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\title{The {\tt txt} Style}
\author{Ralph Droms \\ Bucknell University}

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\section{Introduction}
\TeX\ and \LaTeX\ produce nicely formatted documents; however, the final
versions of these documents, the {\tt .dvi} files, are, in some ways,
not accessible to further electronic processing. For example,
\unix\footnote{\unix\ is a trademark of AT\&T Bell Laboratories.}
tools like {\tt grep} and {\tt emacs} can't be used on {\tt .dvi}
files, and electronic display of {\tt .dvi} files requires a
high-function bit--mapped terminal.

Some text--processing systems accommodate both high--resolution output
and straight ASCII text output. Microsoft Word\footnote{I assume
Microsoft Word is a trademark of Microsoft, Inc.} can save a document
in either formatted or text--only form.  The formatted version can be
printed on an appropriate high--function printer, while the text--only
version is compatible with other tools and text editors. The \unix\
text processing tools {\tt troff} and {\tt nroff} both accept the same
input files, but {\tt troff} produces high--quality output while {\tt
nroff} produces ASCII text. {\tt troff} and {\tt nroff} are used, for
example, to produde hard--copy and online versions of the \unix\
user's manual, assuring that both versions have identical content.

\TeX\ and \LaTeX\ have no equivalent to {\tt troff}'s {\tt nroff}.
The {\tt txt} style is part of a package that can take standard
\LaTeX\ input and produce ASCII text output.  This output will not be
identical to the \LaTeX\ {\tt .dvi} file output, but will, instead, be
ASCII text appropriately formatted for an 8.5 by 11 inch page.

\section{Theory}

The problem addressed by {\tt txt} is to restrict \LaTeX\ output so
that it simulates a line printer, without rewriting \LaTeX\ itself. An
accompanying program, {\tt dvi2tty}~\cite{dvi2tty}, then produces
ASCII text output from the {\tt txt}--generated {\tt .dvi} file.

There are three primary areas in which {\tt txt} must modify \LaTeX\
to produce ASCII output:

\begin{itemize}
\item Horizontal spacing
\item Vertical spacing
\item Special characters
\end{itemize}

{\tt txt} makes a first approximation to line--printer output by
substituting the 12--point Courier font for all the standard \LaTeX\
font styles and sizes. Using 12--point Courier is assumed to be a good
approximation of a standard line printer, both horizontally and
vertically.  {\tt txt} explicitly sets the \LaTeX\
\verb+\baselineskip+ to be 12 points to better approximate a standard
line printer generating 66 lines on an 11.5 inch long page.

The next problem in approximating line printer output is to replace
all rubber vertical glue with fixed glue. Such rubber glue, included
in commands like \verb+\section+ and the {\tt itemize} environment, is
replaced by fixed glue in multiples of 12 points. Several other fixed
vertical spaces are modified to be even multiples of 12 points, again
to better simulate line printer output.

There are two types of special characters modified by {\tt txt}: the
\verb+\labelitem+ characters used by the {\tt itemize} environment and
footnote marks. Footnote marks are recoded to use arabic numbers in
parentheses without superscripting (which is typically not feasible on
a line printer or ASCII terminal). The \verb+\labelitem+ characters
are redefined to be ``{\tt o}'', ``{\tt -}'', ``{\tt *}'' and ``{\tt
+}''.

\section{Using {\tt txt}}

Generating ASCII output with {\tt txt} requires two steps: first, the
{\tt txt} style must be included in the \verb+\documentstyle+ command,
and then {\tt dvi2tty} must be run on the {\tt .dvi} file to generate
the ASCII output.

The {\tt txt} style specification should be included after any other
style files, so that previously defined commands and parameters are
correctly redefined by {\tt txt} for ASCII output. For example, the
header to this document is:
\begin{verbatim}
     \documentstyle[12pt,txt]{article}
\end{verbatim}

A sample session to generate a file containing the ASCII version of
this doucment is (where the ``\%'' character is the \unix\ prompt and
should not be typed):
\begin{verbatim}
     % latex txt.tex
     % dvi2tty txt.dvi > txt.txt
\end{verbatim}

\section{Bugs}

Not all vertical rubber glue has been removed: for example, tables,
page headers and page footers do not always appear on even multiples
of 12 point lines.

Rules aren't correct; specifically, horizontal and vertical lines in
arrays are likely not to work correctly.

The model used by {\tt dvi2tty} to simulate horizontal spaacing is
prone to error, especially when horizontal spaces or fills are used.

\section{Summary}

The {\tt txt} style generates an approximation of line printer output
from \LaTeX\ input, in the way {\tt nroff} generates output from {\tt
troff} input. The approximation assumes an 80 column, 66 line per page
printer. The {\tt .dvi} file generated by {\tt txt} can be run through
{\tt dvi2tty}.  The resulting ASCII output is compatible with
ASCII--only display and printing devices, and can be further processed
by tools like {\tt grep} and {\tt emacs}.

The approximation is imperfect and has several bugs in the spacing of
output.  Modifications to both {\tt txt}, especially eliminating
remaining rubber space, and {\tt dvi2tty} are required to generate
better output.

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