This was one of the first markup languages on the original version of Unix. Man pages are the most common examples of things formatted in *roff macros; many people swear by them, but nroff has, to me at least, a more arcane syntax than needed (see Figure 12), and probably makes a poor choice for new works. It is worth knowing, though, that you can typeset a man page directly into postscript with groff. Most man commands will do this for you with man -t foo | lpr.

.B man
is the system's manual pager. Each
.I page
argument given to 
.B man
is normally the name of a program, utility or function. 
The 
.I manual page 
associated with each of these arguments is then found and
displayed. A 
.IR section ,
if provided, will direct
.B man
to look 
only in that
.I section
of the manual.

TeX, and the macro package LaTeX, are one of the most widely used markup languages on Un*x systems, although TeX did not originate on Unix and is available to run on a wide variety of systems. Technical works are frequently written in LaTeX because it greatly simplifies the layout issues and isstill one of the few text processing systems to support mathematics both completely and well. TeX's output format is dvi, and is converted to PostScript or Hewlett Packard's PCL with dvips or dvilj. If you wish to install TeX or LaTeX, install the whole teTeX group of packages; it contains everything. Recent TeX installations include pdfTeX and pdfLaTeX, which produce Adobe PDF files directly. Commands are available do create hyperlinks and navigation features in the PDF file.

\subsubsection{NAT}

Each real server is assigned a different IP address, and the NA
implements address translation for all inbound and outbound
packets.

  \begin{description}
  \item[Advantage] Implementation simplicity, especially if we
already implement other NAT capabilities.

  \item[Disadvantage] Return traffic from the server goes through
address translation, which may incur a speed penalty.  This
probably isn't too bad if we design for it from the
beginning.

  \item[Disadvantage] NAT breaks the end-to-end semantics of normal
internet traffic.  Protocols like ftp, H.323, etc would
require special support involving snooping and in-stream
rewriting, or complete protocol proxying; neither is likely
to be practical.
  \end{description}

There is at least one free SGML parser available for Un*x systems; it forms the basis of Linuxdoc-SGML's homegrown document system. It can support other DTD's, as well, most notably DocBook. This document is written in DocBook-DTD SGML; see Figure 14 for an example.

<varlistentry>
<term>SGML</term>
<listitem>
<para>
There is at least one free SGML parser available for Un*x 
systems; it forms the basis of Linuxdoc-SGML's homegrown 
document system.  It can support other DTD's, as well, most
notably DocBook.  This document is written in DocBook-DTD 
SGML.
</para>
</listitem>
</varlistentry>