\input texinfo   @c -*-texinfo-*-
@c %**start of header (This is for running Texinfo on a region.)
@setfilename  groff
@settitle The GNU Troff Manual
@setchapternewpage odd
@footnotestyle separate
@c %**end of header (This is for running Texinfo on a region.)


@dircategory Miscellaneous
@direntry
* Groff: (groff).   The GNU troff document formatting system.
@end direntry


@smallbook


@iftex
@finalout
@end iftex


@ifinfo
This Info file documents GNU troff version 1.12.

Published by the Free Software Foundation
59 Temple Place, Suite 330
Boston, MA  02111-1307  USA

Copyright (C) 1994, 1999 Free Software Foundation, Inc.

Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

@ignore
Permission is granted to process this file through TeX and print the
results, provided the printed document carries copying permission notice
identical to this one except for the removal of this paragraph (this
paragraph not being relevant to the printed manual).

@end ignore
Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided that the
entire resulting derived work is distributed under the terms of a
permission notice identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that this permission notice may be stated in a translation
approved by the Foundation.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU General Public License'' is included exactly as
in the original, and provided that the entire resulting derived work is
distributed under the terms of a permission notice identical to this
one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU General Public License'' may be
included in a translation approved by the Free Software Foundation
instead of in the original English.
@end ifinfo


@titlepage
@title groff
@subtitle The GNU implementation of @code{groff}
@subtitle Edition 1.12
@subtitle October 1999
@author by Trent A.@w{ }Fisher
@author and the maintainer of groff

@c Include the Distribution inside the titlepage environment so
@c that headings are turned off.  Headings on and off do not work.

@page
@vskip 0pt plus 1filll
Copyright @copyright{} 1994, 1999 Free Software Foundation, Inc.

@sp 2
Version 1.13 of @code{groff}, @*
October 1999
@sp 2
Published by the Free Software Foundation @*
59 Temple Place, Suite 330 @*
Boston, MA  02111-1307  USA


Permission is granted to make and distribute verbatim copies of this
manual provided the copyright notice and this permission notice are
preserved on all copies.

Permission is granted to copy and distribute modified versions of this
manual under the conditions for verbatim copying, provided also that the
section entitled ``GNU General Public License'' is included
exactly as in the original, and provided that the entire resulting
derived work is distributed under the terms of a permission notice
identical to this one.

Permission is granted to copy and distribute translations of this manual
into another language, under the above conditions for modified versions,
except that the section entitled ``GNU General Public License'' may be
included in a translation approved by the Free Software Foundation
instead of in the original English.

Cover art by Etienne Suvasa.
@end titlepage
@page



@node Top, Copying, (dir), (dir)

@ifinfo
This Info file documents groff version 1.13, the GNU implementation of
the troff typesetting system.

This is an in-progress document; contributions, comments, or
contributions are welcome.  Send them to bug-groff@@gnu.org.
@end ifinfo

@menu
* Copying::                     
* Introduction::                
* Invoking groff::              
* Tutorial for Macro Users::    
@ignore
* -man::                        
* -ms::                         
* -me::                         
* -mm::                         
@end ignore
* Programming Tutorial::        
@ignore
* geqn::                        
* gtbl::                        
* gpic::                        
* grap::                        
* grefer::                      
* gsoelim::                     
* Devices::                     
@end ignore
* File formats::                
@ignore
* Installation::                
@end ignore
* Request Index::               
* Register Index::              
@ignore
* String Index::                
* Macro Index::                 
@end ignore
* Program Index::               
* Concept Index::               
@end menu



@node Copying, Introduction, Top, Top
@cindex copying
@unnumbered GNU GENERAL PUBLIC LICENSE
@center Version 2, June 1991

@display
Copyright @copyright{} 1989, 1991 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111, USA

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
@end display

@unnumberedsec Preamble

The licenses for most software are designed to take away your freedom to
share and change it.  By contrast, the GNU General Public License is
intended to guarantee your freedom to share and change free software --
to make sure the software is free for all its users.  This General
Public License applies to most of the Free Software Foundation's
software and to any other program whose authors commit to using it.
(Some other Free Software Foundation software is covered by the GNU
Library General Public License instead.)  You can apply it to your
programs, too.

When we speak of free software, we are referring to freedom, not price.
Our General Public Licenses are designed to make sure that you have the
freedom to distribute copies of free software (and charge for this
service if you wish), that you receive source code or can get it if you
want it, that you can change the software or use pieces of it in new
free programs; and that you know you can do these things.

To protect your rights, we need to make restrictions that forbid anyone
to deny you these rights or to ask you to surrender the rights.  These
restrictions translate to certain responsibilities for you if you
distribute copies of the software, or if you modify it.

For example, if you distribute copies of such a program, whether gratis
or for a fee, you must give the recipients all the rights that you have.
You must make sure that they, too, receive or can get the source code.
And you must show them these terms so they know their rights.

We protect your rights with two steps: (1)@w{ }copyright the software,
and (2)@w{ }offer you this license which gives you legal permission to
copy, distribute and/or modify the software.

Also, for each author's protection and ours, we want to make certain
that everyone understands that there is no warranty for this free
software.  If the software is modified by someone else and passed on, we
want its recipients to know that what they have is not the original, so
that any problems introduced by others will not reflect on the original
authors' reputations.

Finally, any free program is threatened constantly by software patents.
We wish to avoid the danger that redistributors of a free program will
individually obtain patent licenses, in effect making the program
proprietary.  To prevent this, we have made it clear that any patent
must be licensed for everyone's free use or not licensed at all.

The precise terms and conditions for copying, distribution and
modification follow.

@iftex
@unnumberedsec TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end iftex
@ifinfo
@center TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
@end ifinfo

@enumerate 0
@item
This License applies to any program or other work which contains a
notice placed by the copyright holder saying it may be distributed under
the terms of this General Public License.  The ``Program'', below,
refers to any such program or work, and a ``work based on the Program''
means either the Program or any derivative work under copyright law:
that is to say, a work containing the Program or a portion of it, either
verbatim or with modifications and/or translated into another language.
(Hereinafter, translation is included without limitation in the term
``modification''.)  Each licensee is addressed as ``you''.

Activities other than copying, distribution and modification are not
covered by this License; they are outside its scope.  The act of running
the Program is not restricted, and the output from the Program is
covered only if its contents constitute a work based on the Program
(independent of having been made by running the Program).  Whether that
is true depends on what the Program does.

@item
You may copy and distribute verbatim copies of the Program's source code
as you receive it, in any medium, provided that you conspicuously and
appropriately publish on each copy an appropriate copyright notice and
disclaimer of warranty; keep intact all the notices that refer to this
License and to the absence of any warranty; and give any other
recipients of the Program a copy of this License along with the Program.

You may charge a fee for the physical act of transferring a copy, and
you may at your option offer warranty protection in exchange for a fee.

@item
You may modify your copy or copies of the Program or any portion of it,
thus forming a work based on the Program, and copy and distribute such
modifications or work under the terms of Section@w{ }1 above, provided
that you also meet all of these conditions:

@enumerate a
@item
You must cause the modified files to carry prominent notices stating
that you changed the files and the date of any change.

@item
You must cause any work that you distribute or publish, that in whole or
in part contains or is derived from the Program or any part thereof, to
be licensed as a whole at no charge to all third parties under the terms
of this License.

@item
If the modified program normally reads commands interactively when run,
you must cause it, when started running for such interactive use in the
most ordinary way, to print or display an announcement including an
appropriate copyright notice and a notice that there is no warranty (or
else, saying that you provide a warranty) and that users may
redistribute the program under these conditions, and telling the user
how to view a copy of this License.  (Exception: if the Program itself
is interactive but does not normally print such an announcement, your
work based on the Program is not required to print an announcement.)
@end enumerate

These requirements apply to the modified work as a whole.  If
identifiable sections of that work are not derived from the Program, and
can be reasonably considered independent and separate works in
themselves, then this License, and its terms, do not apply to those
sections when you distribute them as separate works.  But when you
distribute the same sections as part of a whole which is a work based on
the Program, the distribution of the whole must be on the terms of this
License, whose permissions for other licensees extend to the entire
whole, and thus to each and every part regardless of who wrote it.

Thus, it is not the intent of this section to claim rights or contest
your rights to work written entirely by you; rather, the intent is to
exercise the right to control the distribution of derivative or
collective works based on the Program.

In addition, mere aggregation of another work not based on the Program
with the Program (or with a work based on the Program) on a volume of a
storage or distribution medium does not bring the other work under the
scope of this License.

@item
You may copy and distribute the Program (or a work based on it, under
Section@w{ }2) in object code or executable form under the terms of
Sections 1 and 2 above provided that you also do one of the following:

@enumerate a
@item
Accompany it with the complete corresponding machine-readable source
code, which must be distributed under the terms of Sections 1 and 2
above on a medium customarily used for software interchange; or,

@item
Accompany it with a written offer, valid for at least three years, to
give any third party, for a charge no more than your cost of physically
performing source distribution, a complete machine-readable copy of the
corresponding source code, to be distributed under the terms of Sections
1 and 2 above on a medium customarily used for software interchange; or,

@item
Accompany it with the information you received as to the offer to
distribute corresponding source code.  (This alternative is allowed only
for noncommercial distribution and only if you received the program in
object code or executable form with such an offer, in accord with
Subsection b above.)
@end enumerate

The source code for a work means the preferred form of the work for
making modifications to it.  For an executable work, complete source
code means all the source code for all modules it contains, plus any
associated interface definition files, plus the scripts used to control
compilation and installation of the executable.  However, as a special
exception, the source code distributed need not include anything that is
normally distributed (in either source or binary form) with the major
components (compiler, kernel, and so on) of the operating system on
which the executable runs, unless that component itself accompanies the
executable.

If distribution of executable or object code is made by offering access
to copy from a designated place, then offering equivalent access to copy
the source code from the same place counts as distribution of the source
code, even though third parties are not compelled to copy the source
along with the object code.

@item
You may not copy, modify, sublicense, or distribute the Program except
as expressly provided under this License.  Any attempt otherwise to
copy, modify, sublicense or distribute the Program is void, and will
automatically terminate your rights under this License.  However,
parties who have received copies, or rights, from you under this License
will not have their licenses terminated so long as such parties remain
in full compliance.

@item
You are not required to accept this License, since you have not signed
it.  However, nothing else grants you permission to modify or distribute
the Program or its derivative works.  These actions are prohibited by
law if you do not accept this License.  Therefore, by modifying or
distributing the Program (or any work based on the Program), you
indicate your acceptance of this License to do so, and all its terms and
conditions for copying, distributing or modifying the Program or works
based on it.

@item
Each time you redistribute the Program (or any work based on the
Program), the recipient automatically receives a license from the
original licensor to copy, distribute or modify the Program subject to
these terms and conditions.  You may not impose any further restrictions
on the recipients' exercise of the rights granted herein.  You are not
responsible for enforcing compliance by third parties to this License.

@item
If, as a consequence of a court judgment or allegation of patent
infringement or for any other reason (not limited to patent issues),
conditions are imposed on you (whether by court order, agreement or
otherwise) that contradict the conditions of this License, they do not
excuse you from the conditions of this License.  If you cannot
distribute so as to satisfy simultaneously your obligations under this
License and any other pertinent obligations, then as a consequence you
may not distribute the Program at all.  For example, if a patent license
would not permit royalty-free redistribution of the Program by all those
who receive copies directly or indirectly through you, then the only way
you could satisfy both it and this License would be to refrain entirely
from distribution of the Program.

If any portion of this section is held invalid or unenforceable under
any particular circumstance, the balance of the section is intended to
apply and the section as a whole is intended to apply in other
circumstances.

It is not the purpose of this section to induce you to infringe any
patents or other property right claims or to contest validity of any
such claims; this section has the sole purpose of protecting the
integrity of the free software distribution system, which is implemented
by public license practices.  Many people have made generous
contributions to the wide range of software distributed through that
system in reliance on consistent application of that system; it is up to
the author/donor to decide if he or she is willing to distribute
software through any other system and a licensee cannot impose that
choice.

This section is intended to make thoroughly clear what is believed to be
a consequence of the rest of this License.

@item
If the distribution and/or use of the Program is restricted in certain
countries either by patents or by copyrighted interfaces, the original
copyright holder who places the Program under this License may add an
explicit geographical distribution limitation excluding those countries,
so that distribution is permitted only in or among countries not thus
excluded.  In such case, this License incorporates the limitation as if
written in the body of this License.

@item
The Free Software Foundation may publish revised and/or new versions of
the General Public License from time to time.  Such new versions will be
similar in spirit to the present version, but may differ in detail to
address new problems or concerns.

Each version is given a distinguishing version number.  If the Program
specifies a version number of this License which applies to it and ``any
later version'', you have the option of following the terms and
conditions either of that version or of any later version published by
the Free Software Foundation.  If the Program does not specify a version
number of this License, you may choose any version ever published by the
Free Software Foundation.

@item
If you wish to incorporate parts of the Program into other free programs
whose distribution conditions are different, write to the author to ask
for permission.  For software which is copyrighted by the Free Software
Foundation, write to the Free Software Foundation; we sometimes make
exceptions for this.  Our decision will be guided by the two goals of
preserving the free status of all derivatives of our free software and
of promoting the sharing and reuse of software generally.

@iftex
@heading NO WARRANTY
@end iftex
@ifinfo
@center NO WARRANTY
@end ifinfo

@item
BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY FOR
THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW@.  EXCEPT WHEN
OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER
EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE@.
THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH
YOU@.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL
NECESSARY SERVICING, REPAIR OR CORRECTION.

@item
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR
DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL
DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM
(INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED
INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF
THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR
OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
@end enumerate

@iftex
@heading END OF TERMS AND CONDITIONS
@end iftex
@ifinfo
@center END OF TERMS AND CONDITIONS
@end ifinfo


@page
@unnumberedsec How to Apply These Terms to Your New Programs

If you develop a new program, and you want it to be of the greatest
possible use to the public, the best way to achieve this is to make it
free software which everyone can redistribute and change under these
terms.

To do so, attach the following notices to the program.  It is safest to
attach them to the start of each source file to most effectively convey
the exclusion of warranty; and each file should have at least the
``copyright'' line and a pointer to where the full notice is found.

@smallexample
@var{one line to give the program's name and an idea of what it does.}
Copyright (C) 19@var{yy} @var{name of author}

This program is free software; you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation; either version 2 of the License, or (at your
option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE@.  See the GNU
General Public License for more details.

You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
59 Temple Place, Suite 330, Boston, MA 02111, USA.
@end smallexample

Also add information on how to contact you by electronic and paper mail.

If the program is interactive, make it output a short notice like this
when it starts in an interactive mode:

@smallexample
Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author}
Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type
`show w'.  This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
@end smallexample

The hypothetical commands @samp{show w} and @samp{show c} should show
the appropriate parts of the General Public License.  Of course, the
commands you use may be called something other than @samp{show w} and
@samp{show c}; they could even be mouse-clicks or menu items---whatever
suits your program.

You should also get your employer (if you work as a programmer) or your
school, if any, to sign a ``copyright disclaimer'' for the program, if
necessary.  Here is a sample; alter the names:

@smallexample
@group
Yoyodyne, Inc., hereby disclaims all copyright
interest in the program `Gnomovision'
(which makes passes at compilers) written 
by James Hacker.

@var{signature of Ty Coon}, 1 April 1989
Ty Coon, President of Vice
@end group
@end smallexample

This General Public License does not permit incorporating your program
into proprietary programs.  If your program is a subroutine library, you
may consider it more useful to permit linking proprietary applications
with the library.  If this is what you want to do, use the GNU Library
General Public License instead of this License.



@node Introduction, Invoking groff, Copying, Top
@chapter Introduction
@cindex introduction

GNU @code{troff} (or @code{groff}) is a system for typesetting
documents.  @code{troff} is very flexible and has been in existence (and
use) for about 3@w{ }decades.  It is quite widespread and firmly
entrenched in the @sc{Unix} community.



@menu
* What Is groff?::              
* History::                     
* groff Capabilities::          
* Macro Packages::              
* Preprocessors::               
* Postprocessors::              
* Credits::                     
@end menu

@node What Is groff?, History, Introduction, Introduction
@section What Is @code{groff}?
@cindex what is @code{groff}?
@cindex @code{groff} -- what is it?


@code{groff} belongs to an older generation of document preparation systems,
which operate more like compilers than the more recent interactive
@dfn{WYSIWYG}@footnote{What You See Is What You Get} systems.  @code{groff}
and its contemporary counterpart, @TeX{}, both work using a @dfn{batch}
paradigm: the input (or @dfn{source}) files are normal text files with
embedded formatting commands.  These files can then be processed by
@code{groff} to produce a typeset document on a variety of devices.

Likewise, @code{groff} should not be confused with a @dfn{word
processor}, since that term connotes an integrated system which includes
an editor and a text formatter.  Also, many word processors follow the
WYSIWYG paradigm which was discussed earlier.

Although WYSIWYG systems may be easier to use, they have a number of
disadvantages compared to @code{troff}:

@itemize @bullet{}
@item
They must be used on a bitmapped display to do any operations on your
document.
@item
Most of the WYSIWYG systems are either non-free or are not very
portable.
@item
@code{troff} is firmly entrenched in all @sc{Unix} systems.
@item
It is difficult to have a wide range of capabilities available within
the confines of a GUI/window system.
@item
It is more difficult to make global changes to a document.
@end itemize

@quotation
``GUIs normally make it simple to accomplish simple actions and
impossible to accomplish complex actions.''  --Doug Gwyn (22/Jun/91 in
@code{comp.unix.wizards})
@end quotation



@node History, groff Capabilities, What Is groff?, Introduction
@section History
@cindex history

@code{troff} can trace its origins back to a formatting program called
@code{runoff} which ran on MIT's CTSS system.  This name came from the
common phrase of the time ``I'll run off a document.''

The first version of @sc{Unix} was developed on a PDP-7 which was
sitting around Bell Labs.  In 1971 the developers wanted to get a PDP-11
for further work on the operating system.  In order to justify the cost
for this system, they proposed that they would implement a document
formatting system for the AT&T patents division.  This first formatting
program was a reimplementation of @code{runoff}.  In accordance with
@sc{Unix}'s penchant for abreviations, it was named @code{roff} (an
abreviation of @code{runoff}).

When they needed a more flexible language, a new version of @code{roff}
called @code{nroff} (``Newer @code{roff}'') was written.  It had a much more
complicated syntax, but provided the basis for all future versions.
When they got a Graphic Systems CAT Phototypesetter, J.@: F.@:
Ossanna wrote a version of @code{nroff} which would drive it.  It was
dubbed @code{troff}, for ``typesetter @code{roff}'', although many people
have speculated that it actually means ``Times @code{roff}'' because of
@code{troff}'s use of the Times font family by default.  As such, the
name @code{troff} is pronounced tee-roff rather than trough.

With @code{troff} came @code{nroff} (they were actually the same program
except for some @samp{#ifdef}s), which was for producing output for line
printers and @sc{ascii} terminals.  It understood everything @code{troff}
did, and ignored the commands which were not applicable (i.e.@: font
changes).

Since there are several things which cannot be done easily in
@code{troff}, work on several preprocessors began.  These programs would
transform certain parts of a document into @code{troff}, which made a
very natural use of pipes in @sc{Unix}.

The @code{eqn} preprocessor allowed mathematical formul@ae{} to be
specified in a much simpler and more intuitive manner.  @code{tbl} is a
preprocessor for formatting tables.  The @code{refer} preprocessor (and
the similar program, @code{bib}) processes citations in a document
according to a bibliographic database.

Unfortunately, Ossanna's @code{troff} was written in PDP-11 assembly
language and produced output specifically for the CAT phototypesetter.
He rewrote it in C, although it was now 7000@w{ }lines of uncommented
code and still dependent on the CAT.  As the CAT became less common, and
was no longer supported by the manufacturer, the need to make it support
other devices became a priority.  However, before this could be done, Ossanna
was killed in an auto accident.

@pindex ditroff
So, Brian Kernighan took on the task of rewriting @code{troff}.  The
newly rewritten version produced a device independent code which was
very easy for postprocessors to read and translate to the appropriate
printer codes.  Also, this new version of @code{troff} (called
@code{ditroff}) had several extensions, which included drawing
functions.

Due to the additional abilities of the new version of @code{troff},
several new preprocessors appeared.  The @code{pic} preprocessor
provides a wide range of drawing functions.  Likewise the @code{ideal}
preprocessor did the same, although via a much different paradigm.  The
@code{grap} preprocessor took specifications for graphs, but, unlike
other preprocessors, produced @code{pic} code.

James Clark began work on a GNU implementation of @code{ditroff} in
early@w{ }1989.  The first version, @code{groff}@w{ }0.3.1, was released
June@w{ }1990.  @code{groff} included:

@itemize @bullet{}
@item
a replacement for @code{ditroff} with many extentions;
@item
the @code{soelim}, @code{pic}, @code{tbl}, and @code{eqn} preprocessors;
@item
postprocessors for @sc{ascii} devices, PostScript, @TeX{} DVI, and X@w{
}windows;
@item
a version of the @code{-me} macros and an implementation of the
@code{-man} macros.
@item
a front-end which could construct the (sometimes painfully long)
pipelines required for all the post- and preprocessors.
@end itemize

GNU @code{troff} also eliminated the need for a separate @code{nroff}
program with a postprocessor which would produce @sc{ascii} output.

Development of GNU @code{troff} progressed rapidly, and saw the
additions of a replacement for @code{refer}, an implementation of the
@code{-ms} and @code{-mm} macros, and a program to deduce how to format
a document (@code{grog}).

It was declared a stable (i.e.@: non beta) package with the release of
version@w{ }1.04 around November@w{ }1991.



@node groff Capabilities, Macro Packages, History, Introduction
@section @code{groff} Capabilities
@cindex @code{groff} capabilities
@cindex capabilities of @code{groff}

So what exactly is @code{groff} capable of doing?  @code{groff} provides
a wide range of low-level text formatting operations.  Using these, you
can perform a wide range of formatting tasks, such as footnotes, table
of contents, multiple columns, etc.  Here's a list of the operations
supported by @code{groff}:

@itemize @bullet{}
@item
text filling, adjusting, and centering
@item
hyphenation
@item
page control
@item
font and character size control
@item
vertical spacing (i.e.@: double spacing)
@item
line length and indenting
@item
macros, strings, diversions, and traps
@item
number registers
@item
tabs, leaders, and fields
@item
input and output conventions and character translation
@item
overstrike, bracket, line drawing, and zero-width functions
@item
local horizontal and vertical motions and the width function
@item
three-part titles
@item
output line numbering
@item
conditional acceptance of input
@item
environment switching
@item
insertions from the standard input
@item
input/output file switching
@item
output and error messages
@end itemize


@node Macro Packages, Preprocessors, groff Capabilities, Introduction
@section Macro Packages
@cindex macro packages

Since @code{groff} provides such low-level facilities, it can be quite
difficult to use by itself.  However, @code{groff} provides a
@dfn{macro} facility which allows you to specify how certain routine
operations (e.g., starting paragraphs, printing headers and footers,
etc.)@: should be done.  These macros can be collected together into a
@dfn{macro package}.  There are a number of macro packages available;
the most common (and the ones described in this manual) are @code{-man},
@code{-me}, @code{-ms}, and @code{-mm}.


@node Preprocessors, Postprocessors, Macro Packages, Introduction
@section Preprocessors
@cindex preprocessors

Although @code{groff} provides most functions needed to format a
document, some operations would be unwieldy (e.g., drawing pictures).
Therefore, programs called preprocessors were written which understand
their own language and produce the necessary groff operations.  These
preprocessors are able to differentiate their own input from the rest of
the document via markers.

To use a preprocessor, @sc{Unix} pipes are used to feed the output from
the preprocessor into @code{groff}.  Any number of preprocessors may be
used on a given document; in this case, the preprocessors are linked
together into one pipeline.  However, in @code{groff}, the user does not
need to construct the pipe, but only to tell @code{groff} what
preprocessors to use.

@code{groff} currently has preprocessors for producing tables
(@code{tbl}), typesetting equations (@code{eqn}), drawing pictures
(@code{pic}), and for processing bibliographies (@code{refer}).  An
associated program which is useful when dealing with preprocessors is
@code{soelim}.

There are other preprocessors in existence, but there are,
unfortunately, no free implementations available.  These are
preprocessors for drawing
pictures (@code{ideal} and @code{gremlin}), for drawing graphs
(@code{grap}), and for drawing chemical structures (@code{chem}).


@node Postprocessors, Credits, Preprocessors, Introduction
@section Postprocessors
@cindex postprocessors

@code{groff} actually produces device independent code which may be fed
into a postprocessor which will produce output for a particular device.
Currently, @code{groff} has postprocessors for PostScript devices,
LaserJet printers, @sc{ascii} terminals, graphics terminals on X@w{
}windows (for previewing), @TeX{} DVI format, and HTML.


@node Credits,  , Postprocessors, Introduction
@section Credits
@cindex credits


Large portions of this manual were taken from existing documents, most
notably, the manual pages for the @code{groff} package by James Clark,
and Eric Allman's papers on the @code{-me} macro package.



@node Invoking groff, Tutorial for Macro Users, Introduction, Top
@chapter Invoking @code{groff}
@cindex invoking @code{groff}
@cindex @code{groff} invocation


This section focuses on how to invoke the @code{groff} front end.  This
front end takes care of the details of constructing the pipeline among
the preprocessors, @code{gtroff} and the postprocessor.

It has become a tradition that GNU programs get the prefix @dfn{g} to
distinguish them from their original counterparts provided by the host
(see @ref{Environment}, for more details).  Thus, for example, @code{geqn}
is GNU @code{eqn}.  On operating systems like Linux or the Hurd, which
don't contain proprietary software, and on MS-DOS/MS-Windows, where
@code{troff} and associated programs are not available at all, this
prefix is omitted since GNU @code{troff} is the only used incarnation of
@code{troff}.  Exception: @code{groff} is never replaced by `roff'.


@menu
* Options::                     
* Environment::                 
* Invocation Examples::         
@end menu

@node Options, Environment, Invoking groff, Invoking groff
@section Options
@cindex options


@pindex groff
@pindex gtroff
@pindex gpic
@pindex geqn
@pindex gtbl
@pindex grefer
@pindex gsoelim
@code{groff} is a front-end to the groff document formatting system.
Normally, it runs the @code{gtroff} program and a postprocessor
appropriate for the selected device.  The default device is @samp{ps}
(but it can be changed when @code{groff} is configured and built).
It can optionally preprocess with any of @code{gpic}, @code{geqn},
@code{gtbl}, @code{grefer}, or @code{gsoelim}.

This section only documents options to the @code{groff} front end.  Many
of the arguments to @code{groff} are passed on to @code{gtroff},
therefore those are also included.
@ignore
Arguments to pre- or postprocessors
can be found in @ref{Invoking gpic}, @ref{Invoking geqn}, @ref{Invoking
gtbl}, @ref{Invoking grefer}, @ref{Invoking gsoelim}, @ref{Invoking
grotty}, @ref{Invoking grops}, @ref{Invoking grohtml}, @ref{Invoking
grodvi}, and @ref{Invoking gxditview}.
@end ignore

The command line format for @code{groff} is:

@example
groff [ -abehilpstvzCENRSVXZ ] [ -F@var{dir} ] [ -m@var{name} ]
      [ -T@var{def} ] [ -f@var{fam} ] [ -w@var{name} ] [ -W@var{name} ]
      [ -M@var{dir} ] [ -d@var{cs} ] [ -r@var{cn} ] [ -n@var{num} ]
      [ -o@var{list} ] [ -P@var{arg} ] [ -L@var{arg} ]
      [ @var{files}@dots{} ]
@end example

The command line format for @code{gtroff} is as follows:

@example
gtroff [ -abivzCER ] [ -w@var{name} ] [ -W@var{name} ] [ -d@var{cs} ]
       [ -f@var{fam} ] [ -m@var{name} ] [ -n@var{num} ]
       [ -o@var{list} ] [ -r@var{cn} ] [ -T@var{name} ]
       [ -F@var{dir} ] [ -M@var{dir} ] [ @var{files}@dots{} ]
@end example

@noindent
As you can see, many of the options to @code{groff} are actually passed
on to @code{gtroff}.

Options without an argument can be grouped behind a single @samp{-}.  A
filename of @samp{-} denotes the standard input.

The @code{grog} command can be used to guess the correct @code{groff}
command to use to format a file.

Here's the description of the command-line options:

@cindex command-line options
@table @samp
@item -h
Print a help message.
@item -e
Preprocess with @code{geqn}.
@item -t
Preprocess with @code{gtbl}.
@item -p
Preprocess with @code{gpic}.
@item -s
Preprocess with @code{gsoelim}.
@item -R
Preprocess with @code{grefer}.  No mechanism is provided for passing
arguments to @code{grefer} because most @code{grefer} options have
equivalent commands which can be included in the file.
@ignore
@xref{grefer}, for more details.
@end ignore

@pindex troffrc
Note that @code{gtroff} also accepts a @samp{-R} option, which is not
accessible via @code{groff}.  This option prevents the loading of the
@file{troffrc} file.
@item -v
Make programs run by @code{groff} print out their version number.
@item -V
Print the pipeline on stdout instead of executing it.
@item -z
Suppress output from @code{gtroff}.  Only error messages will be printed.
@item -Z
Do not postprocess the output of @code{gtroff}.  Normally @code{groff}
will automatically run the appropriate postprocessor.
@item -P@var{arg}
Pass @var{arg} to the postprocessor.  Each argument should be passed
with a separate @samp{-P} option. Note that groff does not prepend
@samp{-} to @var{arg} before passing it to the postprocessor.
@item -l
Send the output to a printer.  The command used for this is specified by
the print command in the device description file.
@item -L@var{arg}
Pass @var{arg} to the spooler.  Each argument should be passed with a
separate @samp{-L} option.  Note that @code{groff} does not prepend a
@samp{-} to @var{arg} before passing it to the spooler.
@item -T@var{dev}
Prepare output for device @var{dev}.  The default device is @samp{ps},
unless changed when @code{groff} was configured and built.
The following are the output devices currently available:
@table @samp
@item ps
For PostScript printers and previewers.
@item dvi
For TeX DVI format.
@item X75
For a 75@dmn{dpi} X11 previewer.
@item X100
For a 100@dmn{dpi} X11 previewer.
@item @sc{ascii}
For typewriter-like devices.
@item latin1
For typewriter-like devices that support the ISO Latin-1 character set.
@item lj4
For an HP LaserJet4-compatible (or other PCL5-compatible) printer.
@item html
To produce HTML output.
@end table

The postprocessor to be used for a device is specified by the
@code{postpro} command in the device description file.  (@xref{Font
Files}, for more info.)  This can be overridden with the @samp{-X}
option.
@item -X
Preview with @code{gxditview} instead of using the usual postprocessor.
This is unlikely to produce good results except with @samp{-Tps}.
@item -N
Don't allow newlines with @code{eqn} delimiters.  This is the same as
the @samp{-N} option in @code{geqn}.
@item -S
Safer mode.  Pass the @samp{-S} option to @code{gpic} and use the
@samp{-msafer} macros with @code{gtroff}.
@item -a
Generate an @sc{ascii} approximation of the typeset output.
@item -b
Print a backtrace with each warning or error message.  This backtrace
should help track down the cause of the error.  The line numbers given
in the backtrace may not always be correct: @code{troff}'s idea of line
numbers gets confused by @code{as} or @code{am} requests.
@item -i
Read the standard input after all the named input files have been
processed.
@item -w@var{name}
Enable warning @var{name}.  Available warnings are described in
@ref{Debugging}.  Multiple @samp{-w} options are allowed.
@item -W@var{name}
Inhibit warning @var{name}.  Multiple @samp{-W} options are allowed.
@item -E
Inhibit all error messages.
@item -C
Enable compatibility mode.  @xref{Implementation Differences}, for the
list of incompatibilites between @code{groff} and traditional Unix
@code{troff}.
@item -d@var{cs}
@itemx -d@var{name}=s
Define @var{c} or @var{name} to be a string @var{s}; @var{c} must be a
one-letter @var{name}.
@item -f@var{fam}
Use @var{fam} as the default font family.
@item -m@var{name}
Read in the file @file{tmac.@var{name}}.  Normally this will be searched
for in @code{groff}'s @file{lib/} directory.
@item -n@var{num}
Number the first page @var{num}.
@item -o@var{list}
Output only pages in @var{list}, which is a comma-separated list of page
ranges; @samp{@var{n}} means print page @var{n}, @samp{@var{m}-@var{n}} means
print every page between @var{m} and @var{n}, @samp{-@var{n}} means
print every page up to @var{n}, @samp{@var{n}-} means print every page
beginning with @var{n}.  @code{troff} will exit after printing the last page in
the list.  All the ranges are inclusive on both ends.
@item -r@var{cn}
@itemx -r@var{name}=@var{n}
Set a numerical register @var{c} or @var{name} to the value @var{n};
@var{c} must be a one-letter @var{name}; @var{n} can be any troff
numeric expression.
@item -F@var{dir}
Search @file{@var{dir}} for subdirectories @file{dev@var{name}}
(@var{name} is the name of the device), for the @file{DESC} file and for
font files before the normal directory.
@item -M@var{dir}
Search directory @file{@var{dir}} for macro files before the normal directory.
@end table



@node Environment, Invocation Examples, Options, Invoking groff
@section Environment
@cindex environment variables


Several environment variables modify @code{groff}'s behavior:

@table @code
@cindex @code{GROFF_COMMAND_PREFIX}, environment variable
@item GROFF_COMMAND_PREFIX
If this is set to @var{X}, then @code{groff} will run
@code{@var{X}troff} instead of @code{gtroff}.  This also applies to
@code{tbl}, @code{pic}, @code{eqn}, @code{refer}, and @code{soelim}.  It
does @strong{not} apply to @code{grops}, @code{grodvi}, @code{grotty},
@code{grohtml}, @code{grolj4}, and @code{gxditview}.
@cindex @code{GROFF_TMAC_PATH}, environment variable
@item GROFF_TMAC_PATH
A colon-separated list of directories in which to search for macro
files.
@cindex @code{GROFF_TYPESETTER}, environment variable
@item GROFF_TYPESETTER
The default device.
@cindex @code{GROFF_FONT_PATH}, environment variable
@item GROFF_FONT_PATH
A colon-separated list of directories in which to search for the
@file{dev@var{name}} directories.
@item PATH
The search path for commands executed by groff.
@cindex @code{GROFF_TMPDIR}, environment variable
@item GROFF_TMPDIR
The directory in which temporary files will be created.  If this is not
set and @code{TMPDIR} is set, temporary files will be created in that
directory.  Otherwise temporary files will be created in @code{/tmp}.
The @code{grops} and @code{grefer} commands can create temporary files.
@end table

Note that MS-DOS and MS-Windows ports of @code{groff} use semi-colons,
rather than colons, to separate the directories in the lists described
above.


@node Invocation Examples,  , Environment, Invoking groff
@section Invocation Examples
@cindex invocation examples
@cindex examples of invocation


This section will list several common uses of @code{groff} and the
command line which will accomplish it.

@example
groff file
groff -X -me file
groff -mm -rD1 -z file
groff -tps -me file | lpr -Plw2
... any more?? ...
@end example

@subsection @code{grog}

@pindex grog
@code{grog} reads files, guesses which of the @code{groff}
preprocessors and/or macro packages are required for formatting
them, and prints the @code{groff} command including those options on the
standard output.  The options generated are one of @samp{-e},
@samp{-man}, @samp{-me}, @samp{-mm}, @samp{-ms}, @samp{-p}, @samp{-s},
and @samp{-t}.

A filename of @samp{-} is taken to refer to the standard input.  If no
files are specified the standard input will be read.  Any specified
options will be included in the printed command.  No space is allowed
between options and their arguments.  For example,

@example
`grog -Tdvi paper.ms`
@end example

@noindent
will guess the approriate command to print @file{paper.ms} and then run
it after adding the @samp{-Tdvi} option.


@node Tutorial for Macro Users, Programming Tutorial, Invoking groff, Top
@chapter Tutorial for Macro Users
@cindex tutorial for macro users
@cindex macro tutorial for users
@cindex user's tutorial for macros
@cindex user's macro tutorial

Most users tend to use a macro package to format their papers.  This
means that the whole breadth of @code{groff} is not neccessary for most
people.  This chapter covers the material needed to efficiently use a
macro package.


@menu
* Basics::                      
* Common Features::             
@end menu

@node Basics, Common Features, Tutorial for Macro Users, Tutorial for Macro Users
@section Basics
@cindex basics


This section covers some of the basic concepts you will need to
understand how to use a macro package@footnote{This section is derived from
@cite{Writing Papers with nroff using -me} by Eric P.@: Allman.}.
References are made throughout to more detailed information, if desired.

@code{groff} reads an input file prepared by the user and outputs a
formatted paper suitable for publication or framing.  The input consists
of text, or words to be printed, and embedded commands (@dfn{requests}
and @dfn{escapes}), which tell @code{groff} how to format the printed
copy.  For more detail on this, see @ref{Embedded Commands}.

The word @dfn{argument} is used in this chapter to mean a word or number
which appears on the same line as a request and which modifies the meaning
of that request.  For example, the request

@example
.sp
@end example

@noindent
spaces one line, but

@example
.sp 4
@end example

@noindent
spaces four lines.  The number@w{ }4 is an argument to the @code{sp}
request which says to space four lines instead of one.  Arguments are
separated from the request and from each other by spaces.  More details
on this can be found in @ref{Request Arguments}.

The primary function of @code{groff} is to collect words from input
lines, fill output lines with those words, justify the right-hand margin
by inserting extra spaces in the line, and output the result.  For
example, the input:

@example
Now is the time
for all good men
to come to the aid
of their party.
Four score and seven
years ago,...
@end example

@noindent
will be read, packed onto output lines, and justified to produce:

@quotation
Now is the time for all good men to come to the aid of their party.
Four score and seven years ago,...
@end quotation

@cindex break
@cindex line break
Sometimes you may want to start a new output line even though the line
you are on is not yet full; for example, at the end of a paragraph.  To
do this you can cause a @dfn{break}, which starts a new output line.
Some requests cause a break automatically, as do blank input lines and
input lines beginning with a space.

Not all input lines are text to be formatted.  Some of the input lines
are requests which describe how to format the text.  Requests always
have a period or an apostrophe (@samp{'}) as the first character of the
input line.

The text formatter also does more complex things, such as automatically
numbering pages, skipping over page boundaries to put footnotes in the
correct place, and so forth.

Here are a few hints for preparing text for input to @code{groff}.  First,
keep the input lines short.  Short input lines are easier to edit, and
@code{groff} will pack words onto longer lines for you anyhow.  In
keeping with this, it is helpful to begin a new line after every period,
comma, or phrase, since common corrections are to add or delete
sentences or phrases.  Secondly, do not hyphenate words at the end of
lines -- @code{groff} is smart enough to hyphenate words for you as
needed, but is not smart enough to take hyphens out and join a word back
together.  Also, words such as ``mother-in-law'' should not be broken
over a line, since then you will get a space where not wanted, such as
``mother- in-law''.

@cindex double spacing
@cindex spacing
Groff will double space output text automatically if you use the request
@samp{.ls 2}.  You can revert to single spaced mode by typing @samp{.ls
1}.

A number of requests allow you to change the way the printed copy looks,
sometimes called the @dfn{layout} of the output page.  Most of these
requests adjust the placing of @dfn{white space} (blank lines or
spaces).

The @samp{.bp} request starts a new page.  @xref{Page Control}, for more
details.

The request @samp{.sp @var{N}} leaves @var{N} lines of blank space.
@var{N} can be omitted (meaning skip a single line) or can be of the
form @var{N}i (for @var{N} inches) or @var{N}c (for @var{N}
centimeters).  For example, the input:

@example
.sp 1.5i
My thoughts on the subject
.sp
@end example

@noindent
leaves one and a half inches of space, followed by the line ``My
thoughts on the subject'', followed by a single blank line.

@findex ce
@cindex centering lines
Text lines can be centered by using the @samp{.ce} request.  The line
after @samp{.ce} is centered (horizontally) on the page.  To center more
than one line, use @samp{.ce @var{N}} (where @var{N} is the number of
lines to center), followed by the @var{N} lines.  If you want to center
many lines but don't want to count them, type:

@example
.ce 1000
lines to center
.ce 0
@end example

@noindent
The @samp{.ce 0} request tells @code{groff} to center zero more lines,
in other words, stop centering.

@findex br
@cindex line break
@cindex break
All of these requests cause a break; that is, they always start a new
line.  If you want to start a new line without performing any other
action, use @samp{.br}.

@node Common Features, , Basics, Tutorial for Macro Users
@section Common Features
@cindex common features
@cindex features, common


Groff provides very low level operations for formatting a document.
There are many common routine operations which are done in all documents.
These common operations are written into @dfn{macros} and collected into a
@dfn{macro package}.

All macro packages provide certain common capabilities which fall
into the following categories.

@subsection Paragraphs
@cindex paragraphs

One of the most common and most used capability is starting a
paragraph.  There are a number of different types of paragraphs,
any of which can be initiated with macros supplied by the macro
package.  Normally paragraphs start with a blank line and the first
line indented, like the text in this manual.  There are also block
style paragraphs, which omit the indentation:

@example
Some   men  look   at  constitutions   with  sanctimonious
reverence, and deem them like the ark of the covenant, too
sacred to be touched.
@end example

And there are also indented paragraphs which begin with a tag or label
at the margin and the remaining text indented.

@example
one   This is  the first paragraph.  Notice  how the first
      line of  the resulting  paragraph lines up  with the
      other lines in the paragraph.
longlabel
      This  paragraph   had  a  long   label.   The  first
      character of text on the first line will not line up
      with  the  text  on  second  and  subsequent  lines,
      although they will line up with each other.
@end example

A variation of this is a bulleted list....

@subsection Sections and Chapters

Most macro packages supply some form of section headers.
The simplest kind is simply the heading on a line by itself in bold
type.  Others supply automatically numbered section heading or
different heading styles at different levels.
Some, more sophisticated, macro packages supply macros for starting
chapters and appendicies.

@subsection Headers and Footers

Every macro packages gives you some way to manipulate the headers and
footers (or @dfn{titles}) on each page.  Some packages will allow you
to have different ones on the even and odd pages (for material
printed in a book form).
The titles are called three-part titles, that is, there is a
left-justified part, a centered part, and a right-justified part.
An automatically generated page number may be put in any of these
fields with the @samp{%} character.

@subsection Page Layout

Most macro packages let you specify top and bottom margins and other
details about the appearance of the printed pages.

@subsection Displays
@cindex displays

Displays are sections of text to be set off from the body
of the paper.  Major quotes, tables, and figures are types of
displays, as are all the examples used in this document.

@cindex quotes, major
@cindex major quotes
Major quotes are quotes which are several lines long,
and hence are set in from the rest of the text without
quote marks around them.

@cindex list
A list is an indented, single spaced, unfilled display.  Lists should
be used when the material to be printed
should not be filled and justified like normal text, such
as columns of figures or the examples used in this paper.

@cindex keep
A keep is a display of lines which are kept on a single page if
possible.  An example of where you would use a
keep might be a diagram.  Keeps differ from lists in that
lists may be broken over a page boundary whereas keeps will
not.

@cindex keep, floating
@cindex floating keep
Floating keeps move relative to the text.  Hence, they
are good for things which will be referred to by name, such
as ``See figure 3''.  A floating keep will appear at the bottom of the
current page if it will fit; otherwise, it will
appear at the top of the next page.  Meanwhile, the surrounding text
will `flow' around the keep, thus leaving now blank areas.

@subsection Footnotes and annotations
@cindex footnotes
@cindex annotations

There are a number of requests to save text for later
printing.  Footnotes are printed at the bottom of the current
page.  Delayed text is intended to be a variant form of foot-
note; the text is printed only when explicitly called for,
such as at the end of each chapter.

Delayed text is very similar to a footnote except that
it is printed when called for explicitly.  This allows a
list of references to appear (for example) at the end of
each chapter, as is the convention in some disciplines.

Most macro packages which supply this functionality also supply a
means of automatically numbering either type of annotation.

@subsection Table of Contents

Tables of contents are a type of
delayed text having a tag (usually the page number) attached
to each entry after a row of dots.  The table accumulates
throughought the paper until printed, usually after the paper has
ended.  Many macro packages will provide the abilitly to have several
tables of contents (i.e. one standard one, one for tables, &c.)

@subsection Indexes

While some macro packages will use the term @dfn{index}, none
actually provide that functionality.  The facilities they call
indexes are actually more appropriate for tables of contents.

@subsection Paper formats

Some macro packages provide stock formats for various kinds of
documents.  Many of them provide a common format for the title and
opening pages of a technical paper.  The -mm macros in particular
provide formats for letters and memorandums.

@subsection Multiple Columns

Some macro packages (except -man) provide the ability to have two or
more columns on a page.

@subsection Font and Size changes

The builtin font and size functions are not always intuitive, so all
macro packages provide macros to make these operations simpler.

@subsection Predefined Strings

Most macro packages provide various predefined strings for a variety
of uses, examples are sub- and super-scripts, printable dates, quotes
and various special characters.

@subsection Preprocessor Support

All macro packages provide support for the various preprocessors.

@subsection Configuration and Customization

Some macro packages provide means of customizing many of details of
how the package behaves.  This ranges from setting the default type
size to changing the appearance of section headers.

@ignore
@node -man, -ms, Tutorial for Macro Users, Top
@chapter -man
@cindex @code{-man}



@node -ms, -me, -man, Top
@chapter -ms
@cindex @code{-ms}



@node -me, -mm, -ms, Top
@chapter -me
@cindex @code{-me}



@node -mm, Programming Tutorial, -me, Top
@chapter -mm
@cindex @code{-mm}
@end ignore


@node Programming Tutorial, File formats,  Tutorial for Macro Users, Top
@chapter Programming Tutorial
@cindex programming tutorial
@cindex tutorial for programming

This chapter covers @strong{all} of the facilities of groff.
If you are intending to use a macro package, you probably do not want
to read this chapter.


@menu
* Text::                        
* Input Conventions::           
* Measurements::                
* Expressions::                 
* Identifiers::                 
* Embedded Commands::           
* Registers::                   
* Manipulating Filling and Adjusting::  
* Manipulating Hyphenation::    
* Manipulating Spacing::        
* Tabs and Fields::             
* Character Translations::      
* Line Layout::                 
* Page Layout::                 
* Page Control::                
* Fonts::                       
* Sizes::                       
* Strings::                     
* Conditionals and Loops::      
* Writing Macros::              
* Page Motions::                
* Drawing Functions::           
* Traps::                       
* Diversions::                  
* Environments::                
* I/O::                         
* Postprocessor Access::        
* Miscellany::                  
* Debugging::                   
* Implementation Differences::  
* Summary::                     
@end menu

@node Text, Input Conventions, Programming Tutorial, Programming Tutorial
@section Text
@cindex text

@code{groff} input files contain text with control commands
interspersed throughout.  But, even without control codes,
@code{groff} will still do several things with your text:
filling and adjusting,
adding additional space after sentences,
hyphenating
and
inserting implicit line breaks.


@menu
* Filling and Adjusting::       
* Hyphenation::                 
* Sentences::                   
* Tab Stops::                   
* Implicit Line Breaks::        
@end menu

@node Filling and Adjusting, Hyphenation, Text, Text
@subsection Filling and Adjusting
@cindex filling
@cindex adjusting


When @code{troff} reads in text it collects words from input and fits as many
of them together on one output line as it can.  This is known as
@dfn{filling}.

Once @code{troff} has a @dfn{filled} line it will try to @dfn{adjust} it.
which means it will widen the spacing between words until
the text reaches the right margin (in the default adjustment mode).
Extra spaces between words are preserved, but
spaces at the end of lines are ignored.
Spaces at the front of a line will cause a @dfn{break}.
(Breaks will be explained in @ref{Implicit Line Breaks}.)

@c distribute these through the text
@xref{Manipulating Filling and Adjusting}.

@node Hyphenation, Sentences, Filling and Adjusting, Text
@subsection Hyphenation
@cindex hyphenation


Since the odds of finding a set of words, for every output line,
which will fit nicely on a
line without inserting excessive amounts of space between words
are not great,
troff will hyphenate words so that lines can be justified
without there being too much space between words.
It uses an internal hyphenation algorithm, to indicate which words can
be hyphenated and how to do so.
When a word is hyphenated the first part of the word will be added
to the current filled line being output (with an attached hyphen),
and the other portion will be added to the next line to be filled.

@c distribute these through the text
@xref{Manipulating Hyphenation}.

@node Sentences, Tab Stops, Hyphenation, Text
@subsection Sentences
@cindex sentences


Although it is often debated,
some typesetting rules say there should be different amounts of space
after various puctuation marks.
For example, a period at the end of a sentence
should have twice as much space following it
as would a comma or a period as part of an abbreviation.

@cindex sentence spaces
@cindex spaces between sentences
Troff does this by flagging certain characters (normally
@samp{!},  @samp{?} and @samp{.})
as @dfn{end of sentence} characters.
When @code{troff} encounters one of these characters at the end of a line it
will append two @dfn{sentence spaces} in the formatted output.
(thus, one of the conventions mentioned in @ref{Input Conventions}).

@c also describe how characters like ) are treated here -jjc
@c gotta do some research on this -trent



@node Tab Stops, Implicit Line Breaks, Sentences, Text
@subsection Tab Stops
@cindex tab stops
@cindex stops, tabulator


Groff translates tabs in the input into movements to the next tab
stop.  These tab stops are initially located every half inch across
the page.
Using this you can make simple tables.  However, this can often be
deceptive as the appearance (and width) of your text on a terminal and
the results from groff can vary greatly.

Also, a possible sticking point is that lines beginning with tab
characters will still be filled, again producing unexpected results.
For example, the following input

@example
	1	2	3
		4	5
@end example

@noindent
will produce

@example
	1	2	3		4	5
@end example

@c Tab stops are with respect to the input line.  -jjc
@c did that last section address that?? -trent



@c distribute these through the text
@xref{Tabs and Fields}.

@node Implicit Line Breaks,  , Tab Stops, Text
@subsection Implicit Line Breaks
@cindex implicit line breaks
@cindex implicit breaks of lines
@cindex line, implicit breaks
@cindex break, implicit

An important concept in @code{troff} is the @dfn{break}.  When a @dfn{break}
occurs, @code{troff} will output the partially filled line (unadjusted),
and resume collecting and filling text on the next output line.

@cindex blank line
@cindex empty line
@cindex line, blank
There are several ways to cause a break in @code{troff}.
A blank line will not only cause a break, but it will also cause a
one line vertical space (effectively a blank line) to be output.

A line which begins with a space will cause a break and the space
will be output at the beginning of the next line.
Note that this space isn't adjusted, even in fill mode.

The end of file will also cause a break (otherwise the last line of
your document may vanish!)

Certain @dfn{requests} also cause breaks, implicitly or explicity.
This will be discussed later.

@c distribute these through the text
@xref{Manipulating Filling and Adjusting}.

@node Input Conventions, Measurements, Text, Programming Tutorial
@section Input Conventions
@cindex input conventions
@cindex conventions for input


Since @code{groff} does filling automatically, it is traditional in
@code{groff} not
to try and type things in as nicely formatted paragraphs.  These are
some conventions commonly used when typing @code{groff} text:

@itemize @bullet{}
@item
Break lines after punctuation, particularily at the ends of
sentences, and in other logical places.  Keep separate phrases on
lines by themselves, as entire phrases are often added or deleted
when editing.
@item
Try to keep lines less than 40-60 characters,
to allow space for inserting more text.
@item
Do not try to do any formatting in a WYSIWYG manner (i.e. don't
try and use spaces to get proper indentation).
@end itemize


@node Measurements, Expressions, Input Conventions, Programming Tutorial
@section Measurements
@cindex measurements


@cindex units of measurement
@cindex basic units
@cindex machine units
Troff (like any other programs) requires numeric parameters to
specify various measurements.  Most numeric parameters
(those that specify vertical or horizontal motion or a type
size) may have a measurement unit attached.
These units are specified as a single
character which immediately follows the number or expression.
Each of these units are understood, by @code{troff}, to be a multiple of its
@dfn{basic unit}.  So, whenever a different measurement unit is
specified @code{troff} converts this into its basic units.
This basic unit, represented by a @samp{u} is a
device dependent measurement which is quite small, ranging from
1/75th to 1/72000th of an inch.

Some of the measurement units are completely independent of any of
the current settings (e.g. type size) of @code{groff}.

@table @samp
@item i
@cindex inch
Inches.  An antiquated measurement unit still in use in certain
backwards countries.
@item c
@cindex centimeter
Centimeters.
@item p
@cindex points
Points.  This is a typesetter's measurement used for measure type size.
It is 72 points to an inch.
@item P
@cindex pica
Pica.  Another typesetting measurement.  6 Picas to an inch.
@item s
@item z
@end table

The other measurements understood by @code{troff} are dependent on settings
currently in effect in @code{troff}.  These are very useful for specifying
measurements which should look proper with any size of text.

@table @samp
@item m
@cindex em
Ems.  This unit is equal to the current font size in points.
So called because it is @emph{approximately} the width of the letter
@samp{m} in the current font.
@item n
@cindex en
Ens.  This is half of an em.
@item v
@cindex vertical space
@cindex space, vertical
Vertical space.  This is equivalent to the current line spacing.
@xref{Sizes}, for more information about this.
@item M
100ths of an em.
@end table

@c distribute these through the text
@xref{Fractional Type Sizes}.

@menu
* Default Units::               
@end menu

@node Default Units,  , Measurements, Measurements
@subsection Default Units
@cindex default units
@cindex units, default


Many requests take a default unit.  While this can be helpful at
times, it can cause strange errors in some expressions.
For example, the line  length  request  expects  em's.
Here are several attempts to get 3.5 inches and the results:

@example
3.5i      @result{}   3.5i
7/2       @result{}   0i
7/2i      @result{}   0i
7i/2      @result{}   .1i
7i/2u     @result{}   3.5i
@end example

As you can see, the safest way to specify measurements is to always
attach a scaling indicator.

@node Expressions, Identifiers, Measurements, Programming Tutorial
@section Expressions
@cindex expressions


Troff has most of operators common to other languages:

@itemize @bullet
@item
Arithmetic: +, -, /, *, %
@item
Comparison: <, >, >=, <=, =, ==  (the last two are the same)
@item
Logical: &, :
@item
Unary operators: -, +, ! (if/while only??)
@item
Maximum and minimum: >?, <?
@item
Scaling: (@var{c};@var{e})
Evaluate @var{e} using @var{c} as the default scaling indicator.
If @var{c} is missing, ignore scaling indicators in the
evaluation of @var{e}.
@end itemize

Parentheses may be used as in any other language.
However, in @code{groff} they are necessary to ensure order of evaluation.
Groff has no operator precedence,
expressions are evaluated left to right.
This means that @samp{3+5*4} is evaluated as if it were parenthesized
like @samp{(3+5)*4}, not as @samp{3+(5*4)}, like you may expect.

For many requests which cause a motion on the page, the unary
operators work differently.
The @samp{+} and @samp{-} operators indicate a motion relative to the
current position (down or up, respectively).  The @samp{|} operator
indicates an absolute position on the page or input line. @c (????)
@code{+} and @code{-} are also treated differently by @code{nr}. @c (?)

Due to the way arguments are parsed, spaces are not allowed in
expressions, unless the entire expression is surrounded by parenthesis.

@c distribute these through the text
@xref{Request Arguments}.
@c distribute these through the text
@xref{Conditionals and Loops}.

@node Identifiers, Embedded Commands, Expressions, Programming Tutorial
@section Identifiers
@cindex identifiers

Like any other language, @code{troff} has rules for properly formed
identifiers.
In @code{troff}, an identifier can be made up of most any printable
character.
The only exception is characters which are interpreted by @code{troff}
(backslash, square bracket and @samp{?}).  So, for example, any of the
following are valid:

@example
br
PP
(l
end-list
@@_
@end example

You can test whether an identifier is valid in @code{groff} with the
@code{\A} escape.  It expands to 1 or 0 according whether its argument
(given in quotes) is or is not acceptable as the name of a string,
macro, diversion, number register, environment or font. It will return
0 if no argument is given. This is useful if you want to lookup user
input in some sort of associative table.

Identifiers in @code{groff} can be any length, but, in some contexts,
@code{groff} needs to be told
where identifiers end and text begins (and in different ways
depending on their length):

@itemize @bullet{}
@item
Single character
@item
Two characters:
must be prefixed with @samp{(} in some situations.
@item
Arbitrary length (@code{groff} only):
must be bracketed with @samp{[}, @samp{]} in some situations.
Any length identifier can be put in brackets.
@end itemize

Unlike many other programming languages, undefined identifiers are
silently ignored or expanded to nothing.


@c distribute these through the text
@xref{Interpolating Registers}.
@c distribute these through the text
@xref{Strings}.

@node Embedded Commands, Registers, Identifiers, Programming Tutorial
@section Embedded Commands
@cindex embedded commands
@cindex commands, embedded


With most documents you need more funtionality beyond filling,
adjusting and implicit line breaking.
In order to gain further functionality, @code{groff} allows commands to be
embeded into your text, in two ways.

The first is a @dfn{request} which takes up an entire line, and does
some large scale operation (e.g. break lines, start new pages).

The other is an @dfn{escape} which can be embedded anywhere
in your text, or even as an argument to a request. @c (Not always?)
Escapes generally do more minor operations like sub- and super-
scripts, print a symbol, etc.



@menu
* Requests::                    
* Macros::                      
* Escapes::                     
@end menu

@node Requests, Macros, Embedded Commands, Embedded Commands
@subsection Requests
@cindex requests


@cindex control character
@cindex character, control
A request line begins with a control character,
which is either a single quote (@samp{'}) or a period (@samp{.}).
These can be changed, see @ref{Character Translations}, for details.
After this, there may be optional tabs or spaces followed by an
identifier which is the name of the request.
This may be followed by any number of space separated arguments.

@findex \&@r{, escaping control characters}
If you want to begin a line with a control character without it being
interpreted, precede it with a @code{\&}.  This represents a zero
width space, which means it will not affect you output.

In most cases you will use the period as a control character.
Several requests will cause a break, using the single quote control
character will prevent this.


@menu
* Request Arguments::           
@end menu

@node Request Arguments,  , Requests, Requests
@subsubsection Request Arguments
@cindex request arguments
@cindex arguments to requests


Argument to requests (and macros) are processed much like the shell:
The line is split into arguments according to spaces.
An argument which is intended to contain spaces can either be enclosed
in quotes (single or double), or have the spaces @dfn{escaped} with
backslashes.

Let's look at some examples:

@example
.uh The Mouse Problem
.uh "The Mouse Problem"
.uh The\ Mouse\ Problem
@end example

@noindent
The first line is the @code{.uh} macro being called with 3 arguments,
@samp{The}, @samp{Mouse}, and @samp{Problem}.
The latter two have the same effect or calling the @code{.uh} macro
with a single argument @samp{The Mouse Problem}.

Note, however, that the @code{.ds} request works differently.

@c distribute these through the text
@xref{Strings}.

@node Macros, Escapes, Requests, Embedded Commands
@subsection Macros
@cindex macros


Troff has a @dfn{macro} facility for defining a series of lines which
can be invoked by name.
They are called in the same manner as requests,
and arguments may be passed in the same manner.


@c distribute these through the text
@xref{Writing Macros}.
@c distribute these through the text
@xref{Request Arguments}.

@node Escapes,  , Macros, Embedded Commands
@subsection Escapes
@cindex escapes


Escapes may occur anywhere in the input to @code{groff}.
They begin with a backslash and are followed by a single character
which indicates the function to be performed.

Many escapes have no parameters; those that do, do so in one of two
ways.  For escapes which require an identifier there must be a way for
@code{groff} to tell where the identifier ends and the text begins.
It assumes that the next single character is the identifier, but if
that character is an open parenthesis, it takes the next two
characters as the identifier; and if the next character is an open
bracket, all characters until a close bracket are taken as the
identifier.  Note that in the second case there is no closing
parenthesis.  For example:

@example
\fB
\n(XX
\*[TeX]
@end example

Other escapes may require several arguments and/or some special
format.  In these cases the @dfn{argument} is enclosed in single
quotes (not required??) and the enclosing text is decoded according
to what that escape expects.

@example
\l'1.5i\(bu'
@end example

@findex \\
@findex \e
@findex \E
If you want to have a backslash appear in your output, you can use several
escapes: @code{\\}, @code{\e} or @code{\E}.
These are very similar, and only differ with respect to being used in
macros or diversions (@xref{Copy-in Mode}, and @ref{Diversions}, for
more information).



@c distribute these through the text
@xref{Identifiers}.

@menu
* Comments::                    
@end menu

@node Comments,  , Escapes, Escapes
@subsubsection Comments
@cindex comments


@findex \"
Probably one of the most@footnote{Unfortunately, this is a lie.  But
hopefully future @code{troff} hackers will believe it @code{:-)}.}
common forms of escapes is the comment.
Comments begin with the @code{\"} escape and end at the end of the input
line.

This may sound simple, but it can be tricky to keep the comments from
interfering with the apperarance of your final outupt.

If the escape is to the right of some text or a request, that portion
of the line will be ignored, but the space leading up to it will be
noticed by groff.  This only affects the @code{.ds} request (any
others?).

@cindex tabs before comments
@cindex comments, lining up with tabs
One possibly irritating idiosyncracy is that you mustn't use tabs to
line up your comments.
Tabs are not treated as white space between request and macro
arguments.

If you have a comment on a line by itself, it will be treated as a
blank line, because after eliminating the comment, that is all that
remains.  So, it is common to start the line with @code{.\"} which
will cause the line to be treated as an undefined request.

Another commenting scheme seen sometimes is three consecutive single
quotes (@code{'''}) at the begining of a line.  This works, but @code{groff}
will give a warning about an undefined macro, which is harmless, but
irritating.

@findex \#
To avoid problems with traditional comment styles, @code{groff} has a
new comment mechanism using the
@code{\#} escape.  This escape works the same as @code{\"} except
that the newline is also ignored.

@findex ig
For commenting-out large blocks of text, the @code{ig} request may be
useful; it causes @code{groff} to ignore the entire block until the line
with a lone @code{..}.
@c distribute these through the text
@xref{Strings}.

@node Registers, Manipulating Filling and Adjusting, Embedded Commands, Programming Tutorial
@section Registers
@cindex registers


Registers are @code{groff}'s numeric variables.  @code{groff} has a number of
builtin registers, supplying anything from the date to details of
formatting parameters.

@c distribute these through the text
@xref{Identifiers}.

@menu
* Setting Registers::           
* Interpolating Registers::     
* Auto-increment::              
* Assigning Formats::           
* Builtin Registers::           
@end menu

@node Setting Registers, Interpolating Registers, Registers, Registers
@subsection Setting Registers
@cindex setting registers
@cindex registers, setting


@findex nr
@findex \R
Registers are defined/set via the @code{nr}
request or the @code{\R} escape, for example, the following two lines
are equivalent:

@example
.nr a 1
\R'a 1'
@end example

@findex rr
The @code{rr} request will
remove the register specified by the argument.

@findex rnn
The @code{rnn} request will rename a number register.
The format is @samp{.rnn @var{x} @var{y}}, which will
rename number register  @var{x} to @var{y}.

@findex aln
Aliases can be created for a number register.  The format is
@samp{.aln @var{xx} @var{yy}}, which will create an alias @var{xx} for
number register object named @var{yy}.  The new name and the old name
will be exactly equivalent.  If @var{yy} is undefined, a warning of
type @samp{reg} will be generated, and the request will be ignored.
@xref{Debugging}, for information about warnings.


@node Interpolating Registers, Auto-increment, Setting Registers, Registers
@subsection Interpolating Registers
@cindex interpolating registers
@cindex registers, interpolating


@findex \n
Numeric registers are @dfn{interpolated} via the @code{\n} escape.
@c the following is wrong.  Should I say any more than the above??
@c This means that the value of the number register in expanded in-place
@c on the input line before any other actions, i.e. before requests and
@c escapes are interpreted.

@example
.nr as \na+\na
\n(as
@end example


@node Auto-increment, Assigning Formats, Interpolating Registers, Registers
@subsection Auto-increment
@cindex auto-increment
@cindex increment, automatic

Number registers can also be auto incremented/decremented.  You can
specify the increment/decrement factor with third argument to the
@code{nr} request.  The default value is 0.  For example:

@example
.nr a 0 1
.nr xx 0 5
\n+a, \n+a, \n+a, \n+a, \n+a
.br
\n+(xx, \n+(xx, \n+(xx, \n+(xx, \n+(xx
@end example

@noindent
produces:

@example
1, 2, 3, 4, 5
5, 10, 15, 20, 25
@end example

If you want to change the increment factor without changing the value
of a register, the following can be used:

@example
.nr a \na 10
@end example


@node Assigning Formats, Builtin Registers, Auto-increment, Registers
@subsection Assigning Formats
@cindex assigning formats
@cindex formats, assigning


@findex af
When a register is used in the text of an input file
(as opposed to part of an expression),
it is textually replaced (or interpolated) with a representation of
that number.
This output format can be changed to a variety of formats
(numbers, roman numerals, etc.).
This is done using the @code{af} request.
The first argument to @code{af} is the name of the number register to
be changed,
and the second argument is the output format.
The following output formats are available:

@table @samp
@item 1
This is the default format, decimal numbers:
1, 2, 3, @dots{}
@item 001
Decimal numbers with as many leading zeros as specified.
So, @samp{001} would result in 001, 002, 003, @dots{}
@item I
@cindex roman numerals
@cindex numerals, roman
Upper-case roman numerals:
0, I, II, III, IV, @dots{}
@item i
Lower-case roman numerals:
0, i, ii, iii, iv, @dots{}
@item A
Upper-case letters:
A, B, C, @dots{}, Z, AA, AB, @dots{}
@item a
Lower-case letters:
a, b, c, @dots{}, z, aa, ab, @dots{}
@end table

The following example will produce @samp{10, X, j, 010}.

@example
.nr a 10
.af a 1           \" the default format
\na,
.af a I
\na,
.af a a
\na,
.af a 001
\na
@end example

@findex \g
The @code{\g} escape returns the current format of the specified
register.  For example, @samp{\ga} after the following example would
produce @samp{001}.



@node Builtin Registers,  , Assigning Formats, Registers
@subsection Builtin Registers
@cindex builtin registers
@cindex registers, builtin


The following are some built-in registers, which are not listed
elsewhere in this manual.  Any registers which begin with a @samp{.}
are read-only.  A complete listing of all built-in registers can be
found in @ref{Register Index}.

@table @code
@item .H
@vindex .H
Horizontal resolution in basic units.
@item .V
@vindex .V
Vertical resolution in basic units.
@item dw
@vindex dw
Day of the week (1-7).
@item dy
@vindex dy
Day of the year (1-31).
@item mo
@vindex mo
Current month (1-12).
@item yr
@vindex yr
Last two digits of the current year (see you after year 2000 :-)
@item .c
@vindex .c
@itemx c.
@vindex c.
The current @emph{input} line number.
@item ln
@vindex ln
The current @emph{output} line number.
@item .x
@vindex .x
The  major  version  number.  For example, if the version number is 1.03
then @code{.x} will contain 1.
@item .y
@vindex .y
The minor version number.  For example, if the version number is 1.03
then @code{.y} will contain 03.
@item .g
@vindex .g
Always 1.
Macros should use this to determine whether they are running
under GNU @code{troff}.
@item .A
@vindex .A
If the current output device is @sc{ascii}, this is set to 1,
zero otherwise.
@item .P
@vindex .P
This register indicates whether the current page is actualy being
printed, i.e. if the @samp{-o} option is being used to only print
selected pages.
@xref{Options}, for more information.
@end table

@node Manipulating Filling and Adjusting, Manipulating Hyphenation, Registers, Programming Tutorial
@section Manipulating Filling and Adjusting
@cindex manipulating filling and adjusting
@cindex filling and adjusting, manipulating
@cindex adjusting and filling, manipulating


Several ways of causing @dfn{breaks} were given in
@ref{Implicit Line Breaks}.
The @code{br} request will likewise cause a break.
Several other requests will also cause breaks, implicitly.
They are:
@code{bp},
@code{ce},
@code{fi},
@code{fl},
@code{in},
@code{nf},
@code{sp} and
@code{ti}.

@findex nf
@findex fi
@vindex .u
Initially, groff will fill and ajust text to both margins.
Filling can be disabled via the @code{nf} request
and re-enabled with the @code{fi} request.
These implicitly disable and re-enable adjusting.
Both of these will cause break in text currently being filled.
The number register @code{.u} is equal to 1 in fill mode and 0 in
no-fill mode.

@findex ad
@findex na
@vindex .j
Adjusting can be disabled with the @code{ad} request and re-enabled
with the @code{na} request.
The @code{ad} request takes a single argument to indicate how to
adjust text.
The current adjustment mode is available in the number register
@code{.j}:

@table @samp
@item l
@cindex ragged-right
Adjust text to the left margin.  This produces what is traditionally
called ragged-right text.
@item r
Adjust text to the right margin.
@item c
Center filled text.
@item b
@itemx n
Justify to both margins.  This is @code{groff}'s default.
@end table

With no argument to @code{ad}, @code{troff} will adjust lines the same way
it was the last time it was filling.  For example:

@example
text
.ad r
text
.ad c
text
.na
text
.ad  \" back to centering
text
@end example

@findex \p
The escape @code{\p} will cause a break and cause the remaining text
to be adjusted.

@findex ss
The @code{ss} request allows you to change the minimum size of a
space between filled words.
This request takes its units as one twelfth of the
spacewidth parameter for the current font.  Initially both the word
space size and the sentence space size are 12.

When two arguments are given to the @code{ss} request, the second argument
gives the sentence space size. If the second argument is not given, the
sentence space size will be the same as the word space size.
The sentence space size
is used in two circumstances: if the end of a sentence occurs at the end
of a line in fill mode, then both an inter-word space and a sentence
space will be added; if two spaces follow the end of a sentence in the
middle of a line, then the second space will be a sentence space.  Note
that the behaviour of @sc{Unix} @code{troff} will be exactly that
exhibited by GNU
@code{troff} if a second argument is never given to the @code{ss}
request. In GNU troff, as in @sc{Unix} @code{troff}, you should always
follow a sentence with either a newline or two spaces.

@vindex .ss
@vindex .sss
The number registers @code{.ss} and @code{.sss} hold
the values of the parameters set by the first and second
arguments of the @code{ss} request.

The @code{ce} request will center text.
While the @samp{.ad c} request will also center text, it has the side
effect of filling the text.  The @code{ce} request will not fill the
text it affects.
This request causes a break.

With no arguments, @code{ce} will fill the next line of text.
The single argument @code{ce} takes is a number indicating the
number of lines to be centered.  With no argument centering is
disabled.

A common idiom is to turn on centering for a large number of lines,
and then turn off centering when you are done with the centered text.
This is useful for any request which takes a number of lines as an
argument.

@example
.ce 1000
replace this
with
something
more interesting
@dots{}
.ce 0
@end example

@vindex .ce
The @code{.ce} number register contains the number of lines remaining
to be centered, as set by the @code{ce} request.


@findex rj
@vindex .rj
A similar request is @code{rj} request which will justify unfilled
text to the right margin.  Its arguments are identical to the
@code{ce} request.
The @code{.rj} number register is
the number of lines to be right-justified as set by the @code{rj}
request.



@node Manipulating Hyphenation, Manipulating Spacing, Manipulating Filling and Adjusting, Programming Tutorial
@section Manipulating Hyphenation
@cindex manipulating hyphenation
@cindex hyphenation, manipulating


As discussed in @ref{Hyphenation}, @code{groff} will hyphenate words.
There are a number of ways to modify the how hyphenation is done.

@findex nh
@findex hy
@vindex .hy
This hyphenation can be turned off with the @code{nh} request, and
turned back on with the @code{hy} request.  However, @code{troff}'s
hyphenation facilities are far more flexible than this.  The @code{hy}
request can be used to tell @code{troff} to restrict hypenation to certain
cases.  The request takes a single numeric argument.
The current hyphenation restrictions can be found in the number
register @code{.hy}

@table @samp
@item 1
The default argument, which
indicates to hyphenate without restrictions.
@item 2
Do not hyphenate the last word on a page or column.
@item 4
Do not hyphenate the last two characters of a word.
@item 8
Do not hyphenate the first two characters of a word.
@end table

@findex hlm
@vindex .hlc
@vindex .hlm
The @code{hlm} request will
set the maximum number of consecutive hyphenated lines to the value
given as the first argument.
If this number is
negative, there is no maximum.  The default value is -1.
This value is
associated with the current environment.  Only lines output from an
environment count towards the maximum associated with that environment.
Hyphens resulting from @code{\%} are counted; explicit hyphens are not.
The current setting of this is available in the @code{.hlm} request.
Also the number of immediately preceding consecutive hyphenated lines
are available in the number register @code{.hlc}.

@findex hw
The @code{hw} request allows you to specify how a specific word is
to be hyphenated.  It takes only one argument which is the word with
hyphens at the hyphenation points.  For example:
@samp{.hw in-sa-lub-rious}.
@c In old versions of @code{troff} there was a
@c limited amount of space to store such information, fortunately,
@c with groff, this is no longer a restriction.

@findex \%
@cindex hyphenation character
@cindex character, hyphenation
You can also tell @code{troff} how to hyphenate words on the fly with the
use of the @code{\%} escape, also known as the @dfn{hyphenation
character}.  Preceding a word with this character will prevent it
from being hyphenated, putting it in a word will indicate to @code{troff}
that the word may be hyphenated at that point.  Note that this
mechanism will only affect one word, if you want to change the
hyphenation of a word for the entire document, use the @code{hw}
request.

@findex hc
The @code{hc} request allows you to change the hyphenation character.
The character specified as an argument will then work the same as the
@code{\%} escape, and, thus, no longer appear in the output.  Without
an argument it will return the hyphenation character to @code{\%}.

@findex hpf
To further customize hyphenation the @code{hpf} request will read in
a file of hyphenation patterns.
This file will be searched for in the
same way that @file{tmac.@var{name}} is searched for when the
@samp{-m@var{name}} option is specified.

It should have the same format as the argument to the
\patterns primitive in @TeX{}; the letters appearing in this file are
interpreted as hyphenation codes.
A @samp{%} character in the patterns file
introduces a comment that continues to the end of the line.

@pindex troffrc@r{, specifying hyphenation}
The set of
hyphenation patterns is associated with the current language set by the
@code{hla} request.  The @code{hpf} request is usually invoked by the
@file{troffrc} file.

@findex hcode
The request @samp{.hcode @var{c1} @var{code1} @var{c2} @var{code2}...}
sets the hyphenation code of character @var{c1} to @var{code1}, that of
@var{c2} to @var{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 has its hyphenation code set to itself, and each
upper-case letter has a hyphenation code which is the lower case
version of itself.

@findex hym
@vindex .hym
The @code{hym} request will set the hyphenation margin to the value
given as the first argument: when the current adjustment mode is not
@samp{b}, the line will not be hyphenated if the line is no more than
that amount short.
The default hyphenation margin is 0.  The default scaling
indicator for this request is m.  The hyphenation margin is associated
with the current environment.  The current hyphenation margin is
available in the @code{.hym} register.

@findex hys
@vindex .hys
The @code{hys} request set the hyphenation space to the value given as
the first argument: when the current adjustment mode is @samp{b}, don't
hyphenate the line if the line can be justified by adding no more than
that amount of extra space to each word space.  The default
hyphenation space is 0.  The default scaling indicator for this
request is @samp{m}.  The hyphenation space is associated with the current
environment.  The current hyphenation space is available in the
@code{.hys} register.

@findex shc
The @code{shc} request will set the soft hyphen character to the
argument given as an argument.  If the argument is omitted, the soft
hyphen character will be set to the default @code{\(hy}. The soft
hyphen character is the character which will be 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 will not be broken at that point.  Neither
definitions (specified with the @code{char} request) nor translations
(specified with the @code{tr} request) are considered when finding the soft
hyphen character.

@findex hla
@vindex .hla
The @code{hla} request will set the current hyphenation language to
that given by the first argument.  Hyphenation exceptions specified
with the @code{hw} request and hyphenation patterns specified with the
@code{hpf} request are both associated with the current hyphenation
language.  The @code{hla} request is usually invoked by the
@file{troffrc} file.  The current hyphenation language is available
in the number register @code{.hla}.



@node Manipulating Spacing, Tabs and Fields, Manipulating Hyphenation, Programming Tutorial
@section Manipulating Spacing
@cindex manipulating spacing
@cindex spacing, manipulating


@findex sp
@cindex blank lines
@cindex empty lines
The @code{sp} request will cause @code{troff} to space downwards the
distance specified as the first argument.  With no argument it will
advance 1 line.
A negative argument will cause @code{troff} to move up the page the
specified distance.
If the argument is preceded by a @samp{|} @code{troff} will move that
distance from the top of the page.

@findex ls
@vindex .L
Often you may want your output to be double or triple spaced.
The @code{ls} request will cause @code{troff} to output @var{n}-1 blank
lines after each line of text, where @var{n} is the argument given to
the @code{ls} request.  With no argument @code{troff} will go back to single
spacing.  The number register @code{.L} contains the current line
spacing setting.

@findex \x
@vindex .a
Sometimes, extra vertical spacing is only needed occasionaly,
i.e. to allow space for a tall construct (like an equation).
The @code{\x} escape will do this.
The escape is given a numerical argument (like @samp{\x'3p'}).
If this number is positive extra vertical space will be inserted
below the current line.  A negative number will add space above.
If this escape is used multiple times on the same line, the maximum
values are used.
The @code{.a} number register contains the most recent
extra vertical @strong{emph} line space.

@ignore
@example
... example of inline equation ...
@end example
@end ignore

@findex ns
@findex rs
@cindex no-space mode
@cindex mode, no-space
Spacing (via either @code{sp} or via blank lines) can be disabled
with the @code{ns} request.  This will enable @dfn{no-space mode}.
This mode will end when actual text is output or the @code{rs}
request is encountered.  No-space mode will also prevent requests to
advance to the next page unless they are accompanied by a page number
(see @ref{Page Control}, for more information.)


@node Tabs and Fields, Character Translations, Manipulating Spacing, Programming Tutorial
@section Tabs and Fields
@cindex tabs and fields
@cindex fields and tabs


@findex \t
Tab stops are much like those on a typewriter: a tab character (or the
@code{\t} escape) on input will cause horizontal motion to the next
tab stop.

@findex ta
Tab stops can be changed with the @code{ta} request.
This request takes a series of numbers as arguments which indicate
where each tab stop is to be (overriding any previous settings).
These can be specified absolutely,
i.e. as the distance from the left margin.
For example, the following wil set tab stops every one inch.

@example
.ta 1i 2i 3i 4i 5i 6i
@end example

Tab stops can also be specified relatively (using a leading @samp{+})
which means that the specified tab stop will be set that distance
from the previous tab stop.  For example the following is equivalent
to the previous example.

@example
.ta 1i +1i +1i +1i +1i +1i
@end example

After the specified tab stops repeat values may be set for tabs beyond
the last one specified.  This is most commonly used to specify tabs
set at equal intervals.  The complete syntax for setting tabs is
@samp{.ta @var{n1} @var{n2} @dots{} @var{nn} T @var{r1} @var{r2}
@dots{} @var{rn}}.  This will set tabs at positions @var{n1}, @var{n2},
@dots{}, @var{nn} and then set tabs at @var{nn}+@var{r1},
@var{nn}+@var{r2}, @dots{}, @var{nn}+@var{rn} and then at
@var{nn}+@var{rn}+@var{r1}, @var{nn}+@var{rn}+@var{r2}, @dots{},
@var{nn}+@var{rn}+@var{rn}, and so on.  For example the following is,
yet again, the same as the previous examples.

@example
.ta T 1i
@end example

The material in each tab column may be justified to the right or left
or centered in the column.  This is specified by appending an
@samp{R}, @samp{L} or @samp{C} to the number specifying that tab stop:

@example
.ta 1i 2iC 2iR
@end example

The default justification is @samp{L}.

@vindex .tabs
The number register @code{.tabs} contains
a string representation of the current tab settings suitable for use as
an argument to the @code{ta} request.

@findex tc
Normally @code{troff} will fill the space to the next tab stop with spaces.
In some cases you may wish to change this.  The @code{tc} request
will do this.  With no argument @code{troff} will revert to using spaces.

@subsection Leaders
@cindex leaders

@findex lc
Sometimes you may wish to use the @code{tc} request to fill a tab
stop with a given character, but also, you want to use normal tab
stops on the rest of the line.  For this @code{groff} provides an alternate
tab mechanism, called @dfn{leaders} which will do just that.
They are used exclusively to produce a repeated run of characters to
the next tab stop.

You can declare what character will be repeated with the @code{lc}
request.  If you do not give it an argument, the leaders will act the
same as tabs.

@findex \a
The difference is that a leader is invoked by using the @code{\a}
escape.

@cindex table of contents
@cindex contents, table of
So for a table of contents you may want to have tab stops 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.

@example
.lc .
.ta .5iR 5i +.25i
1.1\tFoo\a\t12
@end example

@subsection Fields
@cindex fields

@findex fc
Fields are a more general way of laying out tabular data.
@code{fc}

@node Character Translations, Line Layout, Tabs and Fields, Programming Tutorial
@section Character Translations
@cindex character translations
@cindex translations of characters


@findex cc
@findex c2
The control character (@samp{.}) and the no-break control character
(@samp{'}) can be changed with the @code{cc} and @code{c2} requests,
respectively.
The single argument is the new character to be used, with no argument
the normal control character is restored.

@findex ec
@findex eo
The @code{eo} request will completely disable the escape mechanism.
The @code{ec} request can be used to change the escape character from
the default @samp{\} to what is specified as an argument.

@findex tr
The @code{tr} request will translate characters.

@findex trnt
@findex \!@r{, and @code{trnt}}
@code{trnt}
This is the same as the @code{tr} request except that the
translations do not
apply to text that is transparently throughput into a diversion with
@code{\!}.  @xref{Diversions}, for more information.
For example,

@example
.tr ab
.di x
\!.tm a
.di
.x
@end example

@noindent
will print @samp{b}; if @code{trnt} is used instead of @code{tr} it
will print @samp{a}.


@node Line Layout, Page Layout, Character Translations, Programming Tutorial
@section Line Layout
@cindex line layout
@cindex layout, line


@cindex dimensions, line
@cindex line dimensions
The following drawing shows the dimensions which @code{troff} uses for
placing a line of output onto the page.  They are labeled with the
requests which manipulate each dimension.

@example
@group
              | -->| in |<--                   |
           -->| po |<-----------ll------------>|
              +----+----+----------------------+----+
              |    :    :                      :    |
              +----+----+----------------------+----+
@end group
@end example

These dimensions are:

@ftable @code
@item po
@vindex .o
@dfn{Page offset}--this is the leftmost postition of text on the final
output.  This can be adjusted with the @code{po} request, and the
current setting can be found in the builtin number register @code{.o}
Note that this request does not cause a break, so changing the page
offset in the middle of text being filled may not do what you expect.
@item in
@vindex .i
@dfn{Indentation}--this is the distance from the left margin where text
will be printed.  This can be adjusted with the @code{in} request, and
the current setting can be found in the builtin number register.
@code{.i}
This request causes a break.

@findex ti
@vindex .in
There is also the request @code{ti} which will cause one output line
to be indented, after which the indentation returns to 0.
This request causes a break.
The number register @code{.in} is the indent that applies to the
current output line.
@item ll
@vindex .l
@vindex .ll
@dfn{Line length}--this is the distance from the left margin to right
margin.  This can be adjusted with the @code{ll} request, and the
current setting can be found in the builtin number register @code{.l}
Note, as the figure implies, line length is not affected by the current
indentation.
The number register @code{.ll} is
the line length that applies to the current output line.
@end ftable

@example
.in +.5i
.ll -.5i
A bunch of really boring text which should
be indented from both margins.
replace me with a better (and more) example!
.in -.5i
.ll +.5i
@end example


@node Page Layout, Page Control, Line Layout, Programming Tutorial
@section Page Layout
@cindex page layout
@cindex layout, page


Troff provides some very primitive operations for controlling page
layout.

@findex pl
@vindex .p
Troff lets you specify the @dfn{page length} via the @code{pl} request.
This is the length of the physical output page.
The current setting can
be found in the builtin number register @code{.p}.  Note that this only
specifies the size of the page, not the top and bottom margins.
Those are not done by @code{groff} directly; see @ref{Traps}, for further
information on how to do this.

@cindex headers
@cindex footers
@cindex titles
Troff provides several operations which help in setting up top and
bottom titles (or headers and footers).

@findex tl
The @code{tl} request will print a @dfn{title line}, which consists
of three parts: a left justified portion, a centered portion and a
right justified portion.  The argument to @code{tl} is specified as
@code{'@var{left}'@var{center}'@var{right}'}
The @samp{%} character is replaced with the current page number.

@findex lt
@vindex .lt
The title line is printed using its own line length, which is
specified with the @code{lt} request.  The current setting of this is
available in the @code{.lt} number register.

@findex pn
The @code{pn} request will change the page number of the @emph{next}
page.  The only argument is the page number.

@vindex %
@vindex .pn
@cindex page number
@cindex current page number
The current page number is stored in the number register @code{%}.
The number register @code{.pn} contains the
number of the next page:
either the value set by a @code{pn} request, or
the number of the current page plus 1.

@findex pc
The @code{pc} request will change the page number character (used by
the @code{tl} request) to a different character.  With no argument,
this mechanism is disabled.


@c distribute these through the text
@xref{Traps}.

@node Page Control, Fonts, Page Layout, Programming Tutorial
@section Page Control
@cindex page control
@cindex control, page


@findex bp
@cindex new page
To stop processing the current page, and move to the next page, you
can invoke the @code{bp} request.  This request will also cause a
break.  This request can also take an argument of what the next page
should be numbered.
The only difference
between @code{bp} and @code{pn} is that @code{pn} does not cause a
break or actually eject a page.

@example
.de newpage
'bp
'sp .5i
.tl 'left top'center top'right top'
'sp .3i
..
@end example

@cindex orphan
@findex ne
Often you may want to make sure that you have a certain amount of
space before a new page occurs.  This is most useful to make sure
that there is not a single @dfn{orphan} line left at the bottom of a
page.  The @code{ne} request will ensure that there is a certain
distance, specified by the first argument, before the next page is
triggered (see @ref{Traps}, for further information).
The default unit for @code{ne} is v's and the default argument
is 1v.

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

@example
.ne 2
.ti +5n
text
@end example

@findex sv
@findex os
The @code{sv} is similar to the @code{ne} request, it reserves the
specified amount of vertical space.  If the desired amount of space
exists before the next trap (bottom page boundary), the space will be
output immediately.  If there is not enough space, it is stored for
later output via the @code{os} request.
The default argument is 1v and the default units are v's.


@node Fonts, Sizes, Page Control, Programming Tutorial
@section Fonts
@cindex fonts


Groff gives you the ability to switch fonts at any point in your
text.  There are two ways to do this, via the @code{ft} request and
the @code{\f} escape.

Fonts are generaly specified as uppercase strings, which are usually
1 to 4 characters representing an abreviation of acronym of the font
name.

The basic set of fonts are R, I, B, and BI.  These are Times Roman,
Italic, Bold, and Bold Italic.  There is also at least one symbol
font which contains various special symbols (greek, mathematics).
These latter fonts cannot be used directly, but should be used via an
escape.


@menu
* Changing Fonts::              
* Font Families::               
* Font Positions::              
* Using Symbols::               
* Artificial Fonts::            
* Ligatures and Kerning::       
@end menu

@node Changing Fonts, Font Families, Fonts, Fonts
@subsection Changing Fonts
@cindex changing fonts
@cindex fonts, changing


@findex ft
You can change fonts with both the @code{ft} request.
With no arguments, it
will switch to the previous font (also known as P).

@example
eggs, bacon,
.ft B
spam
.ft
and sausage.
@end example

@findex \f
The @code{\f} escape is useful for changing fonts in the middle of words.

@example
eggs, bacon, \fBspam\fP and sausage.
@end example

Both of the above examples will produce the same output.

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

@findex \/
The @code{\/} escape
increases the width of the preceding character so that the spacing
between that character and the following character will be correct if
the following character is a roman character.  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 will overlap the top left of the
right parenthesis.
It is a good idea to use this escape sequence
whenever an italic character is immediately followed by a roman
character without any intervening space.

@c producing @i{f}), which is ugly.  Inserting \/ produces f) and avoids this problem.

@findex \,
The @code{\,} escape
modifies the spacing of the following character so that the spacing
between that character and the preceding character will correct if the
preceding character is a roman character.
It is a good idea
to use this escape sequence whenever a roman character is immediately
followed by an italic character without any intervening space.

@c For example, inserting \, between the parenthesis and the f changes (f to (f.

@findex ftr
The @code{ftr} request will translate fonts, it is called as
@samp{.ftr @var{F G}}, which
Translate font @var{F} to @var{G}.
Whenever a font named @var{F} is referred to in @code{\f}
escape sequence,
or in the @code{ft}, @var{ul}, @var{bd}, @var{cs}, @var{tkf},
@var{special}, @var{fspecial}, @var{fp},
or @var{sty} requests, font @var{G} will be used.  If @var{G} is
missing, or equal to @var{F} then font @var{F} will not be translated.


@node Font Families, Font Positions, Changing Fonts, Fonts
@subsection Font Families
@cindex font families
@cindex families, font


Due to the variety of fonts available, @code{groff} has added the concept of
font families.  Each of these families has four styles (R, I, B and BI),

The fonts are specified as the concatenation of the font family and
style.  Specifying a font without the family part will cause @code{groff} to
use that style of the current family.
By default, @code{groff} uses the Times family.

This way, you can just use the basic four fonts and select a
different font family on the command line.

@findex fam
@vindex .fam
You can also switch font families with the @code{fam} request
The current font family is available in the number register
@code{.fam}.
This is a string-valued register.

@example
spam,
.fam H
spam,
.ft B
spam,
.fam T
spam,
.ft AR
baked beans,
.ft R
and spam.
@end example



@node Font Positions, Using Symbols, Font Families, Fonts
@subsection Font Positions
@cindex font positions
@cindex positions, font


For the sake of old phototypesetters and compatability with old
versions of @code{troff}, @code{groff} has the concept of font
@dfn{positions}, on which various fonts are mounted.
The last one or two are reserved for the symbol font(s).

@findex fp
New fonts can be mounted with the @code{fp} request.
These numeric positions can then be referred to with font changing commands.
When @code{groff} starts it is using font number one.

@example
.fp 1 H
.fp 2 HI
.fp 3 HB
wink, wink,
.ft 2
nudge, nudge,
.ft
.ft 3
say no more!
.ft
@end example

@noindent
(note that after these font changes have taken place, the original
font is restored.)

@vindex .f
The current font in use, as a font position.
This can be useful to remember the current font, for later recall.

@example
.nr save-font \n(.f
... lots 'o text ...
.ft \n[save-font]
@end example

@vindex .fp
The number of the next free font position is available in the number
register @code{.fp}.  This is useful when mounting a new font, like so:

@example
.fp \n[.fp] NEATOFONT
@end example

@pindex DESC@r{, and font mounting}
Fonts not listed in the @file{DESC} file are automatically mounted on
the next available font position when they are referenced.
If a font is to be
mountfed explicitly with the @code{fp} request on an unused font position, it
should be mounted on the first unused font position, which can be found
in the @code{.fp} register; although @code{troff} does not enforce this strictly,
it will not allow a font to be mounted at a position whose number is
much greater than that of any currently used position.

The @code{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 @code{troff} after it has been
mounted.  If there is no third argument then the internal name will be
used as the external name.  This feature allows you to use fonts with
long names in compatibility mode.



@node Using Symbols, Artificial Fonts, Font Positions, Fonts
@subsection Using Symbols
@cindex using symbols
@cindex symbols, using


@findex \(
@findex \[
Symbols can be inserted by using a special escape sequence.
This escape is simply the escape character (a backslash) followed by
an identifier.  The symbol identifiers have to be two or more
characters, since single characters conflict with all the other
escapes.  The identifier can be either preceded by a parenthesis if
it is two character, or surrounded by square brackets.
So, the symbol for pi can be produced either by @code{\(*p} or
@code{\[*p]}.

@example
area = \(*p\fIr\fP\u2\d
@end example

@findex \C
The escape @code{\C'@var{xxx}'} will typeset character named
@var{xxx}.  Normally it is more convenient to use @code{\[@var{xxx}]}.
But @code{\C} has the advantage that it is compatible with recent
versions of @code{ditroff} and is available in compatibility mode.

@findex \N
The escape @code{\N'@var{n}'} will typeset the character with code
@var{n} in the current font.  @var{n} can be any integer.  Most devices only
have characters with codes between 0 and 255.  If the current font
does not contain a character with that code, special fonts will not be
searched.  The @code{\N} escape sequence can be conveniently used on
conjunction with the @code{char} request:

@example
.char \[phone] \f(ZD\N'37'
@end example

The code of each character is given in the fourth column in the font
description file after the charset command.  It is possible to include
unnamed characters in the font description file by using a name of
@samp{---}; the @code{\N} escape sequence is the only way to use these.

@findex cflags
Each character has certain properties associated with it.
These properties can be modified with the @code{cflags} request.
The first argument is the the sum of the desired flags and the
remaining arguments are the characters to have those properties.
@table @code
@item 1
the character ends sentences (initially characters @samp{.?!} have this
property);
@item 2
lines can be broken before the character (initially no characters have
this property);
@item 4
lines can be broken after the character (initially characters
@samp{-\(hy\(em} have this property);
@item 8
the character overlaps horizontally (initially characters
@samp{\(ul\(rn\(ru} have this property);
@item 16
the character overlaps vertically (initially character @samp{\(br} has
this property);
@item 32
an end of sentence character followed by any number of characters with
this property will be 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
@samp{"')]*\(dg\(rq} have this property).
@end table

@findex char
@cindex creating new characters
@cindex characters, creating
You can create new characters with the @code{char} request.  It is
called as @samp{.char @var{c} @var{string}}, and defines character @var{c}
to be @var{string}. Every time character @var{c} needs to be printed,
@var{string} will be processed in a temporary environment and the
result will be wrapped up into a single object.  Compatibility mode
will be turned off and the escape character will be set to @samp{\} while
@var{string} is being processed.  Any emboldening, constant spacing or
track kerning will be applied to this object rather than to individual
characters in @var{string}.  A character defined by this request can
be used just like a normal character provided by the output device.
In particular other characters can be translated to it with the
@code{tr} request; it can be made the leader character by the
@code{lc} request; repeated patterns can be drawn with the character
using the @code{\l} and @code{\L} escape sequences;  words containing
the character can be hyphenated correctly, if the @code{hcode} request
is used to give the character a hyphenation code. There is a special
anti-recursion feature: use of character within the character's
definition will be handled like normal characters not defined with
@code{char}.

@findex rchar
@cindex removing characters
@cindex characters, removing
A character definition can be removed with the @code{rchar} request.  Its
arguments are the characters to be removed.  This undoes the effect of
a @code{char} request.

@ignore
@c distribute these through the text
@xref{Special Characters}.
@end ignore

@node Artificial Fonts, Ligatures and Kerning, Using Symbols, Fonts
@subsection Artificial Fonts
@cindex artificial fonts
@cindex fonts, artificial


There are a number of requests for artificially creating fonts.
These are largely vestigal remains from the days when output devices
did not have a wide variety of fonts, and when @code{nroff} and
@code{troff} were separate programs.
These are no longer necessary in GNU Troff.

@findex ul
The @code{ul} request will print subsequent lines in italics on a
device capable of it, or underline the text on an @sc{ascii} output device.
The single argument is the number of lines to be ``underlined,''
with no argument, the next line will be underlined.

@findex cu
The @code{cu} request is similar to @code{ul} ...

@findex uf
The @code{uf} request will set the underline font used by @code{ul}
and @code{cu}.

@findex bd
The @code{bd} request artificially creates a bold font by printing
each character twice, slightly offset.
The first argument specifies the font to embolden, and the second is
the number of basic units, minus one, by which the two characters
will be offset.  If the second argument is missing, emboldening will
be turned off.


@node Ligatures and Kerning,  , Artificial Fonts, Fonts
@subsection Ligatures and Kerning
@cindex ligatures and kerning
@cindex kerning and ligatures


@findex lg
@vindex .lg
@code{lg}
@code{.lg}
The current ligature mode.

@c What is kerning??

If the font description file contains pairwise kerning information,
characters from that font will be kerned.  Kerning between two
characters can be inhibited by placing a @code{\&} between them.

@findex kern
@vindex .kern
@code{kern} enables pairwise kerning if n is non-zero or missing,
otherwise it disables pairwise kerning.
The register @code{.kern} holds the value of
1 if pairwise kerning is enabled, 0 otherwise.

@findex tkf
The request @samp{.tkf @var{f} @var{s1} @var{n1} @var{s2} @var{n2}}
enable track kerning for font @var{f}.  When the current font is
@var{f}, the width of every character will be increased by an amount
between @var{n1} and @var{n2}: when the current point size is less than
or equal to @var{s1}, the width will be increased by @var{n1}; when it
is greater than or equal to @var{s2} the width will be increased by
@var{n2}; when the point size is greater than or equal to @var{s1} and
less than or equal to @var{s2} the increase in width is a linear
function of the point size.


@node Sizes, Strings, Fonts, Programming Tutorial
@section Sizes
@cindex sizes


@cindex baseline
Groff uses two dimensions with each line of text, type size and
vertical spacing.  The type size is the height from the text
@dfn{baseline} to the top of the tallest character (decenders may drop
below this baseline).  Vertical spacing is the amount of space @code{groff}
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 that this, it will spread your text out more
vertically (useful for term papers).  By default, @code{troff} uses 10 point
type on 12 point spacing.

@cindex leading
The difference between type size and vertical spacing is known, by
typesetters, as @dfn{leading}.


@menu
* Changing Type Sizes::         
* Fractional Type Sizes::       
@end menu

@node Changing Type Sizes, Fractional Type Sizes, Sizes, Sizes
@subsection Changing Type Sizes
@cindex changing type sizes
@cindex type sizes, changing


@findex ps
@findex vs
@findex \s
@vindex .s
@vindex .v
Using the @code{ps} request and the @code{\s} escape you can change
the type size.  The @code{vs} request will change the vertical
spacing. The default unit for the @code{ps} and @code{vs} requests are
points.
The number registers @code{.s} and @code{.v} contain the current
type size and vertical spacing.

These requests take parameters in units of points.  You can specify
sizes as an absolute size, or as a relative change from the current
size.  The size 0 means go back to the previous size.  With no
argument it will revert to the previous size.

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

The @code{\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:
@code{\s@var{n}},
@code{\s+@var{n}},
@code{\s-@var{n}},
@code{\s(@var{nn}},
@code{\s+(@var{nn}},
@code{\s-(@var{nn}},
@code{\s[+@var{nnn}]},
@code{\s[-@var{nnn}]},
@code{\s+[@var{nnn}]},
@code{\s-[@var{nnn}]}.

Some devices may only have certain permissible sizes, in which case
@code{groff} will round to the nearest permissible size.

@ignore
@example
... .sz macro example?? ...
@end example
@end ignore

@node Fractional Type Sizes,  , Changing Type Sizes, Sizes
@subsection Fractional Type Sizes
@cindex fractional type sizes
@cindex type sizes, fractional


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

For example, suppose @var{sizescale} is 1000; then a scaled point will be
equivalent to a millipoint; the request @samp{.ps 10.25} is equivalent to
@samp{.ps 10.25z} and so sets the pointsize to 10250 scaled points, which is
equal to 10.25 points.

The number register @code{\n(.s} returns the pointsize in points as
decimal fraction.  There is also a new number register @code{\n[.ps]}
that returns the pointsize in scaled points.

It would make no sense to use the @samp{z} scale indicator in a
numeric expression whose default scale indicator was neither @samp{u}
nor @samp{z}, and so @code{troff} disallows this.  Similarily it would make
no sense to use a scaling indicator other than @samp{z} or @samp{u} in a
numeric expression whose default scale indicator was @samp{z}, and so
@code{troff} disallows this as well.

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

@code{\s'+@var{n}'}
@code{\s'-@var{n}'}
@code{\s+'@var{n}'}
@code{\s-'@var{n}'}:
Set the point size to @var{n} scaled points; @var{n} is a numeric
expression with a default scale indicator of @samp{z}.

@code{\n[.ps]}:
The current pointsize in scaled points.

@code{\n[.psr]}:
The last-requested pointsize in scaled points.

@code{\n[.sr]}:
The last requested pointsize in points as a decimal fraction.  This is a
string-valued register.


@c distribute these through the text
@xref{Font Files}.

@node Strings, Conditionals and Loops, Sizes, Programming Tutorial
@section Strings
@cindex strings


@findex ds
Groff has string variables, which are entirely for user convenience
(i.e. there are no built-in strings).  They are defined via the
@code{ds} request.

@example
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d
@end example

@findex \*
These are interpolated, or expanded in-place, via the @code{\*} escape:

@example
The \*(UX Operating System
@end example

@noindent
will produce:

@example
The UNIXtm Operating System
@end example

If the string named by the @code{\*} does not exist, the escape will
be replaced by nothing.

@cindex comments, with @code{ds}
NOTE:  Unlike other requests the third argument takes up the entire
line including trailing spaces.  This means that comments on a line
with such a request can introduce unwanted space into a string.

@example
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d \" trademark of you-know-who
@end example

Instead you should either put the comment on another line or
have the comment escape adjacent with the end of the string.

@example
.ds UX \s-1UNIX\s0\u\s-3tm\s0\d\"  trademark of you-know-who
@end example

If you need leading space you can start the string with a double
quote.  No trailing quote is needed, in fact any trailing quote is
included in your string.

@cindex cannibalism
@example
.ds sign "           Yours in a white wine sauce,
@end example

@findex as
@cindex appending to strings
@cindex strings, appending
You can also append onto a string with the @code{as} request.
It works the same as the @code{ds} request except that it appends the
second argument onto the string named by the first argument.

@example
.as sign " with shallots, onions and garlic,
@end example

@cindex newlines, in strings
@findex \@key{RET}
Strings are not limited to a sigle line of text.  A string can span
several lines by escaping the newlines with a backslash.  The
resulting string will be stored @emph{without} the newlines.

@example
.ds foo lots and lots \
of text are on these \
next several lines
@end example

@findex rn
@code{rn}

@findex rm
@code{rm}

@findex chop
@code{chop}

@c distribute these through the text
@xref{Identifiers}.
@c distribute these through the text
@xref{Comments}.

@node Conditionals and Loops, Writing Macros, Strings, Programming Tutorial
@section Conditionals and Loops
@cindex conditionals and loops
@cindex loops and conditionals


@findex if@r{, operators to use with it}
@findex while@r{, operators to use with it}
In @code{if} and @code{while} requests, there are several more operators
available:

@table @code
@item e
@itemx o
True if the current page is even or odd numbered (respectively)
@item n
@itemx t
True if the document is being processed by
@code{nroff} (or an @sc{ascii} device) or @code{troff}.
@item '@var{xxx}'@var{yyy}'
True if the string @var{xxx} is equal to the string @var{yyy}.
Other characters can be used in place of the single quotes.
@c (Which?)
The strings are ``formatted'' before being compared. @c (?)
@item r@var{xxx}
True if there is a number register named @var{xxx}.
@item d@var{xxx}
True if there is a string, macro, diversion, or request named @var{xxx}.
@item c@var{ch}
True if there is a character @var{ch} available;  @var{ch} is
either an @sc{ascii} character or a special character @code{\(@var{ch}} or
@code{\[@var{ch}]}; the condition will also be true if @var{ch} has been
defined by the @code{char} request.
@end table


@menu
* if-else::                     
* while::                       
@end menu

@node if-else, while, Conditionals and Loops, Conditionals and Loops
@subsection if-else
@cindex if-else


Troff has if-then-else constructs like other languages, although
the formatting can be painful.

@findex if
The @code{if} request is @code{troff}'s if statement, it is called as
@samp{.if @var{expr} @var{anything}}, where @var{expr} is the
expression to be evaluated,
and @var{anything} (the remainder of the line)
which will be executed if
@var{expr} evaluates to non-zero (true).
@var{anything} will be interpreted as though it was on a line by
itself.
@xref{Expressions}, for more info.

Here are some examples:

@example
.if t .ls 2				\" double spacing in @code{troff}
.if 0 .ab how'd this happen??
@end example

@findex ie
@findex el
An if-then-else is written using two requests @code{ie} and @code{el}
the first request is the if part and the latter is the else part.

@example
.ie
.el
@end example

@findex \@{
@findex \@}
In many cases you will want more than one request to be executed as a
result of any of these requests, this can be done using the \@{ and
\@} escapes.
The following example shows the possible ways to use these escapes.

@example
.ie t \@{\
.    ds lq ``
.    ds rq ''
.\@}
.el \
.\@{\
.    ds lq "
.    ds rq "\@}
.ds qq "
@end example


@c distribute these through the text
@xref{Expressions}.

@node while,  , if-else, Conditionals and Loops
@subsection while
@cindex while


@findex while
Groff provides a looping construct using the @code{while} request,
which is used much like the @code{if} (and related) requests.
The first argument is an expression which will be evaluated.
The @code{while} request will interpret the remainder of the line
until the expression evaluates to 0 or false.

@example
.nr a 0 1
.while (\na<9) \&\n+a,
\&\n+a
@end example

The preceding example produces:

@example
1, 2, 3, 4, 5, 6, 7, 8, 9, 10
@end example

@findex break@r{, in a @code{while} loop}
@findex continue@r{, in a @code{while} loop}
The @code{break} request will
@dfn{break} out of a while loop.
Be sure not to confuse this with the @code{.br} request.
The @code{continue} request will
finish the current iteration of a while loop.

@c distribute these through the text
@xref{Expressions}.

@node Writing Macros, Page Motions, Conditionals and Loops, Programming Tutorial
@section Writing Macros
@cindex writing macros
@cindex macros, writing


@findex de
A macro is a collection of text and embedded commands which can be
invoked multiple times.  Macros are used for defining common operations.
Macros are defined using the @code{de} request.  This request takes
a name for the macro as the first argument.  Subsequent lines are
copied into an internal buffer until the line @code{..} is
encountered.  The optional second argument to @code{de} can change
this ending token.

For example, suppose at the beginning of each paragraph, you want to
cause a break, move down a partial line and indent the first line.
Such a macro could be defined as follows:

@example
.de P
.br
.sp .8v
..
@end example

@findex am
@cindex appending, to a macro
The @code{am} request works similarily to @code{de} except it appends
onto the macro named by the first argument.  So, if we decide we want
our previously @code{P} macro to actually do indented instead of
block paragraphs we can add the necessary code to our existing macro.

@example
.am P
.ti +5n
..
@end example

@findex als
@cindex aliases, macro
@cindex macro aliases
Macros can be aliased with the @code{als} request.

@ignore
@findex rn
@code{rn}

@findex rm
@code{rm}

@findex chop
@code{chop}
@end ignore


@menu
* Copy-in Mode::                
* Parameters::                  
@end menu

@node Copy-in Mode, Parameters, Writing Macros, Writing Macros
@subsection Copy-in Mode
@cindex copy-in mode
@cindex mode, copy-in


@findex \n@r{, when reading test for a macro}
@findex \\@r{, when reading test for a macro}
@findex \*@r{, when reading test for a macro}
@findex \$@r{, when reading test for a macro}
@findex \@key{RET}@r{, when reading test for a macro}
When @code{troff} reads in the test for a macro or diversion it copies the
text (including request lines) into an internal buffer, except for
escapes.  Escapes will be converted into an internal form, except for
@code{\n}, @code{\$}, @code{\*}, @code{\\} and @code{\@key{RET}} which
are evaluated and inserted into the text where the escape was located.
This is known as @dfn{copy-in} mode.

What this means is that you can specify when these escapes are to be
evaluated (copy-in time or time of use) by insulating the escapes
with an extra backslash.

For example, the following will result in the numbers 20 and 10 being
printed.

@example
.nr x 20
.de y
.nr x 10
\&\nx
\&\\nx
..
.y
@end example



@node Parameters,  , Copy-in Mode, Writing Macros
@subsection Parameters
@cindex parameters


@findex \$
@vindex .$
The arguments to a macro can be examined using a variety of escapes.
The number of arguments is available in the @code{.$} number register.
Any individual argument can be retrieved with one of the following
escapes:

The escapes @code{\$@var{n}}, @code{\$(@var{nn}}
and @code{\$[@var{nnn}]}
will result in the @var{n}th, @var{nn}th or @var{nnn}th
argument.  Macros can have a unlimited number of arguments.
Note that due to copy-in mode, you will want to have two backslashes
on these in actual use, since you do not want them interpolated until
the macro is actually invoked.

@findex shift
The request @code{shift} will shift the arguments 1 position, or as
many positions as specified by the first argument.
After executing this request, argument
@var{i} will become argument @var{i}-@var{n}; arguments 1 to @var{n}
will no longer be available.
Shifting by negative amounts is currently undefined.

@findex \$*
@findex \$@@
In some cases you will want to just use all of the arguments at once.
For example if you pass the arguments along to another macro.
The @code{\$*} escape is
the concatenation of all the arguments separated by spaces.
A similar escape is @code{\$@@},
which is
the concatenation of all the arguments with each surrounded
by double quotes, and separated by spaces.

@findex \$0
@findex als@r{, use with @code{\$0}}
The @code{\$0} escape is 
the name by which the current macro was invoked.  The @code{als}
request can make a macro have more than one name.

@example
.de vl
.ie \\n(.$=1 .ds Vl Pre-Release Version
.el          .ds Vl Version \\$3, \\$4.
..
@end example

This would be called as

@example
.vl $Id: groff.texinfo,v 1.5 1999/12/09 09:42:29 wlemb Exp $
@end example


@c distribute these through the text
@xref{Request Arguments}.

@node Page Motions, Drawing Functions, Writing Macros, Programming Tutorial
@section Page Motions
@cindex page motions
@cindex motions, page


@findex sp@r{, as vertical page motion}
Motions up and down the page can be done with the @code{sp} request.
However, this causes a break so that the actual effect is to move to
the left margin and then to the specified location.

@findex mk
@findex rt
The request @code{mk} can be used to mark a location on a page, for
movement to later.  This request takes a register name as an
argument in which to store the current page location, with no
argument it will store the location in an internal register.
The results of this can be used later by the @code{rt} or the
@code{sp} request.  The @code{rt} request will return
@strong{upwards} to the location given in the register name given as
an argument, with no argument it will return to the location marked
with the @code{mk} request

@ignore
@example
... dual column example ...
@end example
@end ignore

There are escapes which will give you much finer control of movements
about the page.

@findex \v
The @code{\v'@var{e}'} will let you do arbitrary vertical motion from
the current location on the page.  The argument @var{e} specifies the
distance to move, positive is downwards and negative upwards.  The
default unit for this escape is vertical spaces, @code{v}'s.  Beware,
however, that @code{troff} will leave text processing to continue wherever
the motion ends, so if you don't want to interfere with text
processing, make sure your motions are balanced.

There are some special case escapes for vertical motion.

@ftable @code
@item \r
move upwards 1v.
@item \u
move upwards .5v.
@item \d
move down .5v.
@end ftable

@findex \h
Horizontal motions can be done via the @code{\h'@var{e}'} escape.
The expression @var{e} indicates how far to move: positive is
rightwards and negative leftwards.

There are a number of special case escapes for horizontal motion:

@cindex inserting horizontal space
@cindex horizontal space
@cindex space, horizontal
@ftable @code
@item \@key{SP}
An unbreakable and unpadable (i.e. not expanded during filling) space.
(Note: this is a backslash followed by a space.)
@item \~
This produces an unbreakable space that stretches like a normal
interword space when a line is adjusted.
@item \|
a 1/6th em space.
@item \^
a 1/12th em space.
@item \0
a space the size of a digit.
@item \&
A zero width space.
@item \)
Like @code{\&} except that it behaves like a character declared with
the @code{cflags} request to be transparent for the purposes of end
of sentence recognition.
@end ftable

@ignore
@example
... tex logo example ...
@end example
@end ignore

@findex \w
@cindex width escape
@cindex escape, width
Often you will want to do horizontal movement based on the width of
some arbitrary text (e.g. given as an argument to a macro).
For that, there is the escape @code{\w'@var{text}'} which will
interpolate to the width of the given @var{text} in basic units.

@ignore
@example
... strlen example ...
@end example
@end ignore

Font changes may occur in @var{text} and not affect current settings.

Also after use, @code{\w} sets several registers:

@table @code
@item st
@vindex st
@itemx sb
@vindex sb
The highest and lowest point, respectively, in @var{text}.
@item rst
@vindex rst
@itemx rsb
@vindex rsb
Like the @code{st} and @code{sb} registers, but takes account of the
heights and depths of characters.
@item ct
@vindex ct
is set according to what kinds of characters occur in @var{text}:
@table @asis
@item 0
all short characters, no decenders or tall characters.
@item 1
decender
@item 2
tall character
@item 3
both a decender and a tall character
@end table
@item ssc
@vindex ssc
The amount of horizontal space (possibly negative) that should be
added to the last character before a subscript.
@item skw
@vindex skw
How far to right of the center of the last character in the @code{\w}
argument, the center of an accent from a roman font should  be
placed over that character.
@end table

@findex \k
@vindex .k
@code{\k}
@code{.k}

@node Drawing Functions, Traps, Page Motions, Programming Tutorial
@section Drawing Functions
@cindex drawing functions
@cindex functions for drawing


Groff provides a number of ways to draw lines, and other figures on
the page.  Used in combination with the page motion commands
(see @ref{Page Motions}, for more info) you can draw a wide variety of
figures.  However, for complex drawings these operations can be quite
cumbersome, and it may be wise to use the pic preprocessor.
@ignore
@xref{gpic}, for more information.
@end ignore

All drawing is done via escapes.

@findex \l
@cindex drawing horizontal lines
@cindex line, horizontal
@cindex horizontal lines, drawing
The @code{\l} will draw a line rightwards from the current location.
The full syntax for this escape is @samp{\l'@var{l}@var{c}'}, where
@var{l} is the length of the line to be drawn, starting at the
current location, positive numbers will draw to the right, and
negative will draw towards the left.  This can also be specified
absolutely (i.e. with a leading |) which will draw back to the
begining of the line.

The optional second parameter @var{c} is a character to draw the line
with.  If this second argument is not specified, @code{troff} will use the
underscore character.

If you need to separate the two arguments (to prevent @code{troff} from
interpreting a drawing character as a scaling indicator), you can
separate them with @code{\&}.

And now, for a useful example:

@example
.de box
\(br\\$*\(br\l'|0\(rn'\l'|0\(ul'
..
@end example

Note that this works by outputing a box rule (a vertical line), then
the text given as an argument and then another box rule.
Then the line drawing escapes both draw from the current location to
the beginning of the @emph{input} line.

@findex \L
@cindex drawing vertical lines
@cindex line, vertical
@cindex vertical lines, drawing
Vertical lines are drawn using the @code{\L} escape.  Its parameters
are specified the same as the @code{\l} escape.  If the length is
positive, the movement will be downwards, and upwards for negative.
The default character is the box rule character.
As with the vertical motion escapes, text processing will blindly
continue where the line ends.

@ignore
@example
...box macro...
@end example
@end ignore

@findex \D
More flexible drawing functions are available via the @code{\D}
escape.  While the previous escapes will work on an @sc{ascii} device,
these escapes will not.

@table @code
@item \D'l @var{x} @var{y}'
Draw a line from the current location to the relative point specified
by @var{x}, @var{y}.

@ignore
@example
...revised box macro...
@end example
@end ignore

@item \D'c @var{d}'
@cindex drawing a circle
@cindex circle drawing
Draw a circle with a diameter of @var{d} with the leftmost point at
the current position.
@item \D'C @var{d}'
Draw a solid circle with the same parameters as an outlined circle.
@item \D'e @var{dx} @var{dy}'
@cindex ellipse drawing
@cindex drawing an ellipse
Draw an ellipse with a horizontal diameter of @var{dx} and a vertical
diameter of @var{dy} with the leftmost point at the current position.
@item \D'E @var{dx} @var{dy}'
Draw a solid elipse with the same parameters as an outlined elipse.
@item \D'a @var{dx1} @var{dy1} @var{dx2} @var{dy2}'
@cindex arc drawing
@cindex drawing an arc
Draw an arc clockwise from the current location through the two
specified locations.
@item \D'~ @var{dx1} @var{dy1} @var{dx2} @var{dy2} ...'
@cindex spline drawing
@cindex drawing a spline
Draw a spline from the current location to
@var{dx1}, @var{dy1} and then to @var{dx2}, @var{dy2}, and so on.
@item \D'f @var{n}'
@cindex filling, shades of gray
@cindex shades for filling
Set the shade of gray to be used for filling solid objects to @var{n};
@var{n} must be an integer between 0 and 1000, where 0 corresponds
solid white and 1000 to solid black, and values in between correspond
to intermediate shades of gray.  This applies only to solid circles,
solid ellipses and solid polygons.  By default, a level of 1000 will
be used.
@item  \D'p @var{dx1} @var{dy1} @var{dx2} @var{dy2} ...'
@cindex polygon drawing
@cindex drawing a polygon
Draw a polygon from the current location to @var{dx1}, @var{dy1}
and then to @var{dx2}, @var{dy2} and so on.  When the specified data
points are exhausted, a line is drawn back to the starting point.

@ignore
@example
... box example (yes, again)...
@end example
@end ignore

@itemx \D'P @var{dx1} @var{dy1} @var{dx2} @var{dy2} ...'
Draw a solid polygon with the same parameters as an outlined polygon.

@ignore
@example
... shaded box example ...
@end example
@end ignore

@item \D't @var{n}'
Set the current line thickness to @var{n} machine units.
A value of zero selects the smallest available line thickness.

@end table

@ignore
@c what is this for???
Current position 
@end ignore

@findex \b
@cindex pile, character
@cindex character pile
The @code{\b} escape will @dfn{pile} a sequence of characters
vertically, and center it vertically on the current line.
This can be used to build large brackets and braces.

@example
\b'\(lt\(bv\(lk\(bv\(lb'
@end example




@node Traps, Diversions, Drawing Functions, Programming Tutorial
@section Traps
@cindex traps


Traps are locations, which, when reached, will call a specified macro.
These traps can occur at a given location on the page, at a given
location in the current diversion, after a certain number of input
lines or at the end of input.

Any of these traps can be changed after they have been set with the
@code{ch} request.  The first argument is the name of the trap or
macro, and the second is the new value for that trap.  @xref{Page
Location Traps}.


@menu
* Page Location Traps::         
* Diversion Traps::             
* Input Line Traps::            
* End-of-input Traps::          
@end menu

@node Page Location Traps, Diversion Traps, Traps, Traps
@subsection Page Location Traps
@cindex page location traps
@cindex traps, page location


Page location traps are frequently used for page headers and
footers.  The following is a simple example of this.

@example
.de hd                          \" Page header
'sp .5i
.tl 'Title''date'
'sp .3i
..
.de fo                          \" Page footer
'sp 1v
.tl ''%''
'bp
..
.wh 0   hd                      \" top of the page
.wh -1i fo                      \" one inch from bottom
@end example

@vindex .t
The number register @code{.t} is the distance to the next trap.

@findex ch
The location of a trap can be changed later on with the @code{ch}
request.
The first argument is the name of the macro to be invoked at the trap
and the second argument is the new location for the trap.
This is useful when you are building up footnotes in a diversion, and
you need to allow more space at the bottom of the page for them.

@ignore
@example
... (simplified) footnote example ...
@end example
@end ignore

@findex vpt
@findex wh
@vindex .vpt
The @code{vpt} request will enable vertical position traps if the argment is
non-zero, disable them otherwise.  Vertical position traps are traps
set by the @code{wh} or @code{dt} requests.  Traps set by the
@code{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.  The current setting of
this is available in the number register @code{.vpt}.

@vindex .trunc
@findex ne@r{, and the @code{.trunc} register}
The number register @code{.trunc} contains
the amount of vertical space truncated by the most recently
sprung vertical position trap, or, if the trap was sprung by a
@code{ne} request, minus the amount of vertical motion produced by
the @code{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.

@vindex .ne
The number register @code{.ne} contains
the amount of space that was needed in the last @code{ne} request that caused
a trap to be sprung.  Useful in conjunction with the @code{.trunc}
register.  @xref{Page Control}, for more information.



@node Diversion Traps, Input Line Traps, Page Location Traps, Traps
@subsection Diversion Traps
@cindex diversion traps
@cindex traps, diversion


@findex dt
@vindex .t@r{, and diversions}
Traps can also be set @emph{within} a diversion using the @code{dt}
request.  Like @code{wh} the first argument is the location of the
trap and the second argument is the name of the macro to be invoked.
The number register @code{.t} will still work within diversions.
@xref{Diversions}, for more information.

@node Input Line Traps, End-of-input Traps, Diversion Traps, Traps
@subsection Input Line Traps
@cindex input line traps
@cindex traps, input line


@findex it
The @code{it} request will set an input line trap.  The format for
calling this is @samp{.it @var{n} @var{name}}, where @var{n} is the
number of lines of input which may be read before @dfn{springing} the
trap, @var{name} is the macro to be invoked.  Request lines are not
counted as input lines.

For example, one possible use is to have a macro which will print the
next @var{n} lines in a bold font.

@example
.de B
.it B-end \\$1
.ft B
..
.de B-end
.ft R
..
@end example

@node End-of-input Traps,  , Input Line Traps, Traps
@subsection End-of-input Traps
@cindex end-of-input traps
@cindex traps, end-of-input


@findex em
The @code{em} request will set a trap at the end of input.
The macro specified as an arguement will be executed after the last
line of the input file has been processed.

For example, if your document had to have a section at the bottom of
the last page for someone to approve you document, you could set it
up with @code{em}.

@example
.de approval
.ne 5v
.sp |(\\n(.t-6v)
.in +4i
.lc _
.br
Approved:\t\a
.sp
Date:\t\t\a
..
.em approval
@end example


@node Diversions, Environments, Traps, Programming Tutorial
@section Diversions
@cindex diversions


In Troff you can divert text into a named storage area, due to the
similarity to defining macros it is sometimes said to be stored in a
macro.  This is used for saving text for output at a later time,
which is useful for keeping blocks of text on the same page,
footnotes, tables of contents and indexes.

@findex di
@findex da
Diversion is initiated by the @code{di} request, like the @code{de}
request it takes an argument of a macro name to divert subsequent
text to into.  The @code{da} macro will append to an existing diversion.

@ignore
@example
... end-note example ...
@end example
@end ignore

@vindex .z
@vindex .d
@vindex nl
@vindex .h
Diversions may be nested.
The number register @code{.z} contains the name of the current diversion.
The number register @code{.d} contains the current vertical place in
the diversion.  If not in a diversion it is the same as the register
@code{nl}.
@code{.h}

@vindex dn
@vindex dl
After completing a diversion, the builtin number registers @code{dn}
and @code{dl} contain the vertical and horizontal size of the diversion.

@example
.\" Center text both horizontally & vertically
.de (c
.br
.nf
.di @@c
..
.de )c
.br
.di
.nr @@s (((\\n(.tu-\\n(dnu)/2u)-1v)
.sp \\n(@@su
.ce 1000
.nf
.@c
.br
.ce 0
.sp \\n(@@su
.br
.fi
.rr @@s
..
@end example

@findex \!
Requests, macros and escapes are interpreted when read into a
diversion.
There are two ways to prevent this, either way will take the given
text and @dfn{transparently} embed it into the diversion.
The first method is to prefix the line with @code{\!}.  This will
cause the entire line to be transparently inserted into the diversion.
This is useful for macros you do not want invoked until the diverted
text is actually output.

@c anything  is  read  in  copy  mode. (what about \! ??)

@findex \?
The other way is to surround the text by the @code{\?} escape, i.e.
@samp{\?@var{anything}\?}.
@var{anything} may not  contain
newlines; use @code{\!} if you want to embed newlines in a diversion.  The
escape sequence @code{\?} is also recognised in copy mode and turned into a
single internal code; it is this code that terminates anything.  Thus
the followin example will print 4.

@example
.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
@end example

@findex rn@r{, and diversions}
@code{rn}

@findex rm@r{, and diversions}
@code{rm}

@findex als@r{, and diversions}
@code{als}

@findex chop@r{, and diversions}
@code{chop}

@findex asciify
The @code{asciify}
request only exists in order to make it possible to make certain
gross hacks work with GNU @code{troff}.  It @dfn{unformats} the diversion
specified as an argument in
such a way that @sc{ascii} characters that were formatted and diverted
will be treated like ordinary input characters when the diversion is
reread.  For example, the following will set register @code{n} to 1.

@example
.tr  @@.
.di  x
@@nr\  n\  1
.br
.di
.tr  @@@@
.asciify  x
.x
@end example


@c distribute these through the text
@xref{Copy-in Mode}.

@node Environments, I/O, Diversions, Programming Tutorial
@section Environments
@cindex environments


Often you will need to print some text in a certain format regardless
of what may be in effect at the time, for example, in a trap invoked
macro to print headers and footers.
To solve this, @code{groff} has @dfn{environments} in which text is processed.
An environment contains most of the parameters that control
text processing.  You can switch amongst these environments; by
default, @code{groff} processes text in environment 0.
The following is the information kept in an environment.

@itemize @bullet{}
@item
type size
@item
font (family and style)
@item
page parameters
@item
fill/adjust mode
@item
tab stops
@item
partially collected lines
@end itemize

These environments may be given arbitrary names
(see @ref{Identifiers}, for more info).
Old versions of @code{troff} only had environments named 0, 1 and 2.

@findex ev
@vindex .ev
The @code{ev} request will switch among these environments.
The single argument is the name of the environment to switch to, with
no argument groff will switch back to the previous enviroment.
There is no limit on the number of named environments;
they will be created the first time that they are referenced.
The @code{.ev} number register contains
the name or number of the current environment.  This is a string-valued
register.

@example
... page break macro, revised ...
@end example

@example
.ev footnote-env
.fam N
.ps 6
.vs 8
.ll -.5i
.ev
...
.ev footnote-env
\(dg Note the large, friendly letters.
.ev
@end example




@node I/O, Postprocessor Access, Environments, Programming Tutorial
@section I/O
@cindex i/o


@findex so
@cindex including a file
@cindex file inclusion
The @code{so} request will read in the file given as an argument and
include it in place of the @code{so} request.  This is quite useful
for large documents, i.e. keeping each chapter in a separate file.
@ignore
@xref{gsoelim}, for more information.
@end ignore

@findex mso
The @code{mso} request is
the same as the @code{so} request except that file is searched for in
the same way that @file{tmac.@var{name}} is searched for when the
@samp{-m@var{name}} option is specified.

@findex cf
@findex trf
The @code{cf} and @code{trf} requests are to include a file.
It will transparently output the contents of file filename.  Each
line is output
as it would be were it preceded by @code{\!}; however, the lines are not
subject to copy-mode interpretation.  If the file does not end with a
newline, then a newline will be added.  For example, you can define a
macro @code{x} containing the contents of file @file{f}, using

@example
.di x
.trf f
.di
@end example

The request @samp{.cf @var{filename}},
when  used  in  a  diversion, will embed in the diversion an object
which, when reread, will cause the contents of @var{filename} to be
transparently copied through to the output.  In @sc{Unix} @code{troff}, the contents
of @var{filename} is immediately copied through to the output regardless of
whether there is a current diversion; this behaviour is so anomalous
that it must be considered a bug.


With @code{trf}, unlike @code{cf}, the file cannot contain characters
such as NUL that are not valid @code{troff} input characters.

@findex nx
The @code{nx} request will force @code{groff} to continue processing of the
file specified as an argument.

@findex rd
The @code{rd} request will read from standard input, and include what
is read as though it were part of the input file.  Text is read until
a blank line is encountered.

@cindex form letters
@cindex letters, form
Using these two requests you can set up form letters.
The form letter template is constructed like this:

@example
.ce
\*(td
.sp 2
.nf
.rd
.sp
.rd
.fi
Body of letter.
.bp
.nx repeat.let
@end example

@findex ex
When this is run, the following file should be redirected in.
Note that requests included in this file are executed as though they
were part of the form letter.  The last block of input is the
@code{ex} requests which tells groff to stop processing.  If this was
not there, groff would not know when to stop.

@cindex Beagle Brothers
@example
Trent A. Fisher
708 NW 19th Av., #202
Portland, OR  97209

Dear Trent,

Len Adollar
4315 Sierra Vista
San Diego, CA  92103

Dear Mr. Adollar,

.ex
@end example

@findex pi
@code{pi}

@findex sy
The @code{sy} request will allow arbitrary system commands to be
executed from within a groff document.  The output is not saved
anyplace, so it is up to you to do so.

For example, the following example will introduce the current time
into your document:

@cindex time
@pindex perl
@example
.sy perl -e 'printf ".nr H %d\\n.nr M %d\\n.nr S %d\\n",\
	     (localtime(time))[2,1,0]' > /tmp/x\n[$$]
.so /tmp/x\n[$$]
.sy rm /tmp/x\n[$$]
\nH:\nM:\nS
@end example

Note that this works by having the perl script (run by @code{sy})
print out the @code{nr} requests which will set the number registers
@samp{H}, @samp{M} and @samp{S}, and then reads those commands in
with the @code{so} request.

@vindex systat
The @code{systat} number register contains
The return value of the @code{system()} function executed by the last
@code{sy} request.

@findex open
The @code{open} request will open
a file (specified as the second argument) for writing and associate
the stream (specified as the first argument) with it.

@findex opena
The @code{opena} is
like open, but if filename exists, append to it instead of truncating
it.

@findex write
@cindex copy-in mode, and @code{write} requests
@cindex mode, copy-in, and @code{write} requests
The @code{write} request will write to the file associated with the
stream specified by the first argument.  The stream must previously
have been the subject of an open request.  The remainder of the line
in interpreted as the @code{ds} request reads its second argument: a
leading @code{"} will be stripped, and it will be read in copy-in mode.

@findex close
The @code{close} request will
close the stream specified by the first argument; stream will no
longer be an acceptable argument to the @code{write} request.

@ignore
@example
... example of open write &c...
@end example
@end ignore

@findex \V
The @code{\V} escape will
interpolate the contents of the specified environment variable, as returned
by @code{getenv(3)}.
The argument to @code{\V} is specified as an identifier, i.e.
@samp{\V@var{x}}, @samp{\V(@var{xx}} or @samp{\V[@var{xxx}]}.
@code{\V} is interpreted in copy-in mode.


@node Postprocessor Access, Miscellany, I/O, Programming Tutorial
@section Postprocessor Access
@cindex postprocessor access
@cindex access of postprocessor


There are two escapes which will allow you to give information
directly to the postprocessor.  This is particularly useful for
embedding PostScript into your final document.

@findex \X
The @code{\X} escape will embed its argument into the gtroff output
preceded with @samp{x X}.

@findex \Y
The @code{\Y} escape is called with an identifier (i.e.
@code{\Y@var{x}},
@code{\Y(@var{xx}} or
@code{\Y[@var{xxx}]}).
This is approximately equivalent to @samp{\X'\*[@var{xxx}]'}.
However the contents
of the string or macro @var{xxx} are not interpreted; also it is
permitted for
@var{xxx} to have been defined as a macro and thus contain newlines
(it is not permitted for the argument to @code{\X} to contain newlines).
The inclusion of
newlines requires an extetension to the @sc{Unix} @code{troff} output format, and will
confuse drivers that do not know about this extension.


@c distribute these through the text
@ignore
@xref{Devices}.
@end ignore

@node Miscellany, Debugging, Postprocessor Access, Programming Tutorial
@section Miscellany
@cindex miscellany


This section contains parts of @code{troff} which cannot (yet) be
categorized elsewhere in this manual.

@findex nm
Line numbers can be printed in the left margin
using the @code{nm} request.
The first argument is the line number of the @emph{next} output line,
this defaults to 1.
The second argument indicates on which lines numbers will be printed,
i.e. 5 means put line numbers on every 5 lines, this defaults to 1.
The third argument is the space to be left between the number and
your text, this defaults to 1.
The fourth argument is the indentation of the line numbers.
Without arguments, line numbers are turned off.

@findex nn
The @code{nn} request will temporarily turn off line numbering.
The first argument is the number of lines not to be numbered,
this defaults to 1. (does this disable incrementing or display?)

@ignore
@example
... line numbering example ...
@end example
@end ignore

@findex mc
margin characters can be automatically printed to the right of your
text with the @code{mc} request.
The first argument is the character to be printed and the second
argument is the distance away from your text.
With no arguments the margin characters are turned off.
If this occurs before a break, no margin character will be printed.

This is quite useful for indicating text that has changed, and, in
fact, there are programs available for doing this (they are called
@code{nrchbar} and @code{changebar} and can be found in any
@samp{comp.sources.unix} archive.

@ignore
@example
... margin char example ...
@end example
@end ignore

@findex lf
@pindex soelim
The @code{lf} primary reason for existence is to make debugging
documents which are split into many files, which are then put
together with @code{soelim} and other preprocessors.
The first argument is the name of the file and the second argument is
the input line number in that file.
This way @code{troff} can produce error messages which are intelligible to
the user.

@ignore
@example
... example of soelim'ed doc ...
@end example
@end ignore

@node Debugging, Implementation Differences, Miscellany, Programming Tutorial
@section Debugging
@cindex debugging


Troff is not easy to debug, but there are some useful features and
strategies for debugging.

@itemize @bullet{}
@item
@findex tm
The @code{tm} request will send output to the standard error stream,
this is very useful for printing debugging output.
@item
When doing something involved it is useful to leave the debugging
statements in the code and have them turned on by a command line
flag.

@example
.if \n(DB .tm debugging output
@end example

Then you can activate these statements with:

@example
groff -rDB=1 file
@end example

@item
@findex ab
The @code{ab} request is similar to the @code{tm} request,
except that it will cause groff to stop processing.
With no argument it will print @samp{User Abort}.
@item
@findex ex@r{, use in debugging}
The @code{ex} request will also cause @code{groff} to stop processing.
@item
If you know you are going to get many errors and no useful output,
you can tell @code{groff} to suppress formatted output with the @samp{-z}
flag.
@item
@findex pm
The @code{pm} request will dump out the entire symbol table.
@item
@findex pnr
The @code{pnr} request will print the names and contents of all
currently defined number registers on stderr.
@item
@findex ptr
The @code{ptr} request will
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.
@item
@findex fl
The @code{fl} request instructs @code{groff} to flush its output immediately.
The intention is that this be used when using @code{troff} interactively.
There is little other use for it.
@item
@findex backtrace
The @code{backtrace} request will
print a backtrace of the input stack on @code{stderr}.
@item
Groff has command line options for printing out more warnings
(@samp{-w}) and for printing backtraces (@samp{-b}) when a warning or
an error occurs.  The most verbose level of warnings is @samp{-ww}.
@item
@findex warn
@vindex .warn
The @code{warn} request controls the level of warnings checked for.
The one argument is the sum of the numbers associated with each
warning that is to be enabled; all other warnings will be disabled.
The number associated with each warning is listed below.
For example, @code{.warn 0} will disable all warnings, and
@code{.warn 1} will disable
all warnings except that about missing characters.  If an argument
is not given, all warnings will be enabled.
The number register @code{.warn} contains the current warning level.
@end itemize

@subsection Warnings
@cindex warnings

The warnings that can be given by @code{troff} are divided into the
following categories.  The name associated with each warning is used
by the @samp{-w} and @samp{-W} options; the number is used by the
@code{warn} request, and by the @code{.warn} register.

@table @samp
@item  char
@itemx 1
Non-existent characters.  This is enabled by default.
@item  number
@itemx 2
Invalid numeric expressions.  This is enabled by default.
@item  break
@itemx 4
In fill mode, lines which could not be broken so that
their length was less than the line length.  This is
enabled by default.
@item  delim
@itemx 8
Missing or mismatched closing delimiters.
@item  el
@itemx 16
Use of the @code{el} request with no matching @code{ie} request.
@xref{if-else}, for more information.
@item  scale
@itemx 32
Meaningless scaling indicators.
@item  range
@itemx 64
Out of range arguments.
@item  syntax
@itemx 128
Dubious syntax in numeric expressions.
@item  di
@itemx 256
@findex di@r{, debugging}
@findex da@r{, debugging}
Use of @code{di} or @code{da} without an argument when there is no
current diversion.
@item  mac
@itemx 512
Use of undefined strings, macros and diversions.
When an undefined string, macro or diversion is used,
that string is automatically defined as empty.  So,
in most cases, at most one warning will be given for
each name.
@item  reg
@itemx 1024
Use of undefined number registers.  When an undefined
number register is used, that register is
automatically defined to have a value of 0.  a
definition is automatically made with a value of 0.
So, in most cases, at most one warning will be given
for use of a particular name.
@item  tab
@itemx 2048
Use of a tab character where a number was expected.
@item  right-brace
@itemx 4096
@findex \@}@r{, debugging}
Use of @code{\@}} where a number was expected.
@item  missing
@itemx 8192
Requests that are missing non-optional arguments.
@item  input
@itemx 16384
Illegal input characters.
@item  escape
@itemx 32768
Unrecognized escape sequences.  When an unrecognized
escape sequence is encountered, the escape character
is ignored.
@item  space
@itemx 65536
Missing space between a request or macro and its
argument.  This warning will be given when  an
undefined name longer than two characters is
encountered, and the first two characters of the name
make a defined name.  The request or macro will not
be invoked. When this warning is given, no macro is
automatically defined.  This is enabled by default.
This warning will never occur in compatibility mode.
@item  font
@itemx 131072
Non-existent fonts. This is enabled by default.
@item all
All warnings except @samp{di}, @samp{mac} and @samp{reg}. It is
intended that this covers
all warnings that are useful with traditional macro packages.
@item w
All warnings.
@end table


@node Implementation Differences, Summary, Debugging, Programming Tutorial
@section Implementation Differences
@cindex implementation differences
@cindex differences in implementation
@cindex incompatibilites with Unix @code{troff}


GNU @code{troff} has a number of features which cause incompatibilites with
documents written with old versions of @code{troff}.

Long names cause some incompatibilities.  @sc{Unix} @code{troff} will interpret

@example
.dsabcd
@end example

@findex \*@r{, incompatibilities with Unix @code{troff}}
@findex \n@r{, incompatibilities with Unix @code{troff}}
@findex cp
@vindex .C
@noindent
as defining a string @samp{ab} with contents @samp{cd}.
Normally, GNU @code{troff} will interpret this as a call of a macro named
@code{dsabcd}.  Also @sc{Unix} @code{troff} will interpret @code{\*[} or
@code{\n[} as references to a string or number register called
@samp{[}.  In GNU @code{troff}, however, this will normally be interpreted as the
start of a long name.  In compatibility mode GNU @code{troff} will interpret
these things in the traditional way.  In compatibility mode, however,
long names are not recognised.  Compatibility mode can be turned on with
the @samp{-C} command line option, and turned on or off with the
@code{cp} request.
The number register @code{.C} is 1 if compatibility mode is on, 0 otherwise.

@findex \A
GNU @code{troff} does not allow the use of the escape sequences
@samp{\| \^ \& \@} \@{ \@key{SP} \' \` \- \_ \! \% \c} in names of
strings, macros,
diversions, number registers, fonts or environments; @sc{Unix} @code{troff} does.
The @code{\A} escape sequence may be helpful in avoiding use of these escape
sequences in names.

@cindex fractional point sizes
@cindex point sizes, fractional
@findex ps@r{, incompatibilities with Unix @code{troff}}
Fractional pointsizes cause one noteworthy incompatibility.  In @sc{Unix}
@code{troff} the @code{ps} request ignores scale indicators and so

@example
.ps 10u
@end example

will set the pointsize to 10 points, whereas in GNU @code{troff} it will set
the pointsize to 10 scaled points.
@xref{Fractional Type Sizes}, for more information.

@findex bd@r{, incompatibilities with Unix @code{troff}}
@findex cs@r{, incompatibilities with Unix @code{troff}}
@findex tkf@r{, incompatibilities with Unix @code{troff}}
@findex tr@r{, incompatibilities with Unix @code{troff}}
@findex fp@r{, incompatibilities with Unix @code{troff}}
In GNU @code{troff} there is a fundamental difference between unformatted
input characters, and formatted output characters.  Everything that
affects how an output character will be output is stored with the
character; once an output character has been constructed it  is
unaffected by any subsequent requests that are executed, including
@code{bd}, @code{cs}, @code{tkf}, @code{tr}, or @code{fp}
requests.  Normally output characters are constructed
from input characters at the moment immediately before the character is
added to the current output line.  Macros, diversions and strings are
all, in fact, the same type of object; they contain lists of input
characters and output characters in any combination.  An  output
character does not behave like an input character for the purposes of
macro processing; it does not inherit any of the special properties that
the input character from which it was constructed might have had. For
example,

@example
.di x
\\\\
.br
.di
.x
@end example

@findex \e@r{, incompatibilities with Unix @code{troff}}
@findex \!@r{, incompatibilities with Unix @code{troff}}
@findex \?@r{, incompatibilities with Unix @code{troff}}
will print @samp{\\} in GNU @code{troff}; each pair of input backslashes is
turned into one
output backslash and the resulting output backslashes are not
interpreted as escape
characters when they are reread. @sc{Unix} @code{troff} would interpret them as
escape characters when they were reread and would end up printing one
@samp{\}.
The correct way to obtain a printable backslash is to use the
@code{\e} escape
sequence: this will always print a single instance of the current escape
character, regardless of whether or not it is used in a diversion; it
will also work in both GNU @code{troff} and @sc{Unix} @code{troff}.  If
you wish for some
reason to store in a diversion an escape sequence that will be
interpreted when the diversion is reread, you can either use the
traditional @code{\!} transparent output facility, or, if this is unsuitable,
the new @code{\?} escape sequence.  @xref{Diversions}, for more information.


@node Summary,  , Implementation Differences, Programming Tutorial
@section Summary
@cindex summary

@ignore
@node geqn, gtbl, Programming Tutorial, Top
@chapter @code{geqn}
@cindex @code{eqn}
@cindex @code{geqn}


@menu
* Invoking geqn::               
@end menu

@node Invoking geqn,  , geqn, geqn
@section Invoking @code{geqn}
@cindex invoking @code{geqn}
@cindex @code{geqn}, invoking



@node gtbl, gpic, geqn, Top
@chapter @code{gtbl}
@cindex @code{tbl}
@cindex @code{gtbl}


@menu
* Invoking gtbl::               
@end menu

@node Invoking gtbl,  , gtbl, gtbl
@section Invoking @code{gtbl}
@cindex invoking @code{gtbl}
@cindex @code{gtbl}, invoking


@node gpic, grap, gtbl, Top
@chapter @code{gpic}
@cindex @code{pic}
@cindex @code{gpic}


@menu
* Invoking gpic::               
@end menu

@node Invoking gpic,  , gpic, gpic
@section Invoking @code{gpic}
@cindex invoking @code{gpic}
@cindex @code{gpic}, invoking



@node grap, grefer, gpic, Top
@chapter @code{grap}
@cindex @code{grap}



@node grefer, gsoelim, grap, Top
@chapter @code{grefer}
@cindex @code{refer}
@cindex @code{grefer}


@menu
* Invoking grefer::             
@end menu

@node Invoking grefer,  , grefer, grefer
@section Invoking @code{grefer}
@cindex invoking @code{grefer}
@cindex @code{grefer}, invoking



@node gsoelim, Devices, grefer, Top
@chapter @code{gsoelim}
@cindex @code{soelim}
@cindex @code{gsoelim}


@menu
* Invoking gsoelim::            
@end menu

@node Invoking gsoelim,  , gsoelim, gsoelim
@section Invoking @code{gsoelim}
@cindex invoking @code{gsoelim}
@cindex @code{gsoelim}, invoking



@node Devices, File formats, gsoelim, Top
@chapter Devices
@cindex devices



@menu
* Special Characters::          
* grotty::                      
* grops::                       
* grodvi::                      
* grolj4::                      
* grohtml::                     
* gxditview::                   
@end menu

@node Special Characters, grotty, Devices, Devices
@section Special Characters
@cindex special characters
@cindex characters, special


@c distribute these through the text
@xref{Font Files}.

@node grotty, grops, Special Characters, Devices
@section @code{grotty}
@cindex @code{grotty}



@menu
* Invoking grotty::             
@end menu

@node Invoking grotty,  , grotty, grotty
@subsection Invoking @code{grotty}
@cindex invoking @code{grotty}
@cindex @code{grotty}, invoking



@node grops, grodvi, grotty, Devices
@section @code{grops}
@cindex @code{grops}



@menu
* Invoking grops::              
* Embedding PostScript::        
@end menu

@node Invoking grops, Embedding PostScript, grops, grops
@subsection Invoking @code{grops}
@cindex invoking @code{grops}
@cindex @code{grops}, invoking



@node Embedding PostScript,  , Invoking grops, grops
@subsection Embedding PostScript
@cindex embedding postscript
@cindex postscript, embedding



@node grodvi, grolj4, grops, Devices
@section @code{grodvi}
@cindex @code{grodvi}



@menu
* Invoking grodvi::             
@end menu

@node Invoking grodvi,  , grodvi, grodvi
@subsection Invoking @code{grodvi}
@cindex invoking @code{grodvi}
@cindex @code{grodvi}, invoking



@node grolj4, grohtml, grodvi, Devices
@section @code{grolj4}
@cindex @code{grolj4}



@menu
* Invoking grolj4::             
@end menu

@node Invoking grolj4,  , grolj4, grolj4
@subsection Invoking @code{grolj4}
@cindex invoking @code{grolj4}
@cindex @code{grolj4}, invoking



@node grohtml, gxditview, grolj4, Devices
@section @code{grohtml}
@cindex @code{grohtml}



@menu
* Invoking grohtml::            
@end menu

@node Invoking grohtml,  , grohtml, grohtml
@subsection Invoking @code{grohtml}
@cindex invoking @code{grohtml}
@cindex @code{grohtml}, invoking



@node gxditview,  , grohtml, Devices
@section @code{gxditview}
@cindex @code{gxditview}



@menu
* Invoking gxditview::          
@end menu

@node Invoking gxditview,  , gxditview, gxditview
@subsection Invoking @code{gxditview}
@cindex invoking @code{gxditview}
@cindex @code{gxditview}, invoking
@end ignore


@node File formats, Request Index, Programming Tutorial, Top
@chapter File formats
@cindex file formats
@cindex formats, file



@menu
* gtroff Output::               
* Font Files::                  
@end menu

@node gtroff Output, Font Files, File formats, File formats
@section @code{gtroff} Output
@cindex @code{gtroff} output
@cindex output, @code{gtroff}


This section describes the format output by GNU @code{troff}.  The output
format used by GNU @code{troff} is very similar to that used by @sc{Unix}
device-independent @code{troff}.

The output format is @sc{ascii} based, as opposed to a binary format (like
@TeX{} dvi).
The output format is 8 bit clean, thus single characters can have the
eighth bit set, as can the names of fonts and special characters.

The output format consists of single command characters with attached
parameters which are separated from subsequent text by whitespace or
a newline.

The names of characters and fonts can be of arbitrary length; drivers
should not assume that they will be only two characters long (as
device-independent @code{troff} did).

When a character is to be printed, that character will always be in the
current font.
Unlike device-independent @code{troff}, it is not necessary for
drivers to search special fonts to find a character.

@table @code
@item H@var{n}
@item V@var{n}
@item h@var{n}
@item v@var{n}
@item c@var{n}
@item C@var{n}
@item @var{nn}@var{c}
@item t@var{xxx}
@var{xxx} is any sequence of characters terminated by a space or a
newline; the first character should be printed at the current
position, the the current horizontal position should be increased by
the width of the first character, and so on for each character.
The width of the character is that given in the font file,
appropriately scaled for the current point size,
and rounded so that it is a multiple of the horizontal resolution.
Special characters cannot be printed using this command.

This command is only allowed if the @samp{tcommand} line is present
in the @file{DESC} file.
@item u@var{n} @var{xxx}
@pindex DESC@r{, and @code{tcommand}}
This is same as the @code{t} command except that after printing each
character, the current horizontal position is increased by the sum of
the width of that character and @code{n}.

This command is only allowed if the @samp{tcommand} line is present
in the @file{DESC} file.
@item n@var{a}@var{b}
@item p@var{n}
@item s@var{n}
The argument to the s command is in scaled points (units of points/n,
where n is the argument to the sizescale command  in the @file{DESC} file.)
@item f@var{n}
@item x @dots{} \n
Device control.
@item D@var{c} @var{x}@dots{}\n
@end table

@subsection Device Control

The @code{x} command is normally followed by a letter or word
indicating the function to perform, followed by white space separated
arguments.

The first argument can be abreviated to the first letter.

@table @code
@item x init
@item x T
@item x res @var{n} @var{h} @var{v}
@item x H
The argument to the x Height command is also in scaled points.
@end table

The first three output commands are guaranteed to be:

@example
x T device
x res n h v
x init
@end example

@ignore
For example, the input @samp{crunchy \fH\s+2frog\s0\fP!?} will produce:

@example
... sample output here ...
@end example
@end ignore

@subsection Drawing Functions

The D drawing command has been extended.  These extensions will only be
used by GNU @code{pic} if the @samp{-x} option is given.

@table @code
...
@item Df n\n
Set the shade of gray to be used for filling solid objects to n; n must
be an integer between 0 and 1000, where 0 corresponds solid white and
1000 to solid black, and values in between correspond to intermediate
shades of gray.  This applies only to solid circles, solid ellipses and
solid polygons.  By default, a level of 1000 will be used.  Whatever
color a solid object has, it should completely obscure everything
beneath it. A value greater than 1000 or less than 0 can also be used:
this means fill with the shade of gray that is currently being used for
lines and text.  Normally this will be black, but some drivers may
provide a way of changing this.
@item DC d\n
Draw a solid circle with a diameter of d with the leftmost point at the
current position.
@item DE dx dy\n
Draw a solid ellipse with a horizontal diameter of dx and a vertical
diameter of dy with the leftmost point at the current position.
@item Dp $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub
n$\n
Draw a polygon with, for $i = 1 ,..., n+1$, the i-th vertex at the
current position $+ sum from j=1 to i-1 ( dx sub j , dy sub j )$. At
the moment, GNU pic only uses this command to generate triangles and
rectangles.
@item DP $dx sub 1$ $dy sub 1$ $dx sub 2$ $dy sub 2$ $...$ $dx sub n$ $dy sub
n$\n
Like Dp but draw a solid rather than outlined polygon.
@item Dt n\n
Set the current line thickness to n machine units.  Traditionally @sc{Unix}
@code{troff} drivers use a line thickness proportional to the current point
size; drivers should continue to do this if no Dt command has been
given, or if a Dt command has been given with a negative value of n.  A
zero value of n selects the smallest available line thickness.
@end table

A difficulty arises in how the current position should be changed after
the execution of these commands. This is not of great importance since
the code generated by GNU pic does not depend on this. Given a drawing
command of the form
@samp{\D'c $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y sub n$'}
where c is not one of c, e, l, a or ~, @sc{Unix} @code{troff} will treat each of the
$x sub i$ as a horizontal quantity, and each of the $y sub i$ as a
vertical quantity and will assume that the width of the drawn object is
$sum from i=1 to n x sub i$, and that the height is $sum from i=1 to n y
sub i$.  (The assumption about the height can be seen by examining the
st and sb registers after using such a D command in a \w escape
sequence.)  This rule also holds for all the original drawing commands
with the exception of De.  For the sake of compatibility GNU @code{troff} also
follows this rule, even though it produces an ugly result in the case of
the Df, Dt, and, to a lesser extent, DE commands.  Thus after executing
a D command of the form
@samp{Dc $x sub 1$ $y sub 1$ $x sub 2$ $y sub 2$ $...$ $x sub n$ $y sub n$\n}
the current position should be increased by $( sum from i=1 to n x sub i
, sum from i=1 to n y sub i )$.

@subsection Line Continuation

There is a continuation convention which permits the argument to the x X
command to contain newlines: when outputting the argument to the x X
command,  GNU @code{troff} will follow each newline in the argument with a +
character (as usual, it will terminate the entire argument with a
newline); thus if the line after the line containing the x X command
starts with +, then the newline ending the line containing the x X
command should be treated as part of the argument to the x X command,
the + should be ignored, and the part of the line following the + should
be treated like the part of the line following the x X command.




@node Font Files,  , gtroff Output, File formats
@section Font Files
@cindex font files
@cindex files, font


The groff font format is roughly a superset of the @code{ditroff} font
format.  Unlike the @code{ditroff} font format, there is no associated binary
format.  The font files for device @var{name} are stored in a directory
@file{dev@var{name}}.  There are two types of files: a device
description file called @file{DESC}, and for each font @var{f} a font
file called @file{@var{f}}.  These are text files; there is no associated
binary format.

@subsection @file{DESC} file format
@pindex DESC@r{ file format}

The @file{DESC} file can contain the following types of line:

@table @code
@item res @var{n}
There are @var{n} machine units per inch.
@item hor @var{n}
The horizontal resolution is @var{n} machine units.
@item vert @var{n}
The vertical resolution is @var{n} machine units.
@item sizescale @var{n}
The scale factor for pointsizes.  By default this has a value of 1.  One
scaled point is equal to one point/@var{n}.  The arguments to the
@code{unitwidth} and @code{sizes} commands are given in scaled points.
@xref{Fractional Type Sizes}, for more information.
@item unitwidth @var{n}
Quantities in the font files are given in machine units for fonts  whose
point size is @var{n} scaled points.
@item tcommand
This means that the postprocessor can handle the @code{t} and
@code{u} output commands.
@item sizes @var{s1} @var{s2}@dots{}@var{sn} 0
This means that the device has fonts at @var{s1}, @var{s2},
@dots{}@var{sn} scaled points.  The list of sizes must be terminated
by a 0.  Each @var{si} can also be a range of
sizes @var{m}-@var{n}.  The list can extend over more than one line.
@item styles @var{S1 S2@dots{}Sm}
The first @var{m} font positions will be associated with styles
@var{S1}@dots{}@var{Sm}.
@item fonts @var{n} @var{F1 F2 F3@dots{}Fn}
Fonts @var{F1@dots{}Fn} will be mounted in the font positions
@var{m}+1, @dots{}, @var{m}+@var{n} where @var{m}
is the number of styles.  This command may extend over more than one
line. A font name of 0 will cause no font to be mounted on the
corresponding font position.
@item family @var{fam}
The default font family is @var{fam}.
@item charset
This line and everything following in the file are ignored.  It is
allowed for the sake of backwards compatibility.
@end table

The @code{res}, @code{unitwidth}, @code{fonts} and @code{sizes} lines
are mandatory.  Other commands are ignored by @code{troff} but may be used
by postprocessors to store arbitrary information about the device in
the @file{DESC} file.


@subsection Font file format

@cindex font file format
A font file has two sections.  The first section is a sequence of lines
each containing a sequence of blank delimited words; the first word in
the line is a key, and subsequent words give a value for that key.

@table @code
@item name @var{f}
The name of the font is @var{f}.
@item spacewidth @var{n}
The normal width of a space is @var{n}.
@item slant @var{n}
The characters of the font have a slant of @var{n} degrees.
(Positive means forward.)
@item ligatures @var{lig1} @var{lig2}@dots{}@var{lign} [0]
Characters @var{lig1}, @var{lig2}, @dots{}, @var{lign} are ligatures;
possible ligatures are ff, fi, fl and ffl.  For backwards
compatibiliy, the list of ligatures may be terminated with a 0.  The
list of ligatures may not extend over more than one line.
@item special
The font is special; this means that when a character is requested that
is not present in the current font, it will be searched for in any
special fonts that are mounted.
@end table

Other commands are ignored by @code{troff} but may be used by postprocessors to
store arbitrary information about the font in the font file.

The first section can contain comments which start with the @samp{#} character
and extend to the end of a line.

The second section contains one or two subsections.  It must contain a
@code{charset} subsection and it may also contain a @code{kernpairs}
subsection.  These subsections can appear in any order.  Each
subsection starts with a word on a line by itself.

The word @code{charset} starts the @code{charset} subsection. The
@code{charset} line is followed by a sequence of lines. Each line
gives information for one character.  A line comprises a number of
fields separated by blanks or tabs. The format is

@display
@var{name} @var{metrics} @var{type} @var{code} @var{comment}
@end display

@var{name} identifies the character: if @var{name} is a single
character @var{c} then it corresponds to the @code{groff} input character
@var{c}; if it is of the form @samp{\@var{c}} where @var{c} is a
single character, then it corresponds to the @code{groff} input character
@samp{\@var{c}}; otherwise it corresponds to the @code{groff} input character
@samp{\[@var{name}]} (if it is exactly two characters @var{xx} it can
be entered as @samp{\(@var{xx}}.) Groff supports eight bit characters;
however some utilities has difficulties with eight bit characters.
For this reason, there is a convention that the @var{name}
@samp{char@var{n}} is equivalent to the single character whose code is
@var{n}. For example, @samp{char163} would be equivalent to the
character with @var{code} 163 which is the pounds sterling sign in ISO
Latin-1 character set.  The name @samp{---} is special and indicates
that the character is unnamed; such characters can only be used by
means of the @code{\N} escape sequence in @code{troff}.

The @var{type} field gives the character type:

@table @code
@item 1
means the character has an descender, for example, p;
@item 2
means the character has an ascender, for example, b;
@item 3
means the character has both an ascender and a descender, for example,
@samp{(}.
@end table

The @var{code} field gives the code which the postprocessor uses to
print the character.  The character can also be input to groff using
this code by means of the @code{\N} escape sequence. The code can be any
integer.  If it starts with a 0 it will be interpreted as octal; if it
starts with @code{0x} or @code{0X} it will be intepreted as hexdecimal.

Anything on the line after the @var{code} field will be ignored.

The @var{metrics} field has the form (as a single long line):

@smallexample
@var{width}[,@var{height}[,@var{depth}
  [,@var{italic_correction}[,@var{left_italic_correction}
  [,@var{subscript_correction}]]]]]
@end smallexample

There must not be any spaces between these subfields.  Missing
subfields are assumed to be 0.  The subfields are all decimal
integers.  Since there is no associated binary format, these values
are not required to fit into a variable of type @samp{char} as they
are in ditroff.  The @var{width} subfields gives the width of the
character.  The @var{height} subfield gives the height of the
character (upwards is positive); if a character does not extend above
the baseline, it should be given a zero height, rather than a negative
height.  The @var{depth} subfield gives the depth of the character,
that is, the distance below the lowest point below the baseline to
which the character extends (downwards is positive); if a character
does not extend below above the baseline, it should be given a zero
depth, rather than a negative depth.  The @var{italic_correction}
subfield gives the amount of space that should be added after the
character when it is immediately to be followed by a character from a
roman font.  The @var{left_italic_correction} subfield gives the
amount of space that should be added before the character when it is
immediately to be preceded by a character from a roman font.  The
@var{subscript_correction} gives the amount of space that should be
added after a character before adding a subscript. This should be less
than the italic correction.

A line in the @code{charset} section can also have the format

@example
@var{name} "
@end example

This indicates that @var{name} is just another name for the character
mentioned in the preceding line.

The word @code{kernpairs} starts the kernpairs section.  This contains a
sequence of lines of the form:

@display
@var{c1 c2 n}
@end display

This means that when character @var{c1} appears next to character
@var{c2} the space between them should be increased by @var{n}.  Most
entries in kernpairs section will have a negative value for @var{n}.


@ignore
@node Installation, Request Index, File formats, Top
@chapter Installation
@cindex installation
@end ignore


@node Request Index, Register Index,  File formats, Top
@chapter Request Index

@printindex fn


@node Register Index, Program Index, Request Index, Top
@chapter Register Index

@printindex vr

@ignore
@node String Index, Macro Index, Register Index, Top
@chapter String Index



@node Macro Index, Program Index, String Index, Top
@chapter Macro Index
@end ignore


@node Program Index, Concept Index, Register Index, Top
@chapter Program Index

@printindex pg



@node Concept Index,  , Program Index, Top
@chapter Concept Index

@printindex cp



@summarycontents
@contents
@bye
