A simple demonstration:


     .ll 3i
     This is text without indentation.
     The line length has been set to 3\~inch.
     .in +.5i
     .ll -.5i
     Now the left and right margins are both increased.
     .in
     .ll
     Calling .in and .ll without parameters restore
     the previous values.

   Result:


     This  is text without indenta-
     tion.   The  line  length  has
     been set to 3 inch.
          Now   the  left  and
          right  margins   are
          both increased.
     Calling  .in  and  .ll without
     parameters restore the  previ-
     ous values.

 - Request: .po [offset]
 - Request: .po +offset
 - Request: .po -offset
 - Register: \n[.o]
     Set horizontal page offset to OFFSET (or increment or decrement
     the current value by OFFSET).  Note that this request does not
     cause a break, so changing the page offset in the middle of text
     being filled may not yield the expected result.  The initial value
     is 1i.  For TTY output devices, it is set to 0 in the startup file
     `troffrc'; the default scaling indicator is `m' (and not `v' as
     incorrectly documented in the original UNIX troff manual).

     The current page offset can be found in the read-only number
     register `.o'.

     If `po' is called without an argument, the page offset is reset to
     the previous value before the last call to `po'.


          .po 3i
          \n[.o]
              => 720
          .po -1i
          \n[.o]
              => 480
          .po
          \n[.o]
              => 720


 - Request: .in [indent]
 - Request: .in +indent
 - Request: .in -indent
 - Register: \n[.i]
     Set indentation to INDENT (or increment or decrement the current
     value by INDENT).  This request causes a break.  Initially, there
     is no indentation.

     If `in' is called without an argument, the indentation is reset to
     the previous value before the last call to `in'.  The default
     scaling indicator is `m'.

     The indentation is associated with the current environment (*note
     Environments::).

     If a negative indentation value is specified (which is not
     allowed), `gtroff' emits a warning of type `range' and sets the
     indentation to zero.

     The effect of `in' is delayed until a partially collected line (if
     it exists) is output.  A temporary indent value is reset to zero
     also.

     The current indentation (as set by `in') can be found in the
     read-only number register `.i'.

 - Request: .ti offset
 - Request: .ti +offset
 - Request: .ti -offset
 - Register: \n[.in]
     Temporarily indent the next output line by OFFSET.  If an
     increment or decrement value is specified, adjust the temporary
     indentation relative to the value set by the `in' request.

     This request causes a break; its value is associated with the
     current environment (*note Environments::).  The default scaling
     indicator is `m'.  A call of `ti' without an argument is ignored.

     If the total indentation value is negative (which is not allowed),
     `gtroff' emits a warning of type `range' and sets the temporary
     indentation to zero.  `Total indentation' is either OFFSET if
     specified as an absolute value, or the temporary plus normal
     indentation, if OFFSET is given as a relative value.

     The effect of `ti' is delayed until a partially collected line (if
     it exists) is output.

     The read-only number register `.in' is the indentation that applies
     to the current output line.

     The difference between `.i' and `.in' is that the latter takes
     into account whether a partially collected line still uses the old
     indentation value or a temporary indentation value is active.

 - Request: .ll [length]
 - Request: .ll +length
 - Request: .ll -length
 - Register: \n[.l]
 - Register: \n[.ll]
     Set the line length to LENGTH (or increment or decrement the
     current value by LENGTH).  Initially, the line length is set to
     6.5i.  The effect of `ll' is delayed until a partially collected
     line (if it exists) is output.  The default scaling indicator is
     `m'.

     If `ll' is called without an argument, the line length is reset to
     the previous value before the last call to `ll'.  If a negative
     line length is specified (which is not allowed), `gtroff' emits a
     warning of type `range' and sets the line length to zero.

     The line length is associated with the current environment (*note
     Environments::).

     The current line length (as set by `ll') can be found in the
     read-only number register `.l'.  The read-only number register
     `.ll' is the line length that applies to the current output line.

     Similar to `.i' and `.in', the difference between `.l' and `.ll'
     is that the latter takes into account whether a partially
     collected line still uses the old line length value.


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

Line Control
============

   It is important to understand how `gtroff' handles input and output
lines.

   Many escapes use positioning relative to the input line.  For
example, this


     This is a \h'|1.2i'test.
     
     This is a
     \h'|1.2i'test.

produces


     This is a   test.
     
     This is a             test.

   The main usage of this feature is to define macros which act exactly
at the place where called.


     .\" A simple macro to underline a word
     .de underline
     .  nop \\$1\l'|0\[ul]'
     ..

In the above example, `|0' specifies a negative distance from the
current position (at the end of the just emitted argument `\$1') back
to the beginning of the input line.  Thus, the `\l' escape draws a line
from right to left.

   `gtroff' makes a difference between input and output line
continuation; the latter is also called "interrupting" a line.

 - Escape: \<RET>
 - Escape: \c
 - Register: \n[.int]
     Continue a line.  `\<RET>' (this is a backslash at the end of a
     line immediately followed by a newline) works on the input level,
     suppressing the effects of the following newline in the input.


          This is a \
          .test
              => This is a .test

     The `|' operator is also affected.

     `\c' works on the output level.  Anything after this escape on the
     same line is ignored, except `\R' which works as usual.  Anything
     before `\c' on the same line will be appended to the current
     partial output line.  The next non-command line after an
     interrupted line counts as a new input line.

     The visual results depend on whether no-fill mode is active.

        * If no-fill mode is active (using the `nf' request), the next
          input text line after `\c' will be handled as a continuation
          of the same input text line.


               .nf
               This is a \c
               test.
                   => This is a test.

        * If fill mode is active (using the `fi' request), a word
          interrupted with `\c' will be continued with the text on the
          next input text line, without an intervening space.


               This is a te\c
               st.
                   => This is a test.


     Note that an intervening control line which causes a break is
     stronger than `\c', flushing out the current partial line in the
     usual way.

     The `.int' register contains a positive value if the last output
     line was interrupted with `\c'; this is associated with the
     current environment (*note Environments::).



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

Page Layout
===========

   `gtroff' provides some very primitive operations for controlling
page layout.

 - Request: .pl [length]
 - Request: .pl +length
 - Request: .pl -length
 - Register: \n[.p]
     Set the "page length" to LENGTH (or increment or decrement the
     current value by LENGTH).  This is the length of the physical
     output page.  The default scaling indicator is `v'.

     The current setting can be found in the read-only number register
     `.p'.

     Note that this only specifies the size of the page, not the top and
     bottom margins.  Those are not set by `gtroff' directly.  *Note
     Traps::, for further information on how to do this.

     Negative `pl' values are possible also, but not very useful: No
     trap is sprung, and each line is output on a single page (thus
     suppressing all vertical spacing).

     If no argument or an invalid argument is given, `pl' sets the page
     length to 11i.

   `gtroff' provides several operations which help in setting up top
and bottom titles (or headers and footers).

 - Request: .tl 'left'center'right'
     Print a "title line".  It consists of three parts: a left
     justified portion, a centered portion, and a right justified
     portion.  The argument separator `'' can be replaced with any
     character not occurring in the title line.  The `%' character is
     replaced with the current page number.  This character can be
     changed with the `pc' request (see below).

     Without argument, `tl' is ignored.

     Some notes:

        * A title line is not restricted to the top or bottom of a page.

        * `tl' prints the title line immediately, ignoring a partially
          filled line (which stays untouched).

        * It is not an error to omit closing delimiters.  For example,
          `.tl /foo' is equivalent to `.tl /foo///': It prints a title
          line with the left justified word `foo'; the centered and
          right justfied parts are empty.

        * `tl' accepts the same parameter delimiting characters as the
          `\A' escape; see *Note Escapes::.

 - Request: .lt [length]
 - Request: .lt +length
 - Request: .lt -length
 - Register: \n[.lt]
     The title line is printed using its own line length, which is
     specified (or incremented or decremented) with the `lt' request.
     Initially, the title line length is set to 6.5i.  If a negative
     line length is specified (which is not allowed), `gtroff' emits a
     warning of type `range' and sets the title line length to zero.
     The default scaling indicator is `m'.  If `lt' is called without
     an argument, the title length is reset to the previous value
     before the last call to `lt'.

     The current setting of this is available in the `.lt' read-only
     number register; it is associated with the current environment
     (*note Environments::).


 - Request: .pn page
 - Request: .pn +page
 - Request: .pn -page
 - Register: \n[.pn]
     Change (increase or decrease) the page number of the _next_ page.
     The only argument is the page number; the request is ignored
     without a parameter.

     The read-only number register `.pn' contains the number of the next
     page: either the value set by a `pn' request, or the number of the
     current page plus 1.

 - Register: \n[%]
     A read-write register holding the current page number.

 - Request: .pc [char]
     Change the page number character (used by the `tl' request) to a
     different character.  With no argument, this mechanism is disabled.
     Note that this doesn't affect the number register `%'.

   *Note Traps::.