path: root/Master/texmf-dist/doc/latex/codedoc/CodeDoc-manual.tex

\ifnum\month<10 \edef\month{0\the\month}\else	\edef\month{\the\month}\fi
\ifnum\day<10	\edef\day{0\the\day}\else \edef\day{\the\day}\fi

\documentclass[article(a4paper),
index,% Comment this out if you don't want an index
%obeystop,% Uncomment this if you don't want to print the implementation
%produce,% Uncomment this to produce 'codedoc.cls'
]{codedoc}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Definitions for the example environments

\def\bluecolor{blue!75!white}
\def\redcolor{red!75!white}
\def\yellowcolor{yellow!75!white}

\newcount\colorcount

\def\tryblue{%
	\ifnum\colorcount=\inputlineno%
		\let\incolor\bluecolor%
		\def\commentcolor{white}%
		\ifodd\inputlineno%
			\let\outcolor\redcolor%
			\let\filcolor\yellowcolor%
		\else%
			\let\outcolor\yellowcolor%
			\let\filcolor\redcolor%
		\fi%
	\else%
		\advance\colorcount by1\relax%
		\expandafter\tryred%
	\fi}

\def\tryred{%
	\ifnum\colorcount=\inputlineno%
		\let\incolor\redcolor%
		\def\commentcolor{white}%
		\ifodd\inputlineno%
			\let\outcolor\yellowcolor%
			\let\filcolor\bluecolor%
		\else%
			\let\outcolor\bluecolor%
			\let\filcolor\yellowcolor%
		\fi%
	\else%
		\advance\colorcount by1\relax%
		\expandafter\tryyellow%
	\fi}

\def\tryyellow{%
	\ifnum\colorcount=\inputlineno%
		\let\incolor\yellowcolor%
		\def\commentcolor{gray}%
		\ifodd\inputlineno%
			\let\outcolor\bluecolor%
			\let\filcolor\redcolor%
		\else%
			\let\outcolor\redcolor%
			\let\filcolor\bluecolor%
		\fi%
	\else%
		\advance\colorcount by1\relax%
		\expandafter\tryblue%
	\fi}

\newdimen\csize
\csize15cm 

\newskip\exskip
\exskip=2em plus 1em minus 1em\relax

\newif\iftrycolor
\trycolortrue

\NewExample[]{ex0}{\ttfamily#}{#}{%
	\vskip\exskip%
	\iftrycolor%
		\tryblue%
	\else%
		\global\trycolortrue%
	\fi%
  \fboxsep6pt%
	\fboxrule4pt%
	\noindent\hfil\fcolorbox{black}{\incolor}{%
		\parbox{\csize}{\CodeInput}}%
	\global\csize15cm\relax%
	\vskip\exskip\relax}

\NewExample{ex1}{\ttfamily#}{}{}

\newdimen\exdimen
\def\getnumber#1#2#3#4!{%
	\ifnum\inputlineno<1000 %
		\exdimen#3#2pt\def\movefil{\hskip-.#2\wd\filbox}\relax%
	\else%
		\exdimen#4#3pt\def\movefil{\hskip-.#3\wd\filbox}\relax%
	\fi}

\newbox\inbox
\newbox\outbox
\newbox\filbox
\newdimen\outdimen
\outdimen30pt


\NewExample[visibleEOL]{sidebyside}{\ttfamily#}{#}{%
	\expandafter\getnumber\the\inputlineno!
	\iftrycolor%
		\tryblue%
	\else%
		\global\trycolortrue%
	\fi%
	\vskip\exskip%
	\noindent
  \fboxsep6pt%
	\fboxrule4pt%
	\setbox\inbox=\hbox{\fcolorbox{black}{\incolor}{%
		\vbox{%
		\hsize.47\hsize%
		\CodeInput}}}%
%
	\setbox\outbox=\hbox{\fcolorbox{black}{\outcolor}{%
		\vtop{%
			\hsize.3\hsize%
			\parindent0pt%
			\vskip1em\CodeOutput\vskip1em}}}%
%
	\setbox\filbox=\hbox{\fcolorbox{black}{\filcolor}{%
		\hbox to.15\ht\inbox{%
			\color{\filcolor}\vrule height.15\ht\inbox depth0pt width0pt\hss}}}%
%
	\hfil\unhcopy\inbox%
	\movefil%
	\ifdim\exdimen>.5\ht\inbox\relax\raise.4\ht\inbox\copy\filbox\else\raise.2\ht\inbox\copy\filbox\fi%
	\hskip-\fboxrule\raise\exdimen\box\outbox%
	\vskip\exskip\relax}

\def\InvisibleSpace{\catcode`\ =10\relax}
\def\cdcomment#1{\textcolor{\commentcolor}{\emph{#1}}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Definitions to print macro names

\def\macrotopskip{\goodbreak\vskip1em plus .2em minus .2em}

\def\maccolor{red!70!black}
	
\def\OneMac#1{\macrotopskip\noindent\textcolor{\maccolor}{\llap{\textbullet\ }\ttfamily#1}\par\nobreak\noindent\ignorespaces}
\def\TwoMac#1{\noindent\textcolor{\maccolor}{\llap{\textbullet\ }\ttfamily#1}\par\nobreak}
\let\PrintMacro\OneMac

\IgnorePrefix{cd@}
\def\PrintPrefix{\textcolor{gray}}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% Opening the file

\Header
{%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

This is the CodeDoc class, produced by itself
with the `produce' option on, from `\jobname.tex'.

Date: \FileDate
Version: \FileVersion
Author: Paul Isambert

The documentation can be found in `\jobname.pdf'
(you can produce it with `\jobname.tex' without the
`produce' option).

This file is published under the LaTeX Project Public License.

Comments, suggestions, bugs and, of course, NOTES:
zappathustra@free.fr

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%}

\ProduceFile{codedoc.cls}[codedoc][v.0.3][\the\year/\month/\day]
\AddBlankLine\AddBlankLine\AddBlankLine

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% The ladybug

\def\makecox(#1,#2,#3,#4)#5{%
	\vbox to0pt{\vskip-#3%
	\hbox to0pt{\hskip#2%
	\rotatebox[origin=c]{#1}{\coccinelle}\raise#5\hbox{\vbox{\everypar{}\vskip-5pt\tiny\sffamily\noindent#4}}\hss}\vss}}

\def\coxx[#1](#2,#3,#4,#5){\makecox(#2,#3,#4,#5){#1}\index{Zmakecox(240,0pt,8pt,What am I\\doing here?){0pt}\hskip1.8cm|hyperpage}}

\def\cox#1{%
	\ifx#1[%
		\def\next{\coxx[}%
	\else%
		\def\next{\coxx[0pt](}%
	\fi\next}

\def\coccinelle{%
	\bgroup%
		\setbox0=\hbox{\Huge\textbullet\llap{\raise-.4pt\hbox{\textbullet}}}
		\color{black}%
		\setbox1=\hbox{\textbullet}
		\leavevmode\raise8.5pt\hbox to0pt{\hskip.5\wd0\hskip-.47\wd1\textbullet\hss}%
		\Huge\color{red}%
		\unhcopy0%
		\hskip-\wd0%
		\color{black}%
		\raise3pt\rlap{\color{red!80!black}\hskip.47\wd0\vrule height7.5pt depth1.5pt}%
		\raise3pt\rlap{\hskip.5pt.}%
		\raise6pt\rlap{\hskip1.5pt.}%
		\raise2.5pt\rlap{\hskip5pt.}%
		\raise7.5pt\rlap{\hskip5.8pt.}
	\egroup}%

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usepackage[T1]{fontenc}
\usepackage[textwidth=16cm,textheight=24cm]{geometry}
\usepackage{xcolor}
\usepackage{graphicx}
\usepackage{silence}% This avoids tens of `Marginpar on page X moved'
\WarningFilter{latex}{Marginpar on page}% messages. Nothing vital, however.
\let\next\relax
\expandafter\ifx\csname pdfoutput\endcsname\relax
	\ClassWarningNoLine{CodeDoc}{%
		Because of numerous color manipulations,\MessageBreak
		This documentation looks better in PDF.\MessageBreak
		Give it a try}
\else%
	\ifnum\pdfoutput=1 %
		\def\next{\usepackage[pdfborder=0 0 0]{hyperref}}
	\else
		\ClassWarningNoLine{CodeDoc}{%
			Because of numerous color manipulations,\MessageBreak
			This documentation looks better in PDF.\MessageBreak
			Give it a try}
	\fi
\fi\next



\ShortVerb"
\VerbCommand§¤£
\VerbBreak¨

\def\CD{\textsf{CodeDoc}}
\def\eTeX{$\varepsilon$-\TeX}
\let\Part\part
\def\part{\clearpage\Part}

\title{The \textsf{CodeDoc} class\\\FileVersion\\\FileDate}
\author{Paul Isambert\\\texttt{zappathustra@free.fr}}
\date{}








\begin{document}

\maketitle

\vfil
{\fboxrule4pt %
\hfil\fcolorbox{black}{blue}{\hbox to4cm{%
	\Huge\scshape\raise.2cm\hbox{C}\hfil\raise.2cm\hbox{o}\hfil\raise.2cm\hbox{d}\hfil\textcolor{blue}{e}\hfil\vbox to1cm{\vfil}}}%
\kern-1.5cm\raise.3cm\hbox{\fcolorbox{black}{yellow}{\hbox to.5cm{%
	\Huge\raise.6cm\hbox{\&}\hfil\vbox to1.8cm{\vfil}}}}%
\kern-.3cm\raise1.7cm\hbox{\fcolorbox{black}{red}{\hbox to2cm{%
	\Huge\scshape D\hfil o\hfil c\hfil\vbox to2cm{\vfil}}}}%
\cox(240,-3.2cm,3.1cm,\hskip-5pt???)}

\vfil
\noindent\CD\ is a class designed to produce \LaTeX\ files
such as packages and classes along with their documentations. It does not
depart from \LaTeX's ordinary syntax, unlike e.g. \textsf{DocStrip}, 
allows any existing class to be loaded with its options and
offers various fully customizable verbatim environments that 
allows authors to typeset the code and documentation of
their files as they want. To create the documentation,
we compile the document as usual; to create the external file(s),
we simply put "produce" in the class options and compile as before.

Despite my earliest expectations, \CD\ is not better than
\textsf{DocStrip}. It is simply different. If you want
a well-delimited approach to literate programming, use
\textsf{DocStrip}. On the other hand, \CD\ is more natural,
in the sense that it is ordinary \LaTeX\ all the way down.
Note that you can `mimick' \textsf{DocStrip}, either by
putting any character at the beginning of each line of
your code and setting the "\Gobble" parameter to 1 (this
would be `inverted \textsf{DocStrip}'), or by setting
the comment character to be of category 9 (`ignored')
and beginning each line of the documentation with this character.
In this latter case, only commands that are considered by
\CD\ when producing a file should not be commented out...
but I'm going too fast here, and you should learn the basics
first...

\vskip1em
\noindent \CD\ is still in its infancy, as indicated by
its version number. Although it has passed the test of producing
this documentation, countless bugs will probably be reported,
and meaningful suggestions will be made. Be patient, and
send them to me. \emph{Any reported bug and meaningful
suggestion will be rewarded by a musical note, played by
a virtual instrument, and sent in the mp3 format.} Isn't
it amazing? I know it is. I will have to hire musically
educated secretaries to face the consequences of such
a reckless proposition. But it is worth it. Once a stable
version is reached, I might even write a symphony.\footnote{%
`Meaningful suggestion' and `stable version' are fuzzy terms,
you complain. Of course they are. Give me a chance!}

Some of the ideas of this class are not mine; some were
inspired by others; some are mine but were independantly
implemented in other places; may all these people be
thanked, as well as all the verbatim wizards around the world.
And, oh, yeah, some ideas are mine, too.
\thispagestyle{empty}
\pagebreak

\strut\vfill
\noindent\hfil\fbox{\begin{minipage}{13cm}
\noindent\textbf{Changes in version 0.3}

$\Rightarrow$ Fixed "\bslash ProduceFile", which ruined
everything in produce mode when used without optional arguments.

\noindent\textbf{Changes in version 0.2}

$\Rightarrow$ Bug fix to make "\bslash ref" work properly in
the unmodified "code" environment.

$\Rightarrow$ Files "\bslash input" and read in "produce" mode
won't produce error messages anymore... at least with \eTeX.
\end{minipage}}
\thispagestyle{empty}
\pagebreak

\strut\vfil
\tableofcontents
\vfil
\thispagestyle{empty}
\pagebreak

\part{User's manual}

\section{Code \& Documentation}

The source of this documentation looks roughly like this:
\csize10cm
\begin{ex0}
\documentclass[article(a4paper),
%produce, 
]{codedoc}

§cdcomment¤Preamble of the document£

\begin{document}
\section{Code \& Documentation}
The source of this document...

\ProduceFile{codedoc.cls}[codedoc][v.0.3][2010/03/30]
\begin{code}
	§cdcomment¤Material here will be written to codedoc.cls£
	§cdcomment¤and typeset verbatim in the documentation.£
\end{code}

\ShortCode/
/
	§cdcomment¤This too...£
/

\begin{invisible}
  §cdcomment¤This material will be written to codedoc.cls£
  §cdcomment¤but not typeset in the documentation.£
\end{invisible}

\end{document}
\end{ex0}

Everything between "\begin{code}" and "\end{code}" is written
verbatim to the dvi file. It is also the case for everything
between two "\ShortCode" symbol, in this example `"/"'. Finally,
if the comment sign at the beginning of the second line were
removed, thus enabling the "produce" option, then this code
would be written to "codedoc.cls" and no documentation would
be produced. This is \CD's basic mechanism. Let's
review it more precisely. In what follows, I will say `normal
mode' if the "produce" option is not turned on, that is when
we're typesetting the documentation, and `produce mode' otherwise,
that is when \texttt{produce} is present among the class options and
\CD\ is used to create an external file.

The first two sections of this manual explain how \CD\ works
and provide many examples.
The third section lists all commands in alphabetical order, 
and explains what they do in each mode in a more systematic
fashion.




\subsection{Writing code}

\DescribeMacro{\ProduceFile\marg{File}\oarg{File name}\oarg{File version}\oarg{File date}}
\noindent In normal mode, this macro provides four commands:
"\FileSource" stores \meta{File}, and the next three arguments
are stored in "\FileName", "\FileVersion" and "\FileDate"
respectively. Those are optional, as indicated by their syntax.

In produce mode, \CD\ opens \meta{File} and writes to it everything
in a "code" environment. "\FileName", "\FileVersion" and "\FileDate"
are also provided and may be used in "\Header" (see below) or in the
file itself with "\CodeEscape" (see page \pageref{CodeEscape}). Thus, you can avoid
mismatches between your documentation and the "\ProvidesPackage" declaration,
for instance.

\DescribeMacro{\CloseFile\marg{File}}
\noindent In produce mode, when the "autoclose" option is on, "\ProduceFile"
closes the file that was currently under production, if any. But you
might want to keep a file open, in case you're writing to several files
at the same time. That's why \CD's basic behavior is to keep all files
open. Thus

\csize5cm
\begin{ex0}
\ProduceFile{myfile}
\begin{code}
\def\foo{%
\end{code}

\ProduceFile{myotherfile}
\begin{code}
\relax
\end{code}

\ProduceFile{myfile}
\begin{code}
	FOO}
\end{code}
\end{ex0}

\begin{ex1}
\def\foo{%
	FOO}\end{ex1}

\noindent will write \fbox{\parbox{2cm}\CodeInput} to "myfile" and
"\relax" to "myotherfile". This might not be very good practice,
but who knows? that might be useful when building a complicated package.

But \TeX\ cannot keep open as many files as one wants. Actually, \CD\
will start complaining when more than 16 files are simultaneously in
production. "\CloseFile" is used to close those whose production is
over and allocate their streams to new files.\cox(240,4pt,12pt,Do files flow?)

\DescribeEnvironment{code}
This is the basic environment that writes its content to an external
file in produce mode or displays it verbatim in the documentation in
normal mode. There is nothing much to say. Each line is numbered,
as one generally wants the implementation of a code to be. One important
thing is that everything on the line after "\begin{code}" will be gobbled.
"\end{code}" can appear wherever you want.

\DescribeMacro{\CodeFont\marg{Font specifications}}
The font of the "code" environment may be changed with "\CodeFont"
(by default, it's "\ttfamily"). Since everything is in a group,
you can use `spreading commands'.

\DescribeMacro{\LineNumber\{code\}\marg{Font specifications}\marg{Width}\oarg{Number}}
This sets the style of the line number, the width of the box it is put in (by default,
it's "0pt", so numbers are in the left margin), and the starting value. The first argument
is "code" and not \meta{code}, because "\LineNumber" is a macro that applies to
all "example" environments (see the next section), and its first argument is the name
of the environment to modify. By default, "code" is not an "example" environment (although
it might be redefined as such) but this command is nonetheless available.

\trycolorfalse
\let\incolor\redcolor \let\outcolor\yellowcolor \let\filcolor\bluecolor
\begin{sidebyside}
\CodeFont{\color{red}\itshape}
\LineNumber{code}{\ttfamily\footnotesize¨\color{green}}{2cm}[25]
\begin{code} This will be gobbled
\def\foo{%
	FOO}
\end{code}
\end{sidebyside}

\noindent Note that "\LineNumber" inherits the specification of "\CodeFont" that it
doesn't override, in this example the italic shape. The "\color" command does \emph{not}
belong to \CD, but to the \textsf{xcolor} package. If you want to do really interesting
things with "code", it is better to redefine it as an "example" (see next section).

As usual with "verbatim" environments, there exists a starred version of "code"
that shows spaces.

\DescribeEnvironment{invisible}
In normal mode, everything in a "invisible" environment is skipped. In produce mode,
however, the material is written to the file in production. This is useful to
write code you don't want to comment in the documentation, like specifications
at the beginning of the file or repetitive macro definitions. As you might imagine,
there is no starred variant.

\DescribeMacro{\Header\marg{Text}}
In produce mode, unless the "noheader" option is on, \CD\ writes the following at the
beginning of every file:

\begin{ex1}
% This is §meta¤\FileName£, produced by the CodeDoc class
% with the `produce' option on.
%
% To create the documentation, compile §meta¤jobname.tex£
% without the `produce' option.
%
% SOURCE: §meta¤File (\input in File...)£
% DATE: §meta¤\FileDate£
% VERSION: §meta¤\FileVersion£
\end{ex1}
\CodeInput

\noindent where "\FileName", "\FileDate" and "\FileVersion" are set by "\ProduceFile".
The `"\input in file"' part is optional and recursive, depending on files "\input" in
your document. With "\Header", you can change this and print \meta{Text} instead.
In \meta{Text}, ends of line are obeyed, and a comment sign followed by a space
will start every line. Comment signs are normal sign.
"\Header" should appear before "\ProduceFile".

\DescribeMacro{\AddBlankLine}
In produce mode, \CD\ writes a blank line to the file under production. Useful
to delimit macros.

\DescribeMacro{\TabSize\marg{Number}}
This is the number of spaces by which a tabulation will be represented in verbatim
context. Default is~2. In produce mode, however, tabs are written as tabs, so this
parameter has no effect.

\DescribeMacro{\Gobble\marg{Number}}
The number of characters that will be gobbled at the beginning of each line. This
works both in normal mode and in produce mode. This might be useful to indent code
lines to make them more visible. When gobbling, a tab is considered as a single
character and not as \emph{n} characters, \emph{n} being the value of "\TabSize".

A totally blank line is written as a totally blank line in both modes, i.e. \CD\
does not fill its need for gobbled characters on the next line. The "\end{code}"
line doesn't need to be indented, although it can be. If there are more characters
than the value of "\Gobble" before "\end{code}", then a new line is created.

\LineNumber{code}{\ttfamily\footnotesize}{1em}[1]
\CodeFont{\ttfamily}
\begin{sidebyside*}
\TabSize{3}
\Gobble{2}
§bgroup§InvisibleSpace§cdcomment¤My own value for \TabSize is 2,
hence the 2-space tab here,
but in the right panel it's 3£§egroup
\begin{code*}
12\foo   \foo

12\foo	\foo
\end{code*}
\end{sidebyside*}

\DescribeMacro{\BoxTolerance\marg{Dimension}}
Verbatim lines often go into the right margin. This is the threshold above
which \TeX\ reports an overfull box. Default is 0pt.




\subsection{Macros to describe macros}

Most of the commands in this section are similar to those in \textsf{DocStrip}.
\CD\ has an indexing mechanism that simply uses \textsf{MakeIndex}; if the "index" option
is on, the "makeidx" package is loaded and "\makeindex" is executed. This also
means that "\printindex" is available. \CD\ does not require a special style file
for \textsf{MakeIndex}. Thus, users can compile a documentation made with \CD\
with \textsf{MakeIndex}'s default specifications.

\let\PrintMacro\TwoMac

\macrotopskip
\DescribeMacro{\DescribeMacro\marg{Macro}}
\DescribeMacro{\DefineMacro\marg{Macro}}
\noindent These commands print their argument according to "\PrintMacro" (see below).
The first token is "\stri§-ng"'ed,%
\footnote{Verbatim text does not break by itself. I've used \texttt{\bslash VerbCommand}
here (see below) to include a discretionary.}
so it can be a control sequence. They also create
an index entry with the first token, and here lies their difference: they print the
page number differently to distinguish whether a macro is described or defined (in the
implementation). By  default "described" macros have normal page numbers while
"defined" macros have theirs in italics. This is not conventional, I agree, but
it can be changed.\footnote{Since \CD\ doesn't index macros when \emph{used} in the
code, I've found this choice more readable.}

\macrotopskip
\DescribeMacro{\DescribeEnvironment\marg{Environment}}\nobreak
\DescribeMacro{\DefineEnvironment\marg{Environment}}\nobreak
\noindent This is similar to the "macro" version above, except that the entry is followed
by `(environment)' in the index.

\macrotopskip
\DescribeMacro{\DescribeIndexFont\marg{Font specifications}}
\DescribeMacro{\DefineIndexFont\marg{Font specifications}}
\noindent This sets how the page numbers are printed for "described" and "defined" macros
(and environments) respectively.\cox[6pt](110,6cm,40pt,Don't you find these\\names confusing?)
\marg{Font specifications} should be commands like "\ttfamily" and not argument-taking
commands like "\texttt". You know that if you use \textsf{MakeIndex}.

\let\PrintMacro\OneMac
\DescribeMacro{\PrintMacro\marg{Macro or environment}}
This is the command that typeset the ("\string"'ed) macro. It takes one argument.
It is shown here not to use it as is but to redefine it. Its default definition is:

\csize8cm
\begin{ex0}
\def\PrintMacro#1{%
	\noindent%
	\marginpar{\raggedleft\strut\ttfamily#1}%
	\ignorespaces}
\end{ex0}

\noindent That is, it puts the macro in the margin. (Obviously, it was redefined in this documentation.)
To achieve the same effect as with \textsf{DocStrip}, the following command is needed.

\DescribeMacro\DocStripMarginpar
This reverses marginpar and sets the right value for "\marginparpush" and "\marginparwidth".
They weren't included by default because you have the right to do what you want
with your margins.

\DescribeMacro{\IgnorePrefix\marg{Macro prefix}}
Many package and class authors prefix their internal commands with a string
of letters to avoid clashes with other packages. For instance, if one writes
a package "mypack", one may name all internal commands "\mp@foo", "\mp@boo",
"\mp@moo", etc. Unfortunately, when indexed, they will all end up in the `M'
letter, whereas one might want to have them sorted without the prefix,
with "\mp@foo" indexed as if it was "\foo", etc. This is what "\IgnorePrefix"
does; when sorting entries produced by "\DescribeMacro" and "\DefineMacro",
\meta{Macro prefix} is ignored, although it is printed of course as part
of the name. In our example, one would say "\IgnorePrefix{mp@}".
This command has two restrictions: first, \meta{Macro prefix} should be
no more than 8 characters long; second, any macro described with
"\DescribeMacro" or "\DefineMacro" should have as many characters as
"\IgnorePrefix", 3 in our example. A simple way to circumvent the latter
shortcoming is to temporarily define \meta{Macro prefix} as an empty string:

\csize9cm
\begin{ex0}
\IgnorePrefix{mp@}
\DefineMacro\mp@foo §cdcomment¤Will be indexed as \foo£

\DefineMacro\fo §cdcomment¤This will cause an error message£

\IgnorePrefix{}
\DefineMacro\fo §cdcomment¤This is perfectly ok£
\IgnorePrefix{mp@}
\end{ex0}

\noindent You can have several "\IgnorePrefix" specifications, they
are effective for the macros that follow them. For instance, some
macros in \CD\ are prefixed with "cd@@", and when I define them
in this documentation I specify "\IgnorePrefix{cd@@}" and then
immediately "\IgnorePrefix{cd@}", which is the normal prefix.

\DescribeMacro{\PrintPrefix\marg{Macro prefix}}
Like "\PrintMacro", this command is not shown here to be used but
to be redefined. It is put just before \meta{Macro prefix} when
printing the index, so that you can typeset it differently. For
instance, most \CD's internal macros are prefixed with "cd@".
I have specified "\IgnorePrefix{cd@}" for this documentation
and defined "\PrintPrefix" as "\def\PrintPrefix{\textcolor{gray}}"
so that all prefixes are printed in gray (thanks to the \textsf{xcolor}
package). For instance, "\cd@BadChar" is printed "\"{\color{gray}"cd@"}"BadChar"
in the index (which you can verify if the "obeystop" option is commented out,
thus including the implementation in the documentation).
Obviously, "\def\PrintPrefix#1{\textcolor{gray}{#1}}" would have
been equally efficient. Just note that since "\PrintPrefix" is
"\let" to "\relax" by default, you have to use "\newcommand"
and not "\renewcommand" when defining it for the first time,
in case you prefer \LaTeX's command definitions.

\let\PrintMacro\TwoMac
\macrotopskip
\DescribeMacro{\meta\marg{Argument}}
\DescribeMacro{\marg\marg{Argument}}
\DescribeMacro{\oarg\marg{Argument}}
\DescribeMacro{\parg\marg{Argument}}
\noindent These are well-known. In case you've forgotten:

\noindent"\meta{Argument}" $\Rightarrow$ \meta{Argument}\par
\noindent"\marg{Mandatory argument}" $\Rightarrow$ \marg{Mandatory argument}\par
\noindent"\oarg{Optional argument}" $\Rightarrow$ \oarg{Optional argument}\par
\noindent"\parg{Picture argument}" $\Rightarrow$ \parg{Picture argument}

\let\PrintMacro\OneMac
\DescribeMacro\bslash
Everybody needs a backslash. This one is meant to print
equally well in usual contexts and in PDF bookmarks created
by \textsf{hyperref}, if any. So it can be used in titles
without restriction.

\DescribeMacro{\StopHere\marg{Code}}
If the "obeystop" command is on, \CD\ will execute \meta{Code} and then "\end{document}",
otherwise nothing happens.
If the "index" option is also on, "\printindex" will be automatically executed after \meta{Code}.
This is useful to let the user print a version of the documentation with some part(s)
left out, typically the implementation.


\subsection{Choosing the class}
\CD\ by itself defines nothing that one wants a class to define. It lets the
user call the desired class. To do so, just add the name of the class in the
options of the "\documentclass" declaration. If you want the class to load
options itself, put them after the name of the class, between parenthesis,
and separated by semi-colons. Thus, "\documentclass[memoir]{codedoc}" loads
the \textsf{memoir} class without options while "\documentclass[memoir(a4paper;oneside)]{codedoc}"
loads it with the "a4paper" and "oneside" options.%
\footnote{This means that if you specify an unknown option for
\CD, it will try to load an (probably) unknown class, and you
will get the corresponding error message.}

By default, \CD\ loads the \textsf{article} class without options.







\subsection{Dangerous strings}\label{dangerous}
In produce mode, \CD\ becomes a string tester and nothing else.\cox(160,-5cm,30pt,\hskip-10pt Daaaaaaangerouuuuuus...)
Hence, there are strings you don't want it to see because you don't want it to execute
them. For instance, you don't want "\end{document}" to be executed
unless at the end of the document. So when you say "\verb+\end{document}+",
you want \CD\ to identify that "\end{document}" is not for real. 
Fortunately, \CD\ does so. To some extent.

More precisely, \CD\ identifies its own verbatim commands (described in the
next section), \LaTeX's "\verb" and "verbatim" environment, as well as
verbatim environments created with the "fancyvrb" package and the `short
verb' characters defined with "\DefineShortVerb" from the same package.
Thus, you can safely use "fancyvrb" and its companion "fvrb-ex".

However, "\begin"'s and "\end"'s are not the only strings that must be
used carefully. The most important things you want \CD\ to ignore
in case they shouldn't be executed are its own macros. For instance, you
don't want "\ProduceFile" to be executed when there's no reason to do so.
But, unless you're documenting \CD\ itself, what might be the situation
where "\ProduceFile" is executed wrongly? Simply if you use it in a statement with
"\let", "\def", "\newcommand", etc. In produce mode, \CD\ does not recognizes
these commands and for instance in "\let\ProduceFile\mycommand", "\let" will
be skipped and "\ProduceFile" executed. Hence the following.

\DescribeMacro{\DangerousEnvironment\marg{List of environments}}
Whenever you want \CD\ to skip an environment in produce mode, for instance
because it's a verbatim environment designed by yourself, you can add
its name to "\DangerousEnvironment". If you add more than one name,
use commas as separators.

\let\PrintMacro\TwoMac
\macrotopskip
\DescribeMacro{\StartIgnore}
\DescribeMacro{\StopIgnore}
\noindent In produce mode, when \CD\ encouters "\StartIgnore", everything
is skipped until "\StopIgnore" is found. This is useful to hide parts of
your document that are irrelevant to the file you're building in produce
mode (which is probably contained in the `implementation' section). You should
be careful to define your "example" environments and other verbatim devices
outside the skipped material, if you want \CD\ to identify them properly
when it stops ignoring things.

\csize12cm 
\begin{ex0}
\DangerousEnvironment{myenv,myotherenv}
\begin{myenv}
\end{document} §cdcomment¤This will be skipped by §CD£
\end{myenv}

\StartIgnore
\let\ProduceFile\myproduce §cdcomment¤This too, but that will be taken into£
                           §cdcomment¤account in normal mode£
\StopIgnore
\end{ex0}

However, you should be aware of the following points:

\noindent\llap{\textbullet\ }\emph{Any command that has some effect in produce mode should
appear verbatim in your document}.

\noindent Conversely,

\noindent\llap{\textbullet\ }\emph{Commands that have some effect
in produce mode cannot be redefined for that mode}.

\noindent And when I say `cannot', I mean `you can try, it won't work'. This leads
to the final principle:

\noindent\llap{\textbullet\ }\emph{You can redefine a command to have the desired effect in normal mode
as long as you respect its arguments, so that it can work properly in produce
mode. And this should be done between} "\StartIgnore" \emph{and} "\StopIgnore"\emph{, of course.}

For instance, you can say:

\csize8.8cm
\begin{ex0}
\StartIgnore
\renewcommand\CloseFile[1]{End of #1\clearpage}
\StopIgnore
\end{ex0}

\noindent and when you say "\CloseFile{myfile}", `"End of myfile"' will be printed to
the documentation, and a new page will be created, while in produce mode \CD\ will
do its usual job. On the other hand, although "\let\cf\CloseFile" is meaningful in
normal mode, in produce mode it won't take effect, i.e. \CD\ won't close anything.
Finally, the previous example would have been catastrophic without "\StartIgnore"
and "\StopIgnore", because in produce mode, \CD\ would have tried to execute "\CloseFile".

"\StartIgnore" and "\StopIgnore" are also useful to make \CD\ go faster and avoid errors,
if you use it with "\input". For instance, the following file would be perfect, provided
everything that should be written to an external file is contained in "implementation.tex"

\csize13cm
\begin{ex0}
\documentclass{codedoc}
§cdcomment¤Write your verbatim definitions here, so that §CD§ can see them£
\begin{document}

\StartIgnore
\input{documentation}
\StopIgnore
\input{implementation}

\end{document} 

\end{ex0}

\noindent This example leads us to the final restriction:

\noindent\llap{\textbullet\ }\emph{You should use} "\input" \emph{in the \LaTeX's way, i.e.}
"\input{myfile}"\emph{, and not in \TeX's original way, i.e.} "\input myfile"\emph{,
if the file in question is to be read in produce mode.} In the example above,
"documentation" can be "\input" as you want, but "implementation" should be
"\input" as shown.

To know what commands have some effect in produce mode, see the summary of commands.



\section{Verbatim Madness}
\subsection{Example environments}
\let\PrintMacro\TwoMac
\DescribeEnvironment{example}
\DescribeMacro\CodeInput
\DescribeMacro\CodeOutput
\noindent At first sight, the "example" environment is totally useless. Indeed, the following
code does nothing:

\csize3cm 
\begin{ex0}
\begin{example}
\TeX
\end{example}
\end{ex0}

\noindent However, it provides two commands "\CodeInput" and "\CodeOuput". The former
prints the code verbatim (and in typewriter font), and the latter executes it. So in the end it's very useful
to document your package or class, because it avoids typing the code twice (and therefore
errors are avoided).

\begin{sidebyside}
\begin{example}
\TeX
\end{example}
\CodeInput\noindent yields \CodeOutput.
\end{sidebyside}

The "example" environment is just one instance of a family of environments that you can
create by yourself with the following commands.

\macrotopskip
\DescribeMacro{\NewExample\oarg{Options}\marg{Name}\marg{Code input}\marg{Code output}\marg{Immediate execution}}
\DescribeMacro{\RenewExample\oarg{Options}\marg{Name}\marg{Code input}\marg{Code output}\marg{Immediate execution}}
\noindent These two macros (whose difference is similar to the one between "\newcommand" and "\renewcommand")
create an environment \meta{Name} that will provide two commands, "\CodeInput" and "\CodeOutput",
whose effect is defined by \meta{Code input} and \meta{Code output}. Moreover, \meta{Name}
will execute \meta{Immediate execution}.

\meta{Code input} and \meta{Code output} have a peculiar syntax. The code to be processed
is represented by~"#". For instance, the "example" environment is defined as:

\begin{ex0}
\NewExample{example}    §cdcomment¤This is §meta¤Name££
           {\ttfamily#} §cdcomment¤\CodeInput yields but the code in typewriter font£
           {#}          §cdcomment¤\CodeOutput simply executes the code£
           {}           §cdcomment¤Nothing is done when §emph¤example£ is called£
\end{ex0}

You can do whatever you want. The code, represented by "#", may be the argument
of a macro. For instance:\cox(220,0pt,6pt,`Hello, world', what a \emph{clich\'e}!)

\eTeXOff
\begin{sidebyside}
\NewExample{myex}
           {\ttfamily\underline{#}}
           {}
           {\CodeInput}
\begin{myex}
Hello, world!
\end{myex}
\end{sidebyside}
\eTeXOn

\noindent What does "myex" do? It sets the verbatim code in typewriter font
and underlines it (which is admittedly not the most interesting thing you can do).
\meta{Code output} is empty, so "\CodeOutput" will yields nothing. Finally,
\meta{Immediate execution} calls "\CodeInput", so there's no need to call it
after the environment.

The following points apply:

\noindent\llap{\textbullet\ }All environments thus defined have a starred variant
that shows spaces as characters.

\noindent\llap{\textbullet\ }"\CodeInput", "\CodeOuput" and \meta{Immediate execution} are
groups, so you can put any command in them, they won't spread. For instance, in 
"myex" above, there's no need to add a group to restrict the application
of "\ttfamily".

\noindent\llap{\textbullet\ }"\CodeOuput" \emph{really} executes your code. Any error
will appear as such.

\noindent\llap{\textbullet\ }Since "\CodeOuput" is a group, the definition you make
won't work for the rest of your document, unless you make them global. For instance:

\csize5cm
\begin{ex0}
\NewExample{myex}{}{#}{}

\begin{myex}
\def\foo{FOO!}
\end{myex}

\CodeOutput
\foo
\end{ex0}

\noindent will yield an error message, because "\foo" was only locally defined in
"\CodeOuput".

\noindent\llap{\textbullet\ }Everything on the same line after the "\begin" statement
of an environment will be gobbled.

\noindent\llap{\textbullet\ }By default, \CD\ does not add any space or "\par" before
"\CodeInput", "\CodeOuput" and \meta{Immediate execution}. A "\par" is added after
"\CodeInput" if and only if the "\end" statement appears on its own
line. Here's an illustration:

\begin{sidebyside}
\NewExample{myex}{\ttfamily#}{#}{}
\parindent0pt

\begin{myex}
\TeX
\end{myex}
+\CodeInput+ yields +\CodeOutput+

\vskip1em
\begin{myex}
\TeX\end{myex}
+\CodeInput+ yields +\CodeOutput+
\end{sidebyside}

\noindent\llap{\textbullet\ }The "code" environment can be freely redefined as an
example environment.

\noindent\llap{\textbullet\ }All example environments obey "\TabSize" and "\Gobble"
as defined in the previous section, as well as "\LineNumber" if they are numbered
(see below). See the description of "\eTeXOff" and "\eTeXOn" below for a comment
on "\Gobble".

\meta{Options} may be one or several of the following (separated by commas):

\noindent\textcolor{\maccolor}{\texttt{numbered}}\par
\noindent Each line of "\CodeInput" is numbered. The count starts back to 1 at
each occurrence of the environment.

\noindent\textcolor{\maccolor}{\texttt{continuous}}\par
\noindent Each line of "\CodeInput" is numbered. The count starts where the
last occurrence of the same environment left. As an (utterly boring) example:\nobreak

\trycolorfalse\let\incolor\yellowcolor \let\outcolor\bluecolor \let\filcolor\redcolor
\begin{sidebyside}
\NewExample[numbered]{myex1}{\ttfamily#}¨  {}{\CodeInput}
\LineNumber{myex1}{\itshape}{1em}
\NewExample[continuous]{myex2}{\ttfamily¨  \color{red}#}{}{\CodeInput}
\LineNumber{myex2}{\itshape}{2em}
\begin{myex2}
First line
Second line
\end{myex2}
\begin{myex1}
First line
Second line
\end{myex1}
\begin{myex2}
Third line
Fourth line
\end{myex2}
\end{sidebyside}

\noindent\textcolor{\maccolor}{\texttt{visibleEOL}}\label{visibleEOL}\par\nobreak
\noindent This is more complicated and requires some knowledge of how \CD\
builds examples.

Although you might not know it, your \TeX\ distribution is very probably running
on \eTeX. That's the reason why \CD\ can process some code verbatim
and executes it at the same time, as in the example environments, without the need
for an external file. This is completely impossible with the original implementation of \TeX.
If, for some reason, you don't have \eTeX, or you're not running on it,
then \CD\ will use an external file.

However, \eTeX's `virtual external file' mechanism is not perfect, and
\CD\ has to cope with it. What happens is that when you use "\CodeOutput", \CD\
hacks your code a little in order to simulate a real \TeX\ code; namely, before
anything is processed, \CD\ removes ends of lines and commented parts of lines.
For instance, if you say:

\csize2cm
\begin{ex0}
\def\foo{%
  FOO!}
\foo
\end{ex0}

\noindent what \CD\ really processes with "\CodeInput" is \verb*"\def\foo{FOO!} \foo".
Most of the time, that's exactly what you want. But it might happen that you're
toying around with ends of lines or comment characters, and in that case everything
will go wrong, as in:

\csize4cm
\begin{ex0}
\catcode`\%=12
I'm writing a % sign.
\end{ex0}

\noindent This\cox(290,-1.8cm,.5cm,\hskip-1.2cm*\emph{SIGH}*) will \emph{not} produce `I'm writing a \% sign', because \CD\ will remove
everything from the comment sign to the end of the line, so that what "\CodeOuput"
will try to execute is:

\csize2.5cm
\begin{ex0}
\catcode`\
I'm writing a
\end{ex0}

\noindent and of course the aborted "\catcode" declaration will yield an error message.
To avoid this problem, the "visibleEOL" option makes \CD\ keeps everything. But now
there's another issue: comments and end of line characters are processed at the same
time as other macros and aren't interpreted independantly as in normal \TeX.
For instance, the following code, if the "visibleEOL" option is on for the environment
in question, will apply "\emph" to the end of line character and not to "A".

\csize1.5cm
\begin{ex0}
\emph
A
\end{ex0}

\noindent So you should be sure that comments and line ends occur where they won't hinder anything.
If you find this utterly complicated, then you can use an external file whenever you're
hacking ends of line, thanks to the following two macros.

\macrotopskip
\DescribeMacro{\eTeXOff}
\DescribeMacro{\eTeXOn}
\noindent The former makes \CD\ process all examples environments with an external file
(whose extension is~".exp").
The latter makes everything back to normal. If "\eTeXOff" applies, the "visibleEOL" option
is of course irrelevant. Note that these two macros apply to examples that follow them
and not to example definitions. For instance, "\eTeXOff" and then "\NewExample{myex}{#}{}{}"
will not lead \CD\ to use an external file whenever "myex" is called, but simply as long
as no "\eTeXOn" appears. To put simply, these two macros have no effect on "\NewExample".

If "\Gobble" is positive, examples with \eTeX\ and examples without behave differently.
The latter gobble characters before writing to the external file. Thus, "\CodeOutput"
will execute line with the first characters gobbled. With \eTeX, however, nothing
is gobbled in "\CodeOutput". This means that first characters, if meant to be
gobbled, will be executed. Most of the time, such characters are spaces,
and the difference won't be noticed. If, for some reason, you use other
characters instead, and if you want to call "\CodeOutput" nonetheless, then
a switch to an external file may be a good idea.





\subsection{\texttt{\bslash ShortVerb} and friends}

\CD\ provides a number of facilities to act on verbatim contexts. They
declare one or more character(s) to have a special effect under certain
circumstances. 

\macrotopskip
\DescribeMacro{\ShortVerb\marg{Character}}
\DescribeMacro\UndoShortVerb
\noindent This is well-known. \meta{Character} is turned into a shorthand
for "\verb". You can define only one such character, and that's why "\UndoShortVerb"
doesn't take an argument (like all "\Undo..." below). In \CD\ verbatim contexts, this character returns
to its normal value.

\UndoShortVerb
\begin{sidebyside}
\ShortVerb{*}
The command *\TeX* gives \TeX.

\begin{example}
And the star appeared:*
\end{example}\CodeInput
\end{sidebyside}
\ShortVerb"

\DescribeMacro{\ShortCode\oarg{Example name}\marg{Character}}
\DescribeMacro\UndoShortCode
\noindent This turns \meta{Character} into an equivalent of "\begin{code}"
and "\end{code}". In normal mode, the verbatim material will be printed
according to \meta{Example name}'s specifications. If this optional
argument is not present, then "\ShortCode" will follow "code"'s style.
Most importantly, in produce mode everything between two \meta{Characters}
will be written to the file under production.

\begin{sidebyside}
\RenewExample[continuous]{code}¨{\itshape\ttfamily#}{}{\CodeInput}
\LineNumber{code}{\small\rmfamily}{1em}
\ShortCode+ §cdcomment¤Oh yeah, braces are never£
            §cdcomment¤needed...£ 

\begin{code}
Here it's +normal+
\end{code}

+
Here it writes code...
+
\end{sidebyside}

"\ShortVerb" and "\ShortCode" have one caveat. If you "\Undo..."
them and the next character (disregarding spaces, comments and
ends of lines) is a short verb or a short code respectively,
in produce mode it will fire as if it was still active. A pair
of braces after the "\Undo..." statement prevents this.

\macrotopskip
\DescribeMacro{\VerbBreak\marg{Character}}
\DescribeMacro\UndoVerbBreak
\noindent Every once in a while, breaking a verbatim line may be
useful. In verbatim contexts, \meta{Character} breaks the line,
creates an unnumbered new one and indents it to the indentation of
the original line. When "\CodeOutput" is processed, the "\VerbBreak"
character is ignored. However, you should not break in the middle of
a control sequence (admittingly a strange idea), or it won't form.
It is also ignored, of course, when writing to a file in produce mode.

\UndoVerbBreak
\begin{sidebyside}
\VerbBreak{\=} §cdcomment¤An escape character is ok£
\begin{example*}
\TeX
  \emph=\TeX
\end{example*}\CodeInput

And the result is: \CodeOutput
\end{sidebyside}
\VerbBreak¨

\DescribeMacro{\VerbCommand\marg{Escape}\marg{Left brace}\marg{Right brace}}
\DescribeMacro\UndoVerbCommand
\noindent In verbatim contexts, those three characters will serve to form control sequences.
In "\CodeOuput" and produce mode, they are ignored. More specifically, \meta{Escape}
gobbles all letters following it (forming a putative command name) while everything
vanishes that appears between \meta{Left brace} and \meta{Right brace}. This is 
not a very sound device, and above all you should add a \meta{Left brace}-\meta{Right brace}
pair after a command called with \meta{Escape}, if it precedes a command to be executed
in "\CodeOutput". That is, suppose "\VerbCommand{!}{(}{)}", then "!foo\foo" is a very
bad idea in your code, \cox[6pt](70,3cm,0pt,Mind my word,\\don't use it)while "!foo()\foo" is ok.
All the comments in the examples here are done with "\VerbCommand".

Since numbered examples environment define the current label to be the number
of the current line, an interesting application is to use "\label" to refer to it.




\UndoVerbCommand
\begin{sidebyside}
\VerbCommand!()

(Everything is normal here!)
\RenewExample[numbered]{example}¨{\ttfamily#}{#}{}
\LineNumber{example}{}{1cm}

\begin{example}
\TeX !underline(\Tex!TeX)
%Second line !label(myline)
\end{example}

\CodeInput

gives \CodeOutput and the label is ¨on line \ref{myline}.
\end{sidebyside}
\VerbCommand§¤£


\DescribeMacro{\CodeEscape\marg{Character}}\label{CodeEscape}
\DescribeMacro\UndoCodeEscape
In normal mode, this command does absolutely nothing. However, in produce
mode, \meta{Character} becomes an escape character to form control sequences
that will be expanded when writing to the file under production. It's useful
mainly to put the values defined by "\ProduceFile" somewhere in your file. For
instance, the following code

\trycolorfalse\let\incolor\redcolor
\csize15cm
\begin{ex0}
\CodeEscape!
\ProduceFile{mypack.sty}[mypack][v.2.1][2009/02/24]

\begin{code}
\ProvidesPackage{!FileName}[!FileDate!space !FileVersion!space My super package.]
\end{code}
\end{ex0}

\noindent\cox(210,14cm,3.5cm,invisible...) will write "\ProvidesPackage{mypack}[2009/02/24 v.2.1 My super package.]"
to "mypack.sty".


\subsection{Using \textsf{fancyvrb}}
\CD\ is minimally compatible with \textsf{fancyvrb}, in the sense that
verbatim characters defined and undefined with "\DefineShortVerb"
and "\UndefineShortVerb" are recognized in produce mode (hopefully). Besides, verbatim environments
defined with "\DefineVerbatimEnvironment" are automatically added to the list
of dangerous environments. The environments offered by \textsf{fancyvrb} and
the \textsf{fvrb-ex} companion package already belong to that list.

You can even redefine the "code" environment with \textsf{fancyvrb} facilities.\footnote{%
It will indeed add \texttt{code} to the list of dangerous environment, which is already
the case when \texttt{code} is redefined with \texttt{$\backslash$RenewExample}. But \CD\ evaluates
whether an environment is \texttt{code} before checking the list of dangerous environments.}
However:

\noindent\llap{\textbullet\ }"\ShortCode" will stick to the last style defined
for "code" (if it is set to follow this environment).

\noindent\llap{\textbullet\ }Since everything is gobbled after "\begin{code}"
in produce mode, you can freely put your \textsf{keyval} pairs here, as usual
with \textsf{fancyvrb}. However, \emph{you should not input these pairs on
the following line(s)}, although it's ok with \textsf{fancyvrb}. The following
code will lead "xleftmargin=1cm]" to be written on the file under production.


\csize5cm
\begin{ex0}
\begin{code}[frame=single,
xleftmargin=1cm]
\def\foo{FOO}
\end{code}
\end{ex0}

\noindent\llap{\textbullet\ }The "gobble" and "commandchars" parameters will
be obeyed in normal mode (since \textsf{fancyvrb} is in charge), but \emph{not
in produce mode, unless you also specify the} "\Gobble" \emph{and}
"\VerbCommand" \emph{parameters (see above) accordingly}.



\section{Summary of commands}

In this section I explain the behavior of all \CD\ constructions in normal and
produce mode respectively. Commands which have some effect in produce mode are
subject to the restrictions given in section~\ref{dangerous}.

\newcommand\NM{\textbf{Normal Mode: }}
\newcommand\PM{\par\noindent\bgroup\def\par{\egroup\endgraf}\itshape\textbf{Produce Mode: }}
\newcommand\NMX{\textbf{Normal Mode: }Does nothing.\par}
\newcommand\PMX{\par\noindent\textit{\textbf{Produce Mode: }Does nothing.}\par}
\let\PrintMacro\OneMac\let\macrotopskip\relax
\small

\subsection{Class options}

\PrintMacro{autoclose}
\NMX
\PM The current file is closed when a new one is opened with "\ProduceFile".

\PrintMacro{index}
\NM Loads \textsf{makeidx} and calls "\makeindex". "\StopHere" automatically
launches "\printindex".
\PMX

\PrintMacro{noheader}
\NMX
\PM No header is written to the file when it is opened.

\PrintMacro{obeystop}
\NM The document stops at "\StopHere"\marg{Code} and executes
\meta{Code}. If the "index" option is on, "\printindex" is
executed after \meta{Code}.
\PMX

\PrintMacro{tracing0, tracing1, tracing2}
\NMX
\PM \CD\ normally writes a report to the log file. If "tracing0"
is on, there's no report; if "tracing1" is on (which is default),
\CD\ reports only about opening files and writing code. With
"tracing2", it also reports about characters defined as 
"\ShortVerb" or "\CodeEscape", environments added to the
list of dangerous environments, etc.

\subsection{Environments}


\DescribeEnvironment{code}
\NM The content is displayed verbatim according to the style
defined for "code".
\PM The content is written to the file in production.

\DescribeEnvironment{example}
\NM A minimal example environment that provides "\CodeInput"
(in typewriter font) and "\CodeInput".
\PM The content is skipped.

\DescribeEnvironment{invisible}
\NM The content is skipped.
\PM The content is written to the file in production.

\subsection{Commands}

\DescribeMacro\AddBlankLine
\NMX
\PM Adds a blank line to the file in production.

\DescribeMacro\bslash
\NM Prints \bslash. Designed to adapt to \textsf{hyperref}'s bookmarks.
\PMX

\DescribeMacro{\BoxTolerance\marg{Dimension}}
\NM Excess size tolerated before a verbatim line is
reported as an overfull box.
\PMX

\DescribeMacro{\CloseFile\marg{File}}
\NM "\FileName" and others are not available anymore.
\PM Closes \meta{File}. No file is considered in
production until the next "\ProduceFile", even if
there are open files. Useless in "autoclose" mode.

\DescribeMacro{\CodeEscape\marg{Character}}
\NMX
\PM \meta{Character} turns into an escape character in
"code" contexts.

\DescribeMacro{\CodeFont\marg{Font specifications}}
\NM The style of the "code" environment if it has not
been redefined with "\RenewExample". Default is
"\ttfamily".
\PMX

\DescribeMacro\CodeInput
\NM Displays the code of the last example environment
verbatim, according to the style defined for that
environment.
\PMX

\DescribeMacro\CodeOutput
\NM Executes the code of the last example environment,
according to the style defined for that environment.
\PMX

\DescribeMacro{\DangerousEnvironment\marg{List of environments}}
\NMX
\PM The environments in the list are skipped during processing.

\DescribeMacro{\DefineEnvironment\marg{Environment}}
\NM Prints \meta{Environment} according to "\PrintMacro" and adds
it to the index with `(environment)' and a line number typeset
according to "\DefineIndexFont".
\PM Gobbles the first characters of \meta{Environment}, just in case.

\DescribeMacro{\DefineIndexFont\marg{Font specifications}}
\NM Style of the page number in the index for "\DefineMacro"
and "\DefineEnvironment" entries.
\PMX

\DescribeMacro{\DefineMacro\marg{Macro}}
\NM Prints \meta{Macro} according to "\PrintMacro" and adds
it to the index with a line number typeset according to "\DefineIndexFont".
\PM Gobbles the first characters of \meta{Macro}, just in case.

\DescribeMacro{\DescribeEnvironment\marg{Environment}}
\NM Prints \meta{Environment} according to "\PrintMacro" and adds
it to the index with `(environment)' and a line number typeset
according to "\DescribeIndexFont".
\PM Gobbles the first characters of \meta{Environment}, just in case.

\DescribeMacro{\DescribeIndexFont\marg{Font specifications}}
\NM Style of the page number in the index for "\DescribeMacro"
and "\DescribeEnvironment" entries.
\PMX

\DescribeMacro{\DescribeMacro\marg{Macro}}
\NM Prints \meta{Macro} according to "\PrintMacro" and adds
it to the index with a line number typeset according to "\DescribeIndexFont".
\PM Gobbles the first characters of \meta{Macro}, just in case.

\DescribeMacro\DocStripMarginpar
\NM Sets the adequate values for the proper printing of macros
with "\DescribeMacro" and "\DefineMacro" (and variants for environments),
so that they appear "\marginpar"'ed as with \textsf{DocStrip}.
More precisely, it executes "\reversmarginpar", and sets "\marginparpush"
to "0pt" and "\marginparwidth" to "8pc".
\PMX

\DescribeMacro\eTeXOff
\NM All subsequent example environments are processed with an
external file, whose extension is~".exp".
\PMX

\DescribeMacro\eTeXOn
\NM All subsequent example environments are processed without an
external file. This is default. (Requires \eTeX, of course.)
\PMX

\DescribeMacro{\Gobble\marg{Number}}
\NM The number of characters that will be gobbled at the beginning
of each example and code environments. In case of a blank line, nothing
is gobbled, but a blank line is added. Tab characters count as one character.
\PM Same as in normal mode, but when writing to the file in production.

\DescribeMacro{\Header\marg{Text}}
\NMX
\PM Text to be written at the beginning of a file when it is opened
with "\ProduceFile". Comment characters will be automatically added
at the beginning of each line. Ends of lines are obeyed. If the "noheader"
option is on, nothing is written.

\DescribeMacro{\IgnorePrefix\marg{Macro prefix}}
\NM Ignores \meta{Macro prefix} when sorting index entries generated
by "\DescribeMacro" and "\DefineMacro". \meta{Macro prefix} will be
typeset according to "\PrintPrefix" in the index.
\PMX

\DescribeMacro{\LineNumber\marg{Name}\marg{Font specifications}\marg{Width}\oarg{Number}}
\NM The line number of \meta{Name} will be typeset according to
\meta{Font specifications} in a box that will spread from the left\cox(270,-4.5cm,12pt,What???)
margin into the main text width by a length of \meta{Width} (0pt by default).
The next \meta{Name} will start at \meta{Number} if specified.
\PMX

\DescribeMacro{\marg\marg{Argument}}
\NM "\marg{Argument}" prints \marg{Argument} (mandatory argument).
\PMX

\DescribeMacro{\meta\marg{Argument}}
\NM "\meta{Argument}" prints \meta{Argument}.
\PMX

\DescribeMacro{\NewExample\oarg{Options}\marg{Name}\marg{Code input}\marg{Code output}\marg{Immediate execution}}
\NM Creates \meta{Name} as an example environment to provide
"\CodeInput" as \meta{Code input} (where the code to be typeset
is represented by "#") and "\CodeOutput" as \meta{Code output}
(where the code to be executed is represented by "#"). When
encountered, \meta{Name} executes \meta{Immediate execution}.
\meta{Code input}, \meta{Code output} and \meta{Immediate execution}
can be empty.\\
Options are:\\
\texttt{numbered:} Each line of \meta{Name} is numbered.\\
\texttt{continuous:} Each line of \meta{Name} is numbered and numbering
continues from one \meta{Name} to the other.\\
\texttt{visibleEOL:} If \meta{Name} is processed with \eTeX,
This prevents ends of lines and commented parts of lines from being removed
before anything is executed in "\CodeInput". See page \pageref{visibleEOL}
for a discussion.
\PM Adds \meta{Name} to the list of dangerous environments and gobbles
the remaining arguments.

\DescribeMacro{\oarg\marg{Argument}}
\NM "\oarg{Argument}" prints \oarg{Argument} (optional argument).
\PMX

\DescribeMacro{\parg\marg{Argument}}
\NM "\parg{Argument}" prints \parg{Argument} (picture argument).
\PMX

\DescribeMacro{\PrintMacro\marg{Macro or environment}}
\NM Typesets the argument to "\DescribeMacro", "\DefineMacro",
"\DescribeEnvironment" and "\Defi§-neEnvironment". Should be freely
redefined by users. By default, it prints its argument as with
\textsf{DocStrip}, provided "\DocStripMarginpar" has been executed
beforehand.
\PMX

\DescribeMacro{\PrintPrefix\marg{Macro prefix}}
\NM Typesets \meta{Macro prefix}, as defined by "\IgnorePrefix",
in the index.
Should be redefined by the user. By default, it does nothing.
\PMX

\DescribeMacro{\ProduceFile\marg{File}\oarg{File name}\oarg{File version}\oarg{File date}}
\NM Provides \meta{File} as "\FileSource", \meta{File name} as "\FileName",
\meta{File version} as "\FileVersion" and \meta{File date} as "\FileDate".
\PM Opens \meta{File} and writes the header (unless "noheader" is on),
unless \meta{File} is already open and "autoclose" is not specified, in
which case \CD\ will simply puts \meta{File} back in production. Subsequent code
will be written to this file. Closes the current file if "autoclose" is on.
Provides \meta{File name} as "\FileName",
\meta{File version} as "\FileVersion" and \meta{File date} as "\FileDate",
to be used with "\CodeEscape".

\DescribeMacro{\RenewExample\oarg{Options}\marg{Name}\marg{Code input}\marg{Code output}\marg{Immediate execution}}
\NM Same as "\NewExample" to redefine \meta{Name}.
\PM Adds \meta{Name} to the list of dangerous environments and gobbles
the remaining arguments.

\DescribeMacro{\ShortCode\marg{Character}}
\NM Turns \meta{Character} into a shorthand for "\begin{document}"
and "\end{document}".
\PM Like in normal mode: everything between two \meta{Characters}
will be written to the file in production.

\DescribeMacro{\ShortVerb\marg{Character}}
\NM Turns \meta{Character} into a shorthand for "\verb".
\PM Subsequently gobbles everything between two \meta{Characters}.

\DescribeMacro\StartIgnore
\NMX
\PM Stops executing anything until "\StopIgnore".

\DescribeMacro{\StopHere\marg{Code}}
\NM If the "obeystop" option is on, executes
\meta{Code} followed by "\printindex" if "index" is on, and
ends the document.
\PMX

\DescribeMacro\StopIgnore
\NMX
\PM Marks the end of "\StartIgnore".

\DescribeMacro{\TabSize\marg{Number}}
\NM Sets the number of spaces to represent a tab character
in verbatim contexts.
\PMX

\DescribeMacro\UndoCodeEscape
\NMX
\PM Sets the "\CodeEscape" character to a normal character.

\DescribeMacro\UndoShortCode
\NM Sets the "\ShortCode" character to a normal character.
\PM Sets the "\ShortCode" character to a normal character.

\DescribeMacro\UndoShortVerb
\NM Sets the "\ShortVerb" character to a normal character.
\PM Sets the "\ShortVerb" character to a normal character.

\DescribeMacro\UndoVerbBreak
\NM Sets the "\VerbBreak" character to a normal character.
\PM Sets the "\VerbBreak" character to a normal character.

\DescribeMacro\UndoVerbCommand
\NM Sets the "\VerbCommand" characters to normal characters.
\PM Sets the "\VerbCommand" character to normal characters.

\DescribeMacro{\VerbBreak\marg{Character}}
\NM Turns \meta{Character} into a line breaker in verbatim
contexts; more precisely, the line will break where \meta{Character}
appears and will be indented with the same amount of space as the
original one. \meta{Character} is ignored in "\CodeOutput".
\PM Ignores \meta{Character} when writing to the file in production.

\DescribeMacro{\VerbCommand\marg{Escape}\marg{Left brace}\marg{Right brace}}
\NM Turns \meta{Escape} into an escape character in verbatim contexts,
and \meta{Left brace} and \meta{Right brace} into characters of category
1 and 2 respectively. In "\CodeOutput", \meta{Escape} gobbles all subsequent
letters and everything between \meta{Left brace} and \meta{Right brace}
is gobbled too.
\PM Does the same as normal mode for "\CodeOutput". Letters following
\meta{Escape} are gobbled, as is everything between \meta{Left brace}
and \meta{Right brace}.

\normalsize
\StopHere{%
\def\section*#1{\part{#1}
\itshape
This index was generated by the \emph{\texttt{\bslash DescribeMacro}}-like
commands. It only reports where macros are described (page numbers in
normal font) and defined (page numbers in italics).
In the current version, \CD\ does not index macros when used in the code.

Entries are sorted ignoring the \emph{\texttt{cd@}} and \emph{\texttt{cd@@}} prefixes.\vskip1em}%
\catcode`\Z=0\relax%
\let\partname\relax%
\let\thepart\relax}

\part{Implementation}
\newskip\codeskip
\newskip\printskip
\codeskip=2cm
\newskip\boxskip
\boxskip=2cm
\RenewExample[continuous]{code}%
	{\let\noindent\relax\color{\maccolor}\ttfamily\small#}{}%
	{\par\leftskip\codeskip\vskip.5em\CodeInput\vskip.5em\goodbreak}
\LineNumber{code}{\footnotesize\rmfamily}{0pt}[1]
\DocStripMarginpar
\def\PrintMacro#1{%
	\noindent%
	\marginpar{%
		\raggedleft\strut\ttfamily\small\hbox to\boxskip{%
			\printskip\codeskip%
			\advance\printskip1.6cm%
			\hbox to\printskip{\hfil#1}\hss}}\ignorespaces}
\everypar{\hangindent\codeskip\hangafter0\relax}
\ShortCode/
\BoxTolerance{10cm}
\let\Section\section
\let\Subsection\subsection
\let\Subsubsection\subsubsection
\def\section#1{\Section{#1}\everypar{\hangindent\codeskip\hangafter0\relax}\noindent\ignorespaces}
\def\subsection#1{\Subsection{#1}\everypar{\hangindent\codeskip\hangafter0\relax}\noindent\ignorespaces}
\def\subsubsection#1{\Subsubsection{#1}\everypar{\hangindent\codeskip\hangafter0\relax}\noindent\ignorespaces}

\noindent The usual things (";" is my "\CodeEscape" character). Turning "^^?" into
an active character is less usual but useful to delimit ends of code material.
\CodeEscape;



/
\NeedsTeXFormat{LaTeX2e}
\ProvidesClass{;FileName}[;FileDate ;FileVersion Code and documentation in one file.]
\makeatletter
\catcode`\^^?=13
/\AddBlankLine
\UndoCodeEscape


\section{Options and basic definitions}
\DefineMacro\cd@GetClass
Options are mostly conditional switching. "\cd@tracingmode" will
be used in an "\ifcase" statement. "\cd@GetClass" will be analyzed
to retrieve the class and its options.


/
\newif\ifcd@produce
\newif\ifcd@autoclose
\newif\ifcd@obeystop
\newif\ifcd@makeindex
\newif\ifcd@noheader
\newcount\cd@tracingmode
\cd@tracingmode1
\def\cd@GetClass{article()}

\DeclareOption{autoclose}{\cd@autoclosetrue}
\DeclareOption{produce}{\cd@producetrue}
\DeclareOption{index}{\cd@makeindextrue}
\DeclareOption{obeystop}{\cd@obeystoptrue}
\DeclareOption{noheader}{\cd@noheadertrue}
\DeclareOption{tracing0}{\cd@tracingmode0}
\DeclareOption{tracing1}{\cd@tracingmode1}
\DeclareOption{tracing2}{\cd@tracingmode2}
\DeclareOption*{\edef\cd@GetClass{\CurrentOption()}}
\ProcessOptions\relax
/\AddBlankLine



\DefineMacro\cd@end
\DefineMacro\cd@LoadClass
\DefineMacro\cd@GetOptions
We define "\cd@LoadClass" as a recursive retrieval of options,
then passed to the class with "\PassOptionsToClass", which we load.
This is done only if we're not in produce mode, in which case no
class is loaded.
/
\def\cd@end{cd@end}
\ifcd@produce
\else
\def\cd@LoadClass#1(#2){%
	\def\cd@Class{#1}
	\expandafter\cd@GetOptions#2;cd@end;%
	\LoadClass{#1}%
	\@ifnextchar({\expandafter\@gobble\@gobble}{}}
\def\cd@GetOptions#1;{%
	\def\cd@TempArg{#1}
	\ifx\cd@TempArg\cd@end%
		\let\cd@next\relax
	\else%
		\PassOptionsToClass{#1}{\cd@Class}%
		\let\cd@next\cd@GetOptions%
	\fi\cd@next}
\expandafter\cd@LoadClass\cd@GetClass
/\AddBlankLine

\DefineMacro\StopHere
Still in normal mode, we load \textsf{makeidx} if required
and define "\StopHere" accordingly.
/
\ifcd@makeindex
	\RequirePackage{makeidx}
	\makeindex
\else
	\let\printindex\relax
\fi
\ifcd@obeystop
	\ifcd@makeindex
		\long\def\StopHere#1{#1\relax\par\printindex\end{document}}
	\else
		\long\def\StopHere#1{#1\relax\par\end{document}}
	\fi
\else
	\long\def\StopHere#1{}
\fi
\fi
/\AddBlankLine

\section{Normal mode}
Although the following code is used in normal mode only,
I did not feel like embedding hundreds of lines under a "\ifcd@produce"
conditional. Pure superstition, perhaps.

Here's the switch for \eTeX\ and some shorthands.
/
\newif\ifcd@eTeX
\@ifundefined{eTeXversion}{\cd@eTeXfalse}{\cd@eTeXtrue}

\def\cd@Warning{\ClassWarningNoLine{codedoc}}
\def\cd@Error#1{\ClassError{codedoc}{#1}{}}
/\AddBlankLine

\subsection{Describing macros}

\DefineMacro\DocStripMarginpar
\DefineMacro\PrintMacro
Most of the following macros are imitated from \textsf{DocStrip},
in a simpler but less careful manner. The first two are straightforward.
/
\def\DocStripMarginpar{\reversemarginpar\marginparpush0pt\relax\marginparwidth8pc\relax}
\def\PrintMacro#1{\noindent\marginpar{\raggedleft\strut\ttfamily#1}\ignorespaces}
/\AddBlankLine

\DefineMacro\DescribeIndexFont
\DefineMacro\DescribeMacro
\DefineMacro\cd@DescribeMacro
\DefineMacro\DescribeEnvironment
\DefineMacro\cd@DescribeEnvironment

\DefineMacro\DefineIndexFont
\DefineMacro\DefineMacro
\DefineMacro\cd@DefineMacro
\DefineMacro\DefineEnvironment
\DefineMacro\cd@DefineEnvironment
\vskip-24pt\noindent"\DescribeMacro" and its companions first turn "@" into a letter,
so that a control sequence containing it is recognized as such,
sets "\cd@Index", used in the "\ifcase" statement below (a simple
conditional could do the job, since there are only two values,
but there might be more someday if one wants to distinguish
other index entries, like `used' macros), and pass their
arguments to "\PrintMacro" with the first token "\string"'ed
(even in the case of an environment, because someone might
describe its environment with a "\begin{myenv}" command).
In case of a macro, the argument is also passed to "\cd@MakeEntry"
to index it.

The \textsf{hyperref} package does not work properly with indexes
if a style is specified with "|" in the entry. Since we use such
styles, and since we want to use \textsf{hyperref}, we circumvent
the problem with "\hyperpage" added to the style. By default, it
does nothing, but if the user loads \textsf{hyperref}, it will
have the adequate meaning.
/
\newcount\cd@Index
\def\hyperpage#1{#1}

\def\DescribeIndexFont#1{\gdef\cdatDescribeFont##1{{#1\hyperpage{##1}}}}
\DescribeIndexFont{}
\def\DescribeMacro{\makeatletter\cd@DescribeMacro}
\def\cd@DescribeMacro#1{%
	\makeatother%
	\cd@Index=0 %
	\cd@MakeEntry#1\cd@EndOfEntry%
	\PrintMacro{\string#1}}
\def\DescribeEnvironment{\makeatletter\cd@DescribeEnvironment}
\def\cd@DescribeEnvironment#1{%
	\makeatother%
	\index{#1@\texttt{#1} (environment)|cdatDescribeFont}%
	\PrintMacro{\string#1}}

\def\DefineIndexFont#1{\gdef\cdatDefineFont##1{{#1\hyperpage{##1}}}}
\DefineIndexFont{\itshape}
\def\DefineMacro{\makeatletter\cd@DefineMacro}
\def\cd@DefineMacro#1{%
	\makeatother%
	\cd@Index1 %
	\cd@MakeEntry#1\cd@EndOfEntry%
	\PrintMacro{\string#1}}
\def\DefineEnvironment{\makeatletter\cd@DefineEnvironment}
\def\DefineEnvironment#1{%
	\makeatother%
	\index{#1@\texttt{#1} (environment)|cdatDefineFont}%
	\PrintMacro{\string#1}}
/\AddBlankLine

\DefineMacro\cd@MakeEntry
This takes two arguments but considers only the first one,
so that "\DescribeMacro{\foo\marg{Argument}}" will
ignore "\marg{Argument}". We pass that argument to "\cd@AnalyzeEntry"
with the escape character removed (for a proper indexing),
call "\cd@AnalyzePrefix" on the result and finally "\cd@@MakeEntry"
/
\def\cd@MakeEntry#1#2\cd@EndOfEntry{%
	\def\cd@TempEntry{}%
	\begingroup\escapechar\m@ne\expandafter\cd@AnalyzeEntry\string#1\cd@end\endgroup%
	\expandafter\cd@AnalyzePrefix\cd@TempEntry\cd@end%
	\expandafter\cd@@MakeEntry\cd@TempEntry\cd@EndOfEntry}/

\DefineMacro\cd@AnalyzeEntry
\DefineMacro\AtChar
The aim of this macro is to process "@". Indeed, "@"
is \textsf{MakeIndex}'s operator to signal that an entry
should be indexed under another name (as done here). But
"@" is also a very popular letter in \TeX's world when it
comes to macros. \textsf{DocStrip}'s solution is to create
a special style file for \textsf{MakeIndex}, so that the
function of "@" is taken over by another character. But
then, when a user compiles a \textsf{DocStrip} document,
this style file must be indicated to \textsf{MakeIndex},
which many people might not do. So I prefer to leave
\textsf{MakeIndex} alone and process the entry beforehand,
replacing "@" by a character denotation. That's the job
of "\cd@AnalyzeEntry", which scans the macro name token
by token and replace "@" by "\AtChar".
/
\chardef\AtChar=`\@
\def\cd@AnalyzeEntry#1{%
	\let\cd@next\cd@AnalyzeEntry%
	\ifx#1\cd@end%
		\let\cd@next\relax%
	\else\if#1@%
		\expandafter\gdef\expandafter\cd@TempEntry\expandafter{\cd@TempEntry\AtChar}%
	\else%
		\expandafter\gdef\expandafter\cd@TempEntry\expandafter{\cd@TempEntry#1}%
	\fi\fi\cd@next}
/\AddBlankLine

\DefineMacro\IgnorePrefix
Here comes the mechanism to remove prefixes when sorting entries.
"\IgnorePrefix" simply resets%
\cox[1pt](0,-3.7cm,8pt,\hskip-.4cm\raise3pt\hbox{{\normalsize\ttfamily\bslash}\hskip.5cmI am a macro})
some values and call "\cd@IgnorePrefix" on its argument along with a terminator.
/
\newcount\cd@PrefixCount
\def\IgnorePrefix#1{\cd@PrefixCount\z@\def\Prefix{}\cd@IgnorePrefix#1\cd@end}
/

\DefineMacro\cd@IgnorePrefix
\DefineMacro\cd@MakePrefix
This analyzes the prefix just like "\cd@AnalyzeEntry" above and
replaces all occurrences of "@" by "\AtChar". Since the name
of the macro is "\string"'ed when subjected to "\DefineMacro"
and others, we also "\string" all letters of the prefix, which have then
category code 12. 
/
\def\cd@IgnorePrefix#1{%
	\let\cd@next\cd@IgnorePrefix%
	\ifx#1\cd@end%
		\def\cd@next{\expandafter\cd@ScanPrefix\Prefix\cd@end}%
	\else\if#1@%
		\expandafter\def\expandafter\Prefix\expandafter{\Prefix\AtChar}%
	\else%
		\edef\cd@PrefixLetter{\string#1}%
		\expandafter\cd@MakePrefix\cd@PrefixLetter%
	\fi\fi\cd@next}
\def\cd@MakePrefix#1{%
	\expandafter\def\expandafter\Prefix\expandafter{\Prefix#1}}%
/

\DefineMacro\cd@ScanPrefix
\DefineMacro\cd@DefPrefix
\DefineMacro\cd@AnalyzePrefix
Then we just scan the prefix to compute the number of
characters it is made of. "\cd@Analy§-zePrefix" is defined
accordingly to take the right number of characters out of 
a macro name (fed in "\cd@MakeEntry" above) and
lump them into "\cd@TempPrefix", and define the rest of the
entry as the remaining characters up to the terminator.
/
\def\cd@ScanPrefix#1{%
	\ifx#1\cd@end%
		\let\cd@next\cd@DefPrefix%
	\else%
		\advance\cd@PrefixCount\@ne%
		\let\cd@next\cd@ScanPrefix%
	\fi\cd@next}
\def\cd@DefPrefix{%
	\ifcase\cd@PrefixCount%
		\def\cd@AnalyzePrefix##1\cd@end{}%
	\or\def\cd@AnalyzePrefix##1##2\cd@end{%
		\def\cd@TempPrefix{##1}\def\cd@RestOfEntry{##2}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3\cd@end{%
		\def\cd@TempPrefix{##1##2}\def\cd@RestOfEntry{##3}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3##4\cd@end{%
		\def\cd@TempPrefix{##1##2##3}\def\cd@RestOfEntry{##4}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3##4##5\cd@end{%
		\def\cd@TempPrefix{##1##2##3##4}\def\cd@RestOfEntry{##5}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3##4##5##6\cd@end{%
		\def\cd@TempPrefix{##1##2##3##4##5}\def\cd@RestOfEntry{##6}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3##4##5##6##7\cd@end{%
		\def\cd@TempPrefix{##1##2##3##4##5##6}\def\cd@RestOfEntry{##7}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3##4##5##6##7##8\cd@end{%
		\def\cd@TempPrefix{##1##2##3##4##5##6##7}\def\cd@RestOfEntry{##8}\cd@ComparePrefix}%
	\or\def\cd@AnalyzePrefix##1##2##3##4##5##6##7##8##9\cd@end{%
		\def\cd@TempPrefix{##1##2##3##4##5##6##7##8}\def\cd@RestOfEntry{##9}\cd@ComparePrefix}%
	\fi\ignorespaces}
/

\DefineMacro\cd@ComparePrefix
Comparing prefixes is simply a matter of string testing.
In case they match, the entry is redefined as the "\cd@RestOfEntry",
so that macros will be indexed with the prefix removed.
/
\newif\ifcd@Prefix
\def\cd@ComparePrefix{%
	\ifx\cd@TempPrefix\Prefix%
		\expandafter\def\expandafter\cd@TempEntry\expandafter{\cd@RestOfEntry}%
		\cd@Prefixtrue%
	\else%
		\cd@Prefixfalse%
	\fi}
/

\IgnorePrefix{cd@@}
\DefineMacro\cd@@MakeEntry
\IgnorePrefix{cd@}
\DefineMacro\PrintPrefix
Finally, "\cd@@MakeEntry" indexes the macro under its
name with a prefixed escapechar (since it was removed
above) and "\Prefix" in case it was found to match. We also
set some default values.
/
\def\cd@@MakeEntry#1\cd@EndOfEntry{%
	\ifcd@Prefix%
		\ifcase\cd@Index%
			\index{#1@\texttt{\char\escapechar\PrintPrefix\Prefix#1}|cdatDescribeFont}%
		\or%
			\index{#1@\texttt{\char\escapechar\PrintPrefix\Prefix#1}|cdatDefineFont}%
		\fi%
	\else%
	\ifcase\cd@Index%
			\index{#1@\texttt{\char\escapechar#1}|cdatDescribeFont}%
		\or%
			\index{#1@\texttt{\char\escapechar#1}|cdatDefineFont}%
		\fi%
	\fi}

\IgnorePrefix{}%
\let\PrintPrefix\relax
/\AddBlankLine

\DefineMacro\meta
\DefineMacro\marg
\DefineMacro\oarg
\DefineMacro\parg
These again are imitated from the \textsf{DocStrip} bundle,
with less care.
/
\def\meta#1{{\ensuremath\langle\emph{#1}\ensuremath\rangle}}
\def\marg#1{\texttt{\{}\meta{#1}\texttt{\}}}
\def\oarg#1{\texttt{[}\meta{#1}\texttt{]}}
\def\parg#1{\texttt{(}\meta{#1}\texttt{)}}
/

\DefineMacro\cd@bslash
\DefineMacro\bslash
We define our backslash to adapt to \textsf{hyperref}.
To this end, we use "\texorpdfstring", an \textsf{hyperref}
command that expands to its first argument in normal contexts
and to its second one in bookmarks.

The only problem is that \textsf{hyperref} defines
"\textorpdfstring" with "\newcommand" instead of "\def".
So we obviously can't define it here, and we wait for the
beginning of the document.
/
\def\cd@bslash{\char`\\}
\def\bslash{\texorpdfstring{\cd@bslash}{\string\\}}
\AtBeginDocument{\@ifundefined{texorpdfstring}{\def\texorpdfstring#1#2{#1}}{}}
/

\subsection{\texttt{\bslash ShortVerb} and associates}

\DefineMacro\cd@CharErr
\DefineMacro\cd@BadChar
Before entering the intricate realm of verbatim text, here are some
simpler definitions. First, we delimit what characters we consider to
be acceptable in "\ShortVerb" and other. The choice might seem rather
conservative, but things are less dangerous this way.

/
\def\cd@CharErr#1#2{%
	\bgroup
		\escapechar\m@ne
		\cd@Error{You can't use \string#1 for \string\\#2}
	\egroup}

\newif\ifcd@BadChar

\def\cd@BadChar#1#2{%
	\cd@BadChartrue
	\ifcase\catcode`#1 % \
		\cd@CharErr{\\}{#2}%
	\or% {
		\cd@CharErr{\{}{#2}%
	\or% }
		\cd@CharErr{\}}{#2}%
	\or% $
		\cd@BadCharfalse%
	\or% &
		\cd@BadCharfalse%
	\or% ^^M
	\or% #
		\cd@BadCharfalse%
	\or% ^
		\cd@BadCharfalse%
	\or% _
		\cd@BadCharfalse%
	\or% Ignored
	\or% Spaces
		\cd@CharErr{spaces}{#2}%
	\or% Letters
		\cd@CharErr{letters}{#2. \MessageBreak That's really bad}%
	\or% Other
		\cd@BadCharfalse%
	\or% Active
		\cd@CharErr{#1}{#2 - it's already active}%
	\or% %
		\cd@CharErr{#1}{#2}%
	\fi}
/\AddBlankLine

\DefineMacro\cd@UndoErr
\DefineMacro\cd@DefErr
We also define two templates for error messages in case
the user wants to "\Undo..." something that was never done
or define a new character while one is already in use.

/
\def\cd@UndoErr#1{%
	\bgroup%
		\escapechar\m@ne%
		\cd@Error{%
			There is no \string\\\string#1\space defined.\MessageBreak%
			\string\\Undo\string#1\space on line \the\inputlineno\space is useless}%
	\egroup}
\def\cd@DefErr#1#2{%
	\bgroup%
	\escapechar\m@ne%
		\expandafter\xdef\csname cd@#2Error\endcsname{%
			\noexpand\cd@Error{%
				You've already defined \string#1 as a \string\\#2\noexpand\MessageBreak%
				on l. \the\inputlineno. You can't have two.\noexpand\MessageBreak%
				Say \string\\Undo#2\space and then \string\\#2\space to change}}%
	\egroup}
/\AddBlankLine

\DefineMacro\ShortVerb
Before defining any character, we run some tests: is it a bad character,
and is there another character already in use? In the latter case, "\ifcd@ShortVerb"
should be switched to "true".
/
\newif\ifcd@ShortVerb

\def\ShortVerb#1{%
	\cd@BadChar{#1}{ShortVerb}%
	\ifcd@BadChar%
	\else\ifcd@ShortVerb
		\cd@ShortVerbError
/

\noindent If none of the above applies, we switch the conditional to
true define "\cd@ShortVerbError" with "\cd@DefErr". We also store
the character's original catcode to restore if undone.
/
	\else
		\cd@ShortVerbtrue
		\cd@DefErr{#1}{ShortVerb}
		\chardef\cd@ShortVerbCat\catcode`#1%
/

\noindent Then we use the "~" with lowercase trick to define
the character.
/
		\bgroup%
			\lccode`\~=`#1%
			\lowercase{%
/

\noindent A "\ShortVerb" character makes the adequate modifications
to display text verbatim. "\cd@Verbatim" is \CD's container of
all such modifications (mostly catcode changing). "\catcode`#1=13"
is necessary because the character might be one of the specials 
whose catcode is changed in "\cd@Verbatim", e.g. "&". We also
launch "\cd@ShortVerb" which works like "\verb".

"\leavevmode" is needed in case the "\ShortVerb" character
starts a paragraph, as in the one you're reading.
/
				\gdef~{\leavevmode\bgroup\ttfamily\cd@Verbatim\catcode`#1\active\cd@ShortVerb}%
				\gdef\cd@ShortVerb##1~{##1\egroup}%
/

\noindent Finally we (re)define "\UndoShortVerb" to restore the original catcode
and switch the appropriate conditional. Last but not least, we make the
character active.
/
				\gdef\UndoShortVerb{%
					\ifcd@ShortVerb%
						\cd@ShortVerbfalse%
						\catcode`~\cd@ShortVerbCat%
					\else%
						\cd@UndoErr{\ShortVerb}%
					\fi}}%
		\egroup%
		\catcode`#1=13
	\fi\fi}%
/

\DefineMacro\UndoShortVerb
This is the default definition for this command, when no
"\ShortVerb" has been defined.
/
\def\UndoShortVerb{\cd@UndoErr{\ShortVerb}}
/\AddBlankLine

\DefineMacro\ShortCode
"\ShortCode" works with the same pattern as "\ShortVerb"
with important variations. First, we check whether there's
an optional argument.
/
\newif\ifcd@ShortCode
\newif\ifcd@ShortCodeChar

\def\ShortCode{%
	\@ifnextchar[
		{\cd@MakeShortCode}
		{\cd@MakeShortCode[code]}}
/

\DefineMacro\cd@MakeShortCode
Then we define the real macro. We store the name of
the environment and run the same tests as above.
/
\bgroup
\catcode`\^^M13%
\gdef\cd@MakeShortCode[#1]#2{%
	\def\cd@TempEnv{#1}%
	\cd@BadChar{#2}{ShortCode}%
	\ifcd@BadChar%
	\else\ifcd@ShortCodeChar%
		\cd@ShortCodeError%
/

\noindent Then we check whether the environment exists,
thanks to "\"\meta{Environment}"@cd@EOL" which is defined
for \meta{Environment} when created with "\NewExample".
/
	\else%
		\expandafter\ifx\csname #1@cd@EOL\endcsname\relax%
			\cd@Error{%
				`#1' is not an example environment.\MessageBreak%
				`code' is selected instead}%
			\def\cd@TempEnv{code}%
		\fi%
/

\noindent This is the same as above: we state that a character
has been defined as a "\ShortCode".
/
		\cd@ShortCodeChartrue%
		\cd@DefErr{#2}{ShortCode}%
		\chardef\cd@ShortCodeCat=\catcode`#2%
/

\DefineMacro\cd@ShortCode
\DefineMacro\cd@ShortEnd
\DefineMacro\cd@ActivateShortCode
\noindent Then we define the character to launch the appropriate
environment, but with "\ifcd@Short§-Code" turned to true. What will
happen depends on the status of the environment. If it is the
default "code" environement, it will call "\cd@ShortCode" as
defined here, which is equivalent to "\code" itself (see below).
On the other hand, if the environment is an "example" environement,
the special example macro will be called and delimit its argument
with "\cd@ShortEnd", which is the "\ShortCode" character itself.
"\cd@ActivateShortCode" is needed to reactivate the character
in case it was one of the specials, as we did for "\ShortVerb".
/
		\bgroup%
			\lccode`\~=`#2%
			\lowercase{%
			\gdef~{\cd@ShortCodetrue\csname\cd@TempEnv\endcsname}%
			\gdef\cd@ShortEnd{~}%
			\gdef\cd@ShortCode##1^^M##2~{\cd@StartGobble##2^^?\egroup}%
			\gdef\cd@ActivateShortCode{\catcode`#2=13\relax}%
/

\DefineMacro\UndoShortCode
The rest is equivalent to "\ShortVerb" above.
/
			\gdef\UndoShortCode{%
				\ifcd@ShortCodeChar%
					\catcode`~=\cd@ShortCodeCat\relax%
					\let\cd@ActivateShortCode\relax%
					\cd@ShortCodeCharfalse%
				\else%
					\cd@UndoErr{\ShortCode}%
				\fi}}%
		\egroup%
		\catcode`#2=13 %
	\fi\fi}%
\egroup
\def\UndoShortCode{\cd@UndoErr{\ShortCode}}
/\AddBlankLine

\DefineMacro\VerbBreak
"\VerbBreak" starts as above.
/
\newif\ifcd@VerbBreak
\newtoks\cd@@Everypar

\def\VerbBreak#1{%
	\cd@BadChar{#1}{VerbBreak}%
	\ifcd@BadChar%
	\else\ifcd@VerbBreak%
		\cd@VerbBreakError%
	\else\cd@VerbBreaktrue
		\cd@DefErr{#1}{VerbBreak}%
		\bgroup%
			\lccode`\~`#1 %
			\lowercase{%
/

\DefineMacro\cd@ActivateVerbBreak
However, "\VerbBreak" characters become active
only in verbatim contexts. We create "\cd@ActivateVerbBreak"
to that end. When active the character stores the current
value of "\everypar" and then empties it (because the broken
line should start with nothing).
/
			\gdef\cd@ActivateVerbBreak{%
				\catcode`#1\active%
				\gdef~{%
					\cd@@Everypar\everypar%
					\everypar{}%
/

\noindent Then we set a scratch dimension to "\cd@FirstSpaces"
times the width of a space in the current font. "\cd@FirstSpaces"
is incremented by spaces and tabs at the beginning of each lines.
In case the current environment is numbered, we increase our
scratch dimension by the width of the box containing the number,
stored in "\"\meta{Environment}"@cd@boxwidth".
/
					\dimen0=\cd@FirstSpaces\fontdimen2\font\relax%
					\expandafter\ifx\csname\cd@ExampleName @cd@boxwidth\endcsname\relax%
					\else%
						\advance\dimen0 \csname\cd@ExampleName @cd@boxwidth\endcsname\relax%
					\fi%
/

\noindent Finally, we create a paragraph, turn to horizontal mode, restore
"\everypar" in its initial value and create a space of the desired
width, namely the same as the space at the beginning of the original broken line.
/
					\endgraf\leavevmode\everypar\cd@@Everypar\hbox to\dimen0{\hss}}}}%
		\egroup%
/

\DefineMacro\cd@IgnoreVerbBreak
The character should be ignored in "\CodeOutput", and this
is what we do here. The "\Undo..." variant simply sets these
commands to "\relax".
/
		\def\cd@IgnoreVerbBreak{\catcode`#1=9\relax}%
	\fi\fi}
\def\UndoVerbBreak{%
	\ifcd@VerbBreak%
		\let\cd@ActivateVerbBreak\relax
		\let\cd@IgnoreVerbBreak\relax
		\cd@VerbBreakfalse
	\else
		\cd@UndoErr{\VerbBreak}
	\fi}
\let\cd@ActivateVerbBreak\relax
/

\DefineMacro\VerbCommand
\DefineMacro\cd@ActivateVerbCommand
\DefineMacro\cd@IgnoreVerbCommand
\DefineMacro\UndoVerbCommand
"\VerbCommand" is similar once again. We define
"\cd@ActivateVerbCommand" to change the catcodes of the characters
to 0, 1 and 2 in verbatim contexts and "\cd@IgnoreVerbCommand"
to turn the second character into a command that gobbles 
its argument, delimited by the third character. This is
straightforward, but the first character is more complicated:
it has to gobble letters and only letters.
/
\newif\ifcd@VerbCommand

\def\VerbCommand#1#2#3{%
	\cd@BadChar{#1}{VerbCommand}%
	\cd@BadChar{#2}{VerbCommand}%
	\cd@BadChar{#3}{VerbCommand}%
	\ifcd@BadChar%
	\else\ifcd@VerbCommand%
		\cd@VerbCommandError
	\else%
		\cd@DefErr{#1, \string#2 and \string#3}{VerbCommand}
		\cd@VerbCommandtrue%
		\def\cd@ActivateVerbCommand{\catcode`#1=0 \catcode`#2=1 \catcode`#3=2\relax}%
		\def\cd@IgnoreVerbCommand{%
			\catcode`#1=13 %
			\lccode`\~=`#1 %
			\lowercase{\def~{\cd@GobbleLetters}}%
			\catcode`#2=13 %
			\lccode`\~=`#2 %
			\lowercase{\def~####1#3{}}}%
	\fi\fi}
\def\UndoVerbCommand{%
	\ifcd@VerbCommand%
		\let\cd@ActivateVerbCommand\relax%
		\let\cd@IgnoreVerbCommand\relax%
		\cd@VerbCommandfalse%
	\else%
		\cd@UndoErr{\VerbCommand}%
	\fi}%
\let\cd@IgnoreVerbCommand\relax
\let\cd@ActivateVerbCommand\relax
/

\DefineMacro\cd@GobbleLetters
Gobbling letters is not a very delicate process. We
take the next token, check whether it is of category
11, and eat it away if it is the case. That's the reason
why "\VerbCommand" is not very sound. If the next token
happens to be a macro (as might be the case since in
"\CodeOutput", since the escape character is turned back to 0),
trying to evaluate its catcode is not a good idea.
/
\def\cd@GobbleLetters#1{\ifnum\catcode`#1=11 \expandafter\cd@GobbleLetters\else\expandafter#1\fi}
/

\DefineMacro\CodeEscape
\DefineMacro\UndoCodeEscape
Finally, "\CodeEscape" doesn't do much in normal mode.
We simply check characters.
/
\newif\ifcd@CodeEscape%

\def\CodeEscape#1{%
	\cd@BadChar{#1}{CodeEscape}%
	\ifcd@BadChar%
	\else\ifcd@CodeEscape%
		\cd@CodeEscapeError%
	\else%
		\cd@CodeEscapetrue%
		\cd@DefErr{#1}{CodeEscape}%
	\fi\fi}
\def\UndoCodeEscape{%
	\ifcd@CodeEscape%
		\cd@CodeEscapefalse%
	\else%
		\cd@UndoErr{\CodeEscape}%
	\fi}%
/\AddBlankLine

\subsection{Verbatim definitions}

\DefineMacro\cd@SpaceChar
Here comes the time to do some verbatim. We start
with space. "\ifcd@Star" is the conditional switched
to true if we're in a starred verbatim environment.
We define the visible space character to be space
of category 12 in typewriter font, as usual.\cox[12pt](110,0pt,0pt,Forget me not)
/
\newif\ifcd@Star
\newif\ifcd@NewLine
\newcount\cd@FirstSpaces

\bgroup
\catcode`\ 12%
\gdef\cd@SpaceChar{\texttt{ }}%
/\AddBlankLine

\DefineMacro\cd@MakeSpace
\DefineMacro\cd@ObeySpaces
\noindent Since we want spaces at the beginning of
a line to count how many they are, so that "\VerbBreak"
can properly break the line, we don't equate the
space character with "\@xobeysp" (\LaTeX's verbatim
space) or "\cd@SpaceChar" directly; instead, "\cd@ObeySpaces"
will print the space, being called by real spaces in
"\cd@VerbTab" and "\cd@VerbSpace". ("^^I" denotes a
tab character).

/
\catcode`\^^I=13\relax%
\catcode`\ =13\relax%
\gdef\cd@MakeSpace{%
\ifcd@Star%
\let\cd@ObeySpaces\cd@SpaceChar%
\else%
\let\cd@ObeySpaces\@xobeysp%
\fi%
\catcode`\ =13\relax%
\catcode`\^^I=13\relax%
\let =\cd@VerbSpace%
\let^^I=\cd@VerbTab}%
/

\DefineMacro\cd@VerbSpace
\DefineMacro\cd@VerbTab
In verbatim contexts, a space takes the next
character as an argument; in case "\ifcd@NewLine" is true,
which it is at the beginning of every line (thanks to
an "\everypar"), it increments "\cd@FirstSpaces",
which is used by "\VerbBreak". A tab character does
the same except that the "\cd@FirstSpaces" is increased
by the value of "\TabSize" (stored in "\cd@TabSize").
In case the next character is not a space or a tab, "\ifcd@NewLine"
is set to false.

Spaces leaves a "\cd@ObeySpaces" while tabs create an
empty box of width "\TabSize" times the width of a space
in the current font.
/
\gdef\cd@VerbSpace#1{%
\cd@ObeySpaces%
\ifcd@NewLine\advance\cd@FirstSpaces1\relax\fi%
\ifx#1^^I\else\ifx#1 \else\cd@NewLinefalse\fi\fi#1}%
\gdef\cd@VerbTab#1{%
\leavevmode\hbox%
to\cd@TabSize\fontdimen2\font{\hss}%
\ifcd@NewLine\advance\cd@FirstSpaces\cd@TabSize\fi%
\ifx#1^^I\else\ifx#1 \else\cd@NewLinefalse\fi\fi#1}
\egroup
/\AddBlankLine

\DefineMacro\cd@Verbatim
Here comes the verbatimizer. First, we cancel the
parindent and sets "\hfuzz" to "\cd@Box§-Tolerance",
which stores the argument of "\BoxTolerance".
/
\def\cd@Verbatim{%
	\parindent\z@%
	\hfuzz=\cd@BoxTolerance%
/

\noindent Then, if a "\ShortVerb" was defined, we
undo it, so that it appears as any other character 
in this context. If this verbatim was called by the
"\ShortVerb" character itself, remember that it restores
itself to 13.
/
	\ifcd@ShortVerb%
		\UndoShortVerb%
	\fi%
/

\noindent If we're not in a verbatim context called
by "\ShortCode", we undo it, for the same reason.
/
	\ifcd@ShortCode%
		\else%
		\ifcd@ShortCodeChar%
			\UndoShortCode%
		\fi%
	\fi%
/

\noindent We change the usual catcodes and reactivate
the "\ShortCode" character, just in case it was changed
by "\dospecials" or "\@noligs". We activate the verb break
and the verb command, and the rest is straightforward.
/
	\let\do\@makeother\dospecials\@noligs%
	\ifcd@ShortCode%
		\cd@ActivateShortCode%
	\fi%
	\cd@ActivateVerbBreak%
	\cd@ActivateVerbCommand%
	\frenchspacing%
	\catcode`\^^M=13\relax%
	\cd@MakeSpace}%
/\AddBlankLine

\DefineMacro\BoxTolerance
\DefineMacro\TabSize
\DefineMacro\Gobble
These are pretty straigthforward too. I defined a macro instead
of a simple dimension or number, because it seems to
me that something like "\TabSize{25}" is much more 
common in the \LaTeX\ world than "\TabSize25". Besides,
a "\relax" is automatically added, which avoids errors.
/
\newdimen\cd@BoxTolerance
\def\BoxTolerance#1{\cd@BoxTolerance=#1\relax}
\def\TabSize#1{\chardef\cd@TabSize=#1\relax}
\TabSize2
\def\Gobble#1{\chardef\cd@GobbleNum=#1\relax}
\Gobble0
/\AddBlankLine

\subsection{The default \texttt{code} environment}

\DefineMacro\CodeFont
The basic "code" environment is quite simple. First,
we define "\CodeFont", which simply stores its argument
in "\cd@CodeFont", to be released later. The following
macros are explained more properly in the definition
of "\NewExample" below.
/
\def\CodeFont#1{\def\cd@CodeFont{#1}}
\CodeFont{\ttfamily}
\newcount\code@cd@LineNumber
\def\code@cd@boxwidth{0pt}
\def\code@cd@BoxStyle{\rmfamily\footnotesize}
\gdef\code@cd@LineNumberBox{%
	\global\advance\code@cd@LineNumber1\relax%
	\def\@currentlabel{\the\code@cd@LineNumber}%
	\hbox to\code@cd@boxwidth{%
	\hss%
	\code@cd@BoxStyle\relax%
	\the\code@cd@LineNumber\enspace}}%
\let\code@cd@EOL\iffalse%
/

\DefineMacro\code
We create a paragraph and stores the name of the environment
(used in "\VerbBreak" to check the width of the line number
box).
/
\def\code{%
	\endgraf%
  \bgroup%
  	\def\cd@ExampleName{code}%
/

\noindent We launch the verbatim definitions and the complicated
"\cd@ObeyLines" (see below) that makes ends of lines work properly
(gobbling characters if needed).
/
    \cd@Verbatim%
    \cd@ObeyLines%
/

\noindent Every new paragraph, i.e. every line in that
context, typeset the line number and switches some values
exlplained above. We also set the font.
/
    \everypar{%
    	\code@cd@LineNumberBox
      \cd@NewLinetrue%
      \cd@FirstSpaces0\relax}%
    \cd@CodeFont%
/

\noindent Finally, we call the proper macro, depending
on whether "\code" was called by "\begin{code}", "\begin{code*}"
or the "\ShortCode" character.
/
    \ifcd@ShortCode%
    	\global\cd@ShortCodefalse%
    	\let\cd@next\cd@ShortCode%
    \else\ifcd@Star%
    	\global\cd@Starfalse%
    	\let\cd@next\cd@StarCode%
    \else%
    	\let\cd@next\cd@Code%
    \fi\fi\cd@next}
/

\DefineMacro\invisible
\noindent The starred variant of "\code" switches to true
the conditional used just above. Let's also define the
"invisible" environment, which takes an argument delimited
by "\end{invisible}" and thus needs to turn some catcodes.
/
\expandafter\def\csname code*\endcsname{\cd@Startrue\code}
\def\invisible{%
	\bgroup%
	\catcode`\\=12 \catcode`\{=12 \catcode`\}=12 \catcode`\^^M=13 %
	\cd@Invisible}
/

The "^^?" character is used to delimit the end of the verbatim
material (this is important because all ends of line scan ahead,
see below). Since it is compared in an "\ifx" conditional, I
define it to do nothing but with a distinct definition.
/
\gdef^^?{\cd@UnlikelyCommand}
\gdef\cd@UnlikelyCommand{}
/\AddBlankLine

\DefineMacro\cd@Code
\DefineMacro\cd@StarCode
\DefineMacro\cd@Invisible
"\begin{code}" expects "\end{code}" while "\begin{code*}"
expects "\end{code*}". That's the reason why we distinguish
"\cd@Code" and "\cd@StarCode". Apart from that, they do the
same: they typeset their argument (the first one is the end
of the line) and close the environment. "\cd@StartGobble" is,
obviously, the character gobbler for the first line.
"\cd@Invisible" also matches its end but prints nothing. 
/
\begingroup
\catcode`|=0
\catcode`<=1
\catcode`>=2
\catcode`{=12
\catcode`}=12
\catcode`\^^M=13 %
\catcode`\\=12 %
|gdef|cd@Code#1^^M#2\end{code}<|cd@StartGobble#2^^?|egroup|end<code>>%
|gdef|cd@StarCode#1^^M#2\end{code*}<|cd@StartGobble#2^^?|egroup|end<code*>>%
|gdef|cd@Invisible#1^^M#2\end{invisible}<|egroup|end<invisible>|ignorespaces>%
|endgroup
/

Here comes a fastidious part. Because we want to gobble
characters at the beginning of each line (according to
"\Gobble"), ends of lines do not simply create a new
paragraph, they also give a look at the next line and
gobble the adequate number of characters. Unfortunately,
their definition changes slightly according to the
context (default "code" and examples with or without
\eTeX). Let's set the stage.
/
\newcount\cd@GobbleCount%
\begingroup
\catcode`\^^M13\relax%
/

\DefineMacro\cd@StartGobble
This is the gobbler called at the beginning of the
material enclosed in a default "code" environment.
If we meet "^^?", i.e. if the environment is empty,
we do nothing.
/
\gdef\cd@StartGobble#1{%
	\ifx#1^^?%
		\cd@GobbleCount=0 %
		\let\cd@next\relax%
/

\noindent Else, if we have reached the
value set by "\Gobble" (stored in "\cd@GobbleNum"),
we replace the token we were considering in the stream.
/
	\else\ifnum\cd@GobbleCount=\cd@GobbleNum%
		\cd@GobbleCount=0 %
		\def\cd@next{#1}%
/

\noindent If we meet an end of line character, that is, 
if the environment begins with a blank line,
we put it back too (it will create a paragraph,
among other things).
/
	\else\ifx#1^^M%
		\cd@GobbleCount=0 %
		\def\cd@next{^^M}%
/

Finally, if none of the above apply, we keep
gobbling.
/
	\else%
		\advance\cd@GobbleCount1 %
		\let\cd@next\cd@StartGobble%
	\fi\fi\fi\cd@next}%
/

\DefineMacro\cd@ObeyLines
In the "code" environment, ends of lines
act exactly like "\cd@StartGobble" except
that they create a paragraph in the first
three cases.
/
\gdef\cd@ObeyLines{%
	\def^^M##1{%
		\ifx##1^^?%
		\cd@GobbleCount=0 %
		\def\cd@next{\leavevmode\endgraf}%
	\else\ifnum\cd@GobbleCount=\cd@GobbleNum%
		\cd@GobbleCount=0 %
		\def\cd@next{\leavevmode\endgraf##1}%
	\else\ifx##1^^M%
		\cd@GobbleCount=0 %
		\def\cd@next{\leavevmode\endgraf^^M}%
	\else%
		\advance\cd@GobbleCount1 %
		\let\cd@next^^M%
	\fi\fi\fi\cd@next}}%
\endgroup
/\AddBlankLine


\subsection{Example environments}
Examples are quite different from the default "code"
environment, since they provide both the input and
the output of a code. Besides, if available, they
make use of \eTeX.

\DefineMacro\eTeXOn
\DefineMacro\eTeXOff
Here's the command to switch from \eTeX\ to external file.

/
\def\eTeXOn{%
	\@ifundefined{eTeXversion}%
		{\cd@Error{%
		You're not running on eTeX.\MessageBreak%
		Command \string\eTeXOn\space ignored}}%
		{\cd@eTeXtrue}}
\def\eTeXOff{\cd@eTeXfalse}
/

\DefineMacro\NewExample
\DefineMacro\cd@NewExample
\DefineMacro\RenewExample
\DefineMacro\cd@RenewExample
\DefineMacro\cd@GobbleThree
"\NewExample" and "\RenewExample" work similarly
but in an inverted way. Both test for options and launch
"\cd@@NewExample" on the options and example name if nothing
is wrong. Beforehand, they turn "#" into an active character,
which will be "\let" later to the code material with additional
macros.
/
\def\NewExample{%
	\@ifnextchar[%
		{\cd@NewExample}%
		{\cd@NewExample[]}}
\def\cd@NewExample[#1]#2{%
	\expandafter\ifx\csname #2\endcsname\relax
		\def\cd@next{\catcode`\#=13 \cd@@NewExample{#1}{#2}}%
	\else%
		\let\cd@next\relax%
		\cd@Error{%
		Style `#2' already defined or the name\MessageBreak%
		is already in use.\MessageBreak%
		Use \protect\RenewExample\space if you want to redefine it}%
		\let\cd@next\cd@GobbleThree%
	\fi\cd@next}

\def\RenewExample{%
	\@ifnextchar[%
		{\cd@RenewExample}%
		{\cd@RenewExample[]}}
\def\cd@RenewExample[#1]#2{%
	\expandafter\ifx\csname #2\endcsname\relax
		\let\cd@next\relax%
		\cd@Error{%
		Style `#2' is undefined.\MessageBreak%
		Use \protect\NewExample\space to redefine it}%
		\let\cd@next\cd@GobbleThree%
	\else\expandafter\ifx\csname #2\endcsname\code%
		\def\CodeFont{%
			\cd@Error{%
			You have redefined the `code' environment.\MessageBreak%
			\string\CodeFont\space is no longer operative}}
	\fi%
		\def\cd@next{\catcode`\#=13 \cd@@NewExample{#1}{#2}}%
	\fi\cd@next}

\def\cd@GobbleThree#1#2#3{}
/\AddBlankLine

\IgnorePrefix{cd@@}\DefineMacro\cd@@NewExample\IgnorePrefix{cd@}
Here is the working mechanism behind both "\NewExample" and "\RenewExample".
Since "#" will have a special function, we do some catcode changing.
The definition is "\long", of course.
/
\begingroup
\catcode`\"=6 %
\catcode`\#=13 %
\long\gdef\cd@@NewExample"1"2"3"4"5{%
/

\noindent We define some default values: "\"\meta{Example}"@cd@EOL"
is a switch used when the example is processed with \eTeX, indicating
whether ends of lines are visible or not. By default, they aren't, but
options may change it. "\"\meta{Example}"@cd@LineNumberBox" is the
command used in examples to typeset the line number. By default, it
is set to "\relax" because examples have no line number.

\DefineMacro\cd@ExampleName
We store the name of the example to be retrieved when the
environment is processed, but actually it is stored here for
the options. Finally, we analyze options with a terminator.
/
	\expandafter\gdef\csname"2@cd@EOL\endcsname{\iffalse}%
	\expandafter\let\csname"2@cd@LineNumberBox\endcsname\relax%
	\def\cd@ExampleName{"2}%
	\cd@ExampleOptions"1,cd@end,%
/

\DefineMacro\CodeInput
\DefineMacro\CodeOutput
\DefineMacro\cd@MakeExample
Now we define "\"\meta{Example}, which will be called
by "\begin"\marg{Example}, as usual in \LaTeX. Each time, it
redefines "\CodeInput" and "\CodeOutput". Both store the name
of the example, "\let" "#" to "\cd@Input" and "\cd@Output" respectively,
whose definitions depends on the way the example is processed
(\eTeX\ or not), and finally execute the definition given
by the user. "\cd@MakeExample" simply executes the last
argument; it will be called at the end of the environment. Note
the extra pairs of braces in all cases.
/
	\expandafter\def\csname"2\endcsname{%
		\gdef\CodeInput{{%
			\def\cd@ExampleName{"2}%
			\let#\cd@Input%
			"3}}%
		\gdef\CodeOutput{%
			\def\cd@ExampleName{"2}%
			\let#\cd@Output{"4}}%
		\gdef\cd@MakeExample{{"5}}%
/

\noindent Finally, we launch the example maker with the
name of the environment (to match its proper end).
/
		\cd@Example{"2}}%
/

\noindent We also define the starred version of "\"\meta{Example},
whose only difference is to switch the star conditional. Finally,
we restore the category code of "#" and close.
/
	\expandafter\def\csname"2*\endcsname{%
		\global\cd@Startrue%
		\gdef\CodeInput{{%
		\def\cd@ExampleName{"2}%
		\cd@Startrue%
		\let#\cd@Input%
		"3}}%
		\gdef\CodeOutput{%
			\def\cd@ExampleName{"2}%
			\let#\cd@Output{"4}}%
		\gdef\cd@MakeExample{{"5}}%
		\cd@Example{"2*}}%
	\catcode`\#=6\relax}%
\endgroup
/\AddBlankLine

\DefineMacro\cd@numbered
\DefineMacro\cd@continuous
\DefineMacro\cd@visibleEOL
\DefineMacro\cd@empty
Now we process options. First we define some keywords.
/
\def\cd@numbered{numbered}
\def\cd@continuous{continuous}
\def\cd@visibleEOL{visibleEOL}
\def\cd@empty{}
/

\DefineMacro\cd@ExampleOptions
This is the option processor. It is recursive and stops
when it meets the terminator. It simply stores the name
of the option and acts accordingly.
/
\def\cd@ExampleOptions#1,{%
	\def\cd@TempOption{#1}%
	\let\cd@next\cd@ExampleOptions%
	\ifx\cd@TempOption\cd@end%
		\let\cd@next\relax%
/

\noindent If the option is "numbered", we create a new
count register, set the width of the box containing the
number to 0pt by default, and define the style of this
number to be "\relax" by default too. They will be modified
by "\LineNumber".
/
	\else\ifx\cd@TempOption\cd@numbered%
		\global\expandafter\newcount\csname\cd@ExampleName @cd@LineNumber\endcsname%
		\expandafter\gdef\csname\cd@ExampleName @cd@boxwidth\endcsname{0pt}%
		\expandafter\let\csname\cd@ExampleName @cd@BoxStyle\endcsname\relax%
/

\noindent We then define the macro executed by the environment for
the line number; it increments the count, stores its value as the
current label for "\label" and "\ref", create a box of the 
desired width, flushes everything to the right, executes the style
and typeset the value of the counter.
/
		\expandafter\gdef\csname\cd@ExampleName @cd@LineNumberBox\endcsname{%
			\expandafter\advance\csname\cd@ExampleName @cd@LineNumber\endcsname1\relax%
			\def\@currentlabel{\expandafter\the\csname\cd@ExampleName @cd@LineNumber\endcsname}%
			\hbox to\csname\cd@ExampleName @cd@boxwidth\endcsname{%
				\hss%
				\csname\cd@ExampleName @cd@BoxStyle\endcsname\relax%
				\expandafter\the\csname\cd@ExampleName @cd@LineNumber\endcsname\enspace}}%
/

\noindent If the option is "continuous", we do the same thing,
except that the count register is created if and only if it
does not already exists (so that a modified "continuous" example
environment will continue where it stopped; the user may
use "\LineNumber" to start back from 0), and the "\advance"
of the count is "\global", so that the last value is always
retained from one environment to the other.
/
	\else\ifx\cd@TempOption\cd@continuous%
		\expandafter\ifx\csname\cd@ExampleName @cd@LineNumber\endcsname\relax%
			\global\expandafter\newcount\csname\cd@ExampleName @cd@LineNumber\endcsname%
		\fi%
		\expandafter\gdef\csname\cd@ExampleName @cd@boxwidth\endcsname{0pt}%
		\expandafter\let\csname\cd@ExampleName @cd@BoxStyle\endcsname\relax%
		\expandafter\gdef\csname\cd@ExampleName @cd@LineNumberBox\endcsname{%
			\global\expandafter\advance\csname\cd@ExampleName @cd@LineNumber\endcsname1\relax%
			\def\@currentlabel{\expandafter\the\csname\cd@ExampleName @cd@LineNumber\endcsname}%
			\hbox to\csname\cd@ExampleName @cd@boxwidth\endcsname{%
				\hss%
				\csname\cd@ExampleName @cd@BoxStyle\endcsname\relax%
				\expandafter\the\csname\cd@ExampleName @cd@LineNumber\endcsname\enspace}}%
/

\noindent The "visibleEOL" option simply sets the relevant conditional to "true".
/
	\else\ifx\cd@TempOption\cd@visibleEOL%
		\expandafter\gdef\csname\cd@ExampleName @cd@EOL\endcsname{\csname iftrue\endcsname}%
	\else\ifx\cd@TempOption\cd@empty%
	\else%
		\cd@Error{`#1' is not a valid option}%
	\fi\fi\fi\fi\fi\cd@next}%
/\AddBlankLine

\DefineMacro\LineNumber
\DefineMacro\cd@SetLineNumber
"\LineNumber" is straightforward. After some testing, it sets
the macro created above to the values specified. If a 
a square bracket follows, it executes "\cd@SetLineNumber".
/
\def\LineNumber#1#2#3{%
	\expandafter\ifx\csname#1@cd@EOL\endcsname\relax%
		\cd@Error{`#1' is not an example environment'}%
	\else\expandafter\ifx\csname #1@cd@LineNumber\endcsname\relax%
		\cd@Warning{%
			`#1' is not `numbered' nor `continuous'.\MessageBreak%
			\string\LineNumber\space on line \the\inputlineno\space is useless}{}%
	\else%
		\expandafter\gdef\csname #1@cd@BoxStyle\endcsname{#2}%
		\expandafter\gdef\csname #1@cd@boxwidth\endcsname{#3}%
	\fi\fi%
	\@ifnextchar[{\cd@SetLineNumber#1}\relax}
\def\cd@SetLineNumber#1[#2]{%
	\expandafter\ifx\csname#1@cd@LineNumber\endcsname\relax%
	\else%
		\csname#1@cd@LineNumber\endcsname=#2\relax%
		\expandafter\advance\csname#1@cd@LineNumber\endcsname\m@ne%
	\fi}
/\AddBlankLine

\DefineEnvironment{example}
The default "example" environment is thus easily created.
/
\NewExample{example}{\ttfamily#}{#}{}
/

\DefineMacro\CodeInput
\DefineMacro\CodeOutput
If no example has been created, these two macros yields
error messages.
/
\def\CodeInput{%
	\cd@Error{%
		No example environment has been created.\MessageBreak%
		\string\CodeInput\space is void}}
\def\CodeOutput{%
	\cd@Error{%
		No example environment has been created.\MessageBreak%
		\string\CodeOutput\space is void}}
/\AddBlankLine

\noindent And here comes the core example environment. First,
some catcode changing.
/
\begingroup
\catcode`|=0 %
\catcode`<=1 %
\catcode`>=2 %
\catcode`{=12 %
\catcode`}=12 %
\catcode`\\=12 %
/

\DefineMacro\cd@Example
This prepares the conditions for the processing
of the material. Let's start with the usual stuff:
/
|gdef|cd@Example#1<%
	|bgroup%
		|let|do|@makeother%
		|dospecials%
/

\noindent Now, if the environment was called by a "\ShortCode"
character, there is no environment to close ("\cd@EndEnv"
executes "\end"\marg{Environment}). We call "\cd@MakeExampleEnd",
defined below, on the character, and we reactivate this character
just in case it was one of the special.
/
		|ifcd@ShortCode%
			|global|let|cd@EndEnv|relax
			|expandafter|cd@MakeExampleEnd|expandafter<|cd@ShortEnd>%
			|global|cd@ShortCodefalse%
			|cd@ActivateShortCode%
/

\noindent If the environment was called by a regular
"\begin"\meta{Environment} statement, we define the proper
end (the argument comes from "\"\meta{Example}, see the definition
in "\cd@@NewExample" above). If there exists a "\ShortCode"
character, we undefine it.
/
		|else%
			|gdef|cd@EndEnv<|end<#1>>%
			|cd@MakeExampleEnd<\end{#1}>%
			|ifcd@ShortCodeChar%
				|UndoShortCode%
			|fi%
		|fi%
/

\noindent If there's a short verb, we turn it off,
we set tabs to 12 so they are written to the file
as any other character, we activate ends of lines
and in case \eTeX\ is to process the example, we
also activate comment characters (\eTeX's scanning
mechanism is peculiar and commented parts of the
code wouldn't be taken into account otherwise).
/
		|ifcd@ShortVerb%
			|UndoShortVerb%
		|fi%
		|catcode`|^^I=12 %
		|catcode`|^^M=13 %
		|ifcd@eTeX%
			|catcode`|%=13 %
		|fi%
		|cd@ExampleEnd>%
|endgroup
/

\DefineMacro\cd@MakeExampleEnd
\DefineMacro\cd@ExampleEnd
"\cd@MakeExampleEnd" defines "\cd@ExampleEnd" so that
the environment meets its proper end. It also launches
the real processing, depending on the use of \eTeX\ or not.

The argument has been passed in "\cd@Example" above, and
is either "\end"\marg{Environment} (with the proper catcodes)
or the "\ShortCode" character.

In case we're using \eTeX, we close some groups and environments,
empty "\everypar" and assign the input. We switch the star
conditional after that, because it is needed when the input
is assigned and "\cd@Verbatim" is called.

/
\begingroup
\catcode`\^^M=13 %
%
\gdef\cd@MakeExampleEnd#1{%
	\ifcd@eTeX%
		\gdef\cd@ExampleEnd##1^^M##2#1{%
			\egroup%
			\cd@EndEnv%
			\bgroup%
				\everypar{}%
				\cd@AssigneTeXInput{##2}%
			\global\cd@Starfalse}%
/

\noindent If we're not using \eTeX, we do some testing beforehand.
We just want to inform the user that we're opening an external file.
If it already exists, we keep silent.
/
	\else%
		\def\cd@ExampleEnd##1^^M##2#1{%
			\expandafter\ifx\csname cd@TestRead\endcsname\relax%
				\newread\cd@TestRead%
			\fi%
			\openin\cd@TestRead=\jobname.exp %
			\ifeof\cd@TestRead\relax%
				\cd@Warning{%
				You're not running on eTeX or you've said \string\eTeXOff.\MessageBreak%
				I create the file \jobname.exp to produce\MessageBreak%
				the example environment on line \the\inputlineno.\MessageBreak%
				You can delete it whenever you want, but\MessageBreak%
				keeping it prevents this message from reappearing.}%
			\fi%
			\closein\cd@TestRead %
/

\DefineMacro\cd@expFile
If it does not already exists, we create
the output stream "\cd@expFile", which opens
an external scratch file for example processing.
/
			\expandafter\ifx\csname cd@expFile\endcsname\relax%
				\newwrite\cd@expFile%
			\fi%
				\immediate\openout\cd@expFile=\jobname.exp %
/

\noindent We "\let" ends of lines to a macro
equivalent to the one described above for the default "code"
environment, except that each line is written to the
external file. We launch it on the material suffixed
with a complicated tail to match all cases. \tracingcommands2 \tracingmacros2 
/
			\let^^M\cd@noeTeXEOL%
			^^M##2^^?^^M^^?%§label¤eol£
/\tracingcommands0 \tracingmacros0

\noindent Finally, we close everything and assign input
once again.
/
			\egroup%
			\cd@EndEnv%
			\immediate\closeout\cd@expFile%
			\bgroup%
				\everypar{}%
				\cd@AssignInput%
			\egroup\global\cd@Starfalse}%
	\fi}%
\endgroup
/


\subsubsection{Examples without \eTeX}

\DefineMacro\cd@noeTeXEOL
Here's how ends of lines are processed when writing
the code material to an external file. If we find
"^^?", which marks the end of the material, we stop.
/
\begingroup
\catcode`\^^M\active%
\gdef\cd@noeTeXEOL#1{%
	\ifx#1^^?%
		\cd@GobbleCount=0 %
		\let^^M\relax%
		\let\cd@next\relax%
/

\noindent If we find an end of line, that means there's
a blank line, and we write it to the "jobname.exp".
/
	\else\ifx#1^^M%
		\cd@GobbleCount=0 %
		\def\cd@next{\immediate\write\cd@expFile{}\cd@noeTeXEOL}%
/

\noindent If we have gobbled enough characters, we
write the line to the external file. Otherwise, we repeat.
/
	\else\ifnum\cd@GobbleCount=\cd@GobbleNum%
		\cd@GobbleCount=0 %
		\def\cd@next{\cd@LineWrite#1}%
	\else%
		\advance\cd@GobbleCount1 %
		\let\cd@next\cd@noeTeXEOL%
	\fi\fi\fi\cd@next}%
/

\DefineMacro\cd@LineWrite
The line written is delimited by its end. This explains
the "^^?^^M^^?" suffix at the end of the material on line~\ref{eol}.
In case "\end"\marg{Example} occurs on its own line, we need
a terminator, hence the first "^^?". If it occurs at the end
of the last line, as in "... end of code\end{code}", we need
"^^M" so that the argument of "\cd@LineWrite" is properly
delimited. The first "^^?" is then written to the file, but it
expands to nothing. Since "\cd@LineWrite" calls "\cd@noeTeXEOL",
we need another delimitator, hence the second "^^?".
/
\gdef\cd@LineWrite#1^^M{\immediate\write\cd@expFile{#1}\cd@noeTeXEOL}%
/

\DefineMacro\cd@AssignInput
Now we define the macro that will be used in "\CodeInput" (where
"#" is "\let" to "\cd@Input") and "\CodeOutput" (where it is "\let"
to "\cd@Output").

\DefineMacro\cd@Input
The input is quite similar to the default "code" environment.
We define ends of lines as usual in verbatim contexts and we
read from the scratch file.
/
\newtoks\cd@Everypar
%
\gdef\cd@AssignInput{%
	\gdef\cd@Input{%
		\bgroup%
			\cd@Everypar\everypar%
			\everypar{%
				\leavevmode\csname\cd@ExampleName @cd@LineNumberBox\endcsname\relax%
				\cd@NewLinetrue\cd@FirstSpaces0\relax\the\cd@Everypar\relax}%
			\cd@Verbatim%
			\def^^M{\leavevmode\endgraf}%
			\input{\jobname.exp}%
		\egroup}%
/

\DefineMacro\cd@Output
The output also reads from the file and simply ignores
verb breaks and commands.
/
	\gdef\cd@Output{%
		\bgroup%
			\cd@IgnoreVerbBreak%
			\cd@IgnoreVerbCommand%
			\input{\jobname.exp}%
		\egroup}%
/

\noindent Finally, we execute the last argument to "\NewExample",
i.e. what was dubbed here \meta{Immediate execution}.
/
		\cd@MakeExample}%
/

\begin{invisible}
%
\end{invisible}

\subsubsection{Examples with \eTeX}
\DefineMacro\cd@AssigneTeXInput
Examples with \eTeX\ are much more complicated. We use
the "\scantokens" command, whose function is to read
its argument as if catcodes were not fixed. For instance,\\
"\def\scan#1{{\catcode`\\=12\scantokens{#1}}}"\\
"\scan\foo"\\
yields "\foo", although the backslash was an escape character
when read. The problem is that "\scantokens" interprets ends
of lines and comments characters with their current values.
Ends of lines yields a "\par" token as usual; the problem
is that this token is scanned anew, and if you have turned
the backslash to a category 12 character, it will appear as
such. Moreover, commented parts of a line are ignored. For instance,\\
"\scan{"\\
"a% mycomment"\\
""\\
"b}"\\
yields "a\par b". So "\scantokens" as it stands is not appropriate
for verbatim material.\cox(240,3pt,20pt,Progress...)

The solution is to turned ends of lines and comments to other
catcodes beforehand. Thus the previous example yields "a% mycomment^^M^^Mb^^M".
(The final end of line is added by "\scantokens".) Now we need
some hacking to produce the desired result.

\DefineMacro\cd@Input
The input begins with the usual verbatim preparation.
/
\long\gdef\cd@AssigneTeXInput#1{%
	\gdef\cd@Input{%
		\bgroup%
			\cd@Everypar\everypar%
			\everypar{%
			\leavevmode\csname\cd@ExampleName @cd@LineNumberBox\endcsname\relax%
			\cd@NewLinetrue\cd@FirstSpaces0\relax\the\cd@Everypar\relax}%
			\cd@Verbatim%
/

\noindent We define ends of lines as yet another gobbling
mechanism. We use "^^?" once again to delimit material,
and define it to make ends of lines ignored in case it
is read, so that the additional "^^M" at the end of
"\scantokens" will be ineffective.
/
			\catcode`\^^M=13 %
			\let^^M\cd@eTeXStartGobble%
			\catcode`\^^?13 %
			\def^^?{\catcode`\^^M=9\relax}%
			\scantokens{^^M#1^^?}%
		\egroup}%
/

\DefineMacro\cd@Output
Output is still worse. Even comments are active.
/
	\gdef\cd@Output{%
		\bgroup%
			\cd@IgnoreVerbBreak%
			\catcode`\^^?13 % 
			\catcode`\%=13 %
			\catcode`\^^M=13 %
/

\noindent The next step depends on the user's choice about
ends of lines. If they are visible, we process the material
as is, with special definitions of "%" and "^^M" to mimick
\TeX's normal behavior.
/
			\csname\cd@ExampleName @cd@EOL\endcsname%
				\cd@VisibleComment%
				\let^^M\cd@eTeXOutVisibleEOL%
				\def^^?{\let^^M\relax}%
				\cd@IgnoreVerbCommand%
				\scantokens{#1^^?}%
/

\noindent If ends of lines are not visible, we execute the
material beforehand with only "%", "^^M" and "^^?" effective,
to remove unwanted code. Macros are not executed because
the backslash is still of category 12. Once ends of lines
are thus processed, we scan everything anew, ignoring the
last "^^M" and "^^@", which has a special function (see below).
/
			\else%
				\cd@ActiveComment%
				\let^^M\cd@eTeXOutEOL%
				\def^^?{\catcode`\^^M9\relax}%
				\xdef\cd@exinput{#1^^?}%
				\cd@IgnoreVerbCommand%
				\catcode`\^^M=9 %
				\catcode`\^^@=9 %
				\expandafter\scantokens\expandafter{\cd@exinput}%
			\fi%
		\egroup}%
	\cd@MakeExample\egroup}%
/
\begin{invisible}
%
\end{invisible}

\DefineMacro\cd@eTeXStartGobble
\DefineMacro\cd@eTeXEOL
Once again, macros to gobble the right number of
characters at the beginning of each line. These are
for the input. It is not
possible to put "\cd@eTeXStartGobble" directly at
the beginning of "\scantokens", because the backslash
would not be understood as an escape character. Thus we
have to "\let" "^^M" to it, and once it has done its
job, make it change the meaning of "^^M" to "\cd@eTeXEOL".
(That's also the reason why we couldn't reuse the
gobble macro of the default "code" environment, although
they are quite similar.)
/
\gdef\cd@eTeXStartGobble#1{%
	\ifx#1^^?%
		\cd@GobbleCount=0 %
		\let\cd@next\relax%
	\else\ifnum\cd@GobbleCount=\cd@GobbleNum%
		\cd@GobbleCount=0 %
		\let^^M\cd@eTeXEOL%
		\def\cd@next{#1}%
	\else\ifx#1^^M%
		\cd@GobbleCount=0 %
		\let^^M\cd@eTeXEOL%
		\let\cd@next^^M%
	\else%
		\advance\cd@GobbleCount1 %
		\let\cd@next\cd@eTeXStartGobble%
	\fi\fi\fi\cd@next}%
%
\gdef\cd@eTeXEOL#1{%
	\ifx#1^^?%
		\cd@GobbleCount=0 %
		\def\cd@next{\let^^M\relax\leavevmode\endgraf}%
	\else\ifx#1^^M%
		\cd@GobbleCount=0 %
		\def\cd@next{\leavevmode\endgraf^^M}%
	\else\ifnum\cd@GobbleCount=\cd@GobbleNum%
		\cd@GobbleCount=0 %
		\def\cd@next{\leavevmode\endgraf#1}%
	\else%
		\advance\cd@GobbleCount1 %
		\let\cd@next^^M%
	\fi\fi\fi\cd@next}%
/
\begin{invisible}
%
\end{invisible}


\DefineMacro\cd@eTeXOutVisibleEOL
And now, the output. If ends of lines are visible, we set
them to create a "\par" if the next
character is another end of line (i.e. if
we find a blank line) or to put it back into
the stream otherwise, with a space before.
/
\gdef\cd@eTeXOutVisibleEOL#1{%
	\ifx#1^^?%
		\let^^M\relax%
		\let\cd@next\relax%
	\else\ifx#1^^M%
		\par%
		\let\cd@next^^M%
	\else%
		\def\cd@next{ #1}%
	\fi\fi\cd@next}%
/

\DefineMacro\cd@eTeXOutEOL
If ends of lines are not visible, i.e. if
they are processed before anything else, we do
something similar, except that we add a dummy
character, which will be ignored when the material
is scanned, but will nonetheless prevent the
formation of macro names across lines. Tail recursion
is forbidden, since this will be used in a "\edef",
so we "\expandafter" instead.
/
\catcode`\^^@=12\relax%
\gdef\cd@eTeXOutEOL#1{%
	\ifx#1^^?%
	\else\ifx#1^^M%
		\par%
		\expandafter^^M%
	\else%
	^^@ \expandafter\expandafter\expandafter#1%
	\fi\fi}%
/

\noindent Now we deal with comments. First we do
some catcode changing. (We need a comment character
since we're currently in a group where ends of lines
are active).
\begin{code}
\catcode`\/=14\relax%
\catcode`\%=13\relax/
\catcode`\ =12\relax/
\catcode`\^^I=12\relax/
\end{code}

\DefineMacro\cd@VisibleComment
\DefineMacro\cd@EatBOL
If ends of lines are visible we define comments to
eat everything until the end of the line and then
launch a macro whose sole purpose is to remove
spaces at the beginning of the next line.
\begin{code}
\gdef\cd@VisibleComment{/
\def%##1^^M{\cd@EatBOL}/
\def\cd@EatBOL##1{/
\let\cd@next\cd@EatBOL/
\ifx##1 /
\else\ifx##1^^I/
\else\ifx##1^^M/
\let\cd@next\par/
\else/
\def\cd@next{##1}/
\fi\fi\fi\cd@next}}/
\end{code}

\DefineMacro\cd@ActiveComment
\DefineMacro\cd@EatBOL
If ends of line are not visible, we do the same
in the "\expandafter" way.
\begin{code}
\gdef\cd@ActiveComment{/
\def%##1^^M{\cd@EatBOL}/
\def\cd@EatBOL##1{/
\ifx##1 /
\expandafter\cd@EatBOL/
\else\ifx##1^^I/
\expandafter\expandafter\expandafter\cd@EatBOL/
\else\ifx##1^^M/
\par/
\else/
\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter\expandafter##1/
\fi\fi\fi}}/
\endgroup
\end{code}


\subsection{File management}
Here are some simple macro for the reader's relief.

\DefineMacro\CloseFile
Closing a file in normal mode simply makes all file identification macros
unavailable.

/
\def\CloseFile#1{%
	\def\FileSource{%
		\cd@Error{%
			No file in production. \string\FileSource\space is empty}}%
	\def\FileName{%
		\cd@Error{%
			No file in production. \string\FileName\space is empty}}%
	\def\FileVersion{%
		\cd@Error{%
			No file in production. \string\FileVersion\space is empty}}%
	\def\FileDate{%
		\cd@Error{%
			No file in production. \string\FileDate\space is empty}}}
/

\DefineMacro\@cd@LineCount
That's why, in normal mode, we close a file right now. We nonetheless
create a dummy file name for the sake of "\ProduceFile" below.
/
\ifcd@produce%
	\def\FileName{}
	\def\FileVersion{}
	\def\FileDate{}
\else
	\CloseFile{}
	\def\FileSource{}
	\newcount\@cd@LineCount%
\fi
/

\DefineMacro\ProduceFile
In normal mode, the main job of "\ProduceFile" is to reset some line number
counts. In "autoclose" mode, there's only one counter, since files
are closed when a new one is opened.
/
\def\ProduceFile#1{%
	\ifcd@autoclose%
		\code@cd@LineNumber0\relax%
/

\noindent If "autoclose" is off, we allocate a count for each file,
so lines are numbered according to the file they belong to. We
store the last value for the file we're going to close (stored
in "\FileSource"), and set the line number of the code to the number
for the file we're going to (re)open. That's why we needed a dummy
"\FileSource" above, when "\ProduceFile" is executed for the first time.
/
	\else%
		\expandafter\csname\FileSource @cd@LineCount\endcsname=\code@cd@LineNumber%
		\expandafter\ifx\csname #1@cd@LineCount\endcsname\relax%
			\expandafter\newcount\csname #1@cd@LineCount\endcsname%
			\code@cd@LineNumber0\relax%
		\else%
			\expandafter\code@cd@LineNumber\csname #1@cd@LineCount\endcsname%
		\fi%
	\fi%
/

\DefineMacro\FileSource
We reset "\FileName" and others, because their definition
is optional. "\FileSource" is mandatory and is the actual
argument of "\ProduceFile". We launch the appropriate macro
if a left bracket follows.
/
	\def\FileName{%
		\cd@Error{%
			No \string\FileName\space has been given to \FileSource}}%
	\def\FileVersion{%
	\cd@Error{%
		No \string\FileVersion\space has been given to \FileSource}}%
	\def\FileDate{%
	\cd@Error{%
		No \string\FileDate\space has been given to \FileSource}}%
	\edef\FileSource{#1}%
	\@ifnextchar[%
	{\cd@GetFileName}%
	\relax}
/

\DefineMacro\cd@GetFileName
\DefineMacro\FileName
\DefineMacro\cd@GetFileVersion
\DefineMacro\FileVersion
\DefineMacro\cd@GetFileDate
\DefineMacro\FileDate
These are straightforward and don't need any comment.
\cox[6pt](30,0pt,0pt,What if \emph{I} want\\\strut\kern2pt comment?)
/
\def\cd@GetFileName[#1]{%
	\edef\FileName{#1}%
	\@ifnextchar[\cd@GetFileVersion\relax}
\def\cd@GetFileVersion[#1]{%
	\edef\FileVersion{#1}%
	\@ifnextchar[\cd@GetFileDate\relax}
\def\cd@GetFileDate[#1]{%
	\edef\FileDate{#1}}
/\AddBlankLine

\DefineMacro\Header
\DefineMacro\cd@HeaderGobble
\DefineMacro\AddBlankLine
\DefineMacro\StartIgnore
\DefineMacro\StopIgnore
\DefineMacro\DangerousEnvironment
Finally, we define those macros that have no effect
in normal mode to have, well, no effect. Since comment
signs are `other' characters in produce mode, we change
their catcode here too, so that the user may close the
argument to "\Header" after a comment sign.
/
\def\Header{\bgroup\catcode`\%=12 \cd@HeaderGobble}
\long\def\cd@HeaderGobble#1{\egroup}
\let\AddBlankLine\relax
\let\StartIgnore\relax
\let\StopIgnore\relax
\def\DangerousEnvironment#1{}
/\AddBlankLine

\begin{invisible}
%
% Definitions for the produce mode
%
\end{invisible}



\section{Produce mode}
We now turn to produce mode, where "codedoc" becomes "CodeDoc"
and strange things happen.\cox[10pt](120,0pt,20pt,\hskip-4pt Woooo, scary...)

\subsection{Messages}
\DefineMacro\cd@Tracing
\DefineMacro\cd@TChar
\DefineMacro\cd@TUChar
\DefineMacro\cd@TCode
\CD\ may be quite talkative. According to the "tracing"
option, we define some messages.
/
\ifcase\cd@tracingmode
	\def\cd@Tracing#1{}
	\def\cd@TChar#1#2{}
	\def\cd@TUChar#1{}
	\let\cd@TCode\relax
\or
	\def\cd@Tracing#1{}
	\def\cd@TChar#1#2{}
	\def\cd@TUChar#1{}
	\def\cd@TCode{\immediate\write17{%
		*** Code written from line \the\cd@ProduceLine\space to ¨\the\inputlineno\space to \cd@CurrentFile. ***}}
\or
	\def\cd@Tracing#1{\immediate\write17{On line \the\cd@ProduceLine: #1.}}
	\def\cd@TChar#1#2{
		\bgroup
			\escapechar\m@ne\cd@Tracing{`\string#1' defined as \string\\#2}
		\egroup}
	\def\cd@TUChar#1{
		\bgroup
			\escapechar\m@ne\cd@Tracing{\string\\#1 undone}
		\egroup}
	\def\cd@TCode{\immediate\write17{%
		*** Code written from line \the\cd@ProduceLine\space to ¨\the\inputlineno\space to \cd@CurrentFile. ***}}
\fi
/

\DefineMacro\cd@Error
\DefineMacro\cd@CDWarning
\DefineMacro\cd@NoFileWarning
We also define errors and warnings; there's no need to
follow \LaTeX's ordinary syntax here.
/
\def\cd@CDError#1{%
	\immediate\write17{%
		^^J! CodeDoc Error:^^J#1^^Jl.\the\cd@ProduceLine^^J }}
\def\cd@CDWarning#1{%
	\immediate\write17{%
		^^J? CodeDoc Warning: ^^J#1^^Jl.\the\cd@ProduceLine^^J }}
\def\cd@NoFileWarning{\cd@CDWarning{No file in production. This code will be lost.}}
/\AddBlankLine



\subsection{Testing strings}
In produce mode, \CD\ is a string tester; more precisely
it imitates \TeX's normal mechanism: the escape character
is turned into an active character that gathers letters
following it and executes the name they form (in a modified
fashion, however, to execute only relevant macros).

\DefineMacro\@documentclasshook
First, we redefine what happens at the end of the
class to alter the behavior of special characters.
However, we maintain comments and turn "\" into an 
active character.
/
\ifcd@produce
\def\@documentclasshook{
	\let\do\@makeother
	\dospecials
	\catcode`\^^I=12\relax
	\catcode`\%=14\relax
	\catcode`\\\active
/

\noindent By default, "\normalsize" is an error message,
so we redefine it. We start the report.
/
	\let\normalsize\relax
	\ifnum\cd@tracingmode>0 
		\immediate\write17{^^J*** CODEDOC REPORT ***^^J}
	\fi
/

\noindent We don't load any font, so there's no need
to bother with overfull boxes nor outputs. However,
by pure superstition, I prefer some care.\cox[6pt](120,0pt,0pt,\hskip-5pt Does he know\\what he's doing?)
/
	\hfuzz=100cm%
	\output={\deadcycles0\setbox0\box255}
	\everypar{}
/

\noindent Most of the following are already 0. However,
"\tracingcommands2" would explode the log file, so we
take some care once again.
/
	\tracingcommands\z@\tracingmacros\z@\tracingoutput\z@\tracingparagraphs\z@
	\tracingpages\z@\tracinglostchars\z@\tracingrestores\z@\tracingstats\z@}
\fi
/\AddBlankLine

\DefineMacro\cd@LeftBrace
\DefineMacro\cd@RightBrace
\DefineMacro\cd@LeftBracket
\DefineMacro\cd@Space
\DefineMacro\cd@Tab
\DefineMacro\cd@EndOfLine
\DefineMacro\cd@Comment
Some characters are special, to say the least.
We need to be able to recognize them.
\begin{code}
\begingroup
\catcode`\{=12 %
\catcode`\}=12 %
\catcode`\<=1 %
\catcode`\>=2 %
\gdef\cd@LeftBrace<{>
\gdef\cd@RightBrace<}>
\gdef\cd@LeftBracket<[>
\catcode`\ =12\relax
\catcode`\^^I=12\relax
\gdef\cd@Space< >
\gdef\cd@Tab<^^I>
\catcode`\^^M=12\relax%
\gdef\cd@EndOfLine<^^M>%
\catcode`\/=14\relax/
\catcode`\%=12\relax/
\gdef\cd@Comment<%>/
\endgroup
\end{code}\AddBlankLine

\DefineMacro\cd@Escape
Here comes the definition of the escape character
as itself... The backslash can't be allowed to have
catcode 0, otherwise control sequences would form and
fire. We don't want that, obviously. On the other hand,
some control sequences should be executed, so they must
be form beforehand. Here's how "\" works. First, it
stores the current line number for messages.
/
\newcount\cd@ProduceLine

\begingroup
\catcode`|=0 %
\catcode`\\=13 %
|gdef|cd@Escape{\}%
|gdef\#1{%
	|cd@ProduceLine|inputlineno%
/

\noindent Then it turns ends of lines
and comments to other characters, because
we don't want to pass them unnoticed.
If the next character is of category code
11, we start forming a control sequence.
Otherwise, we gobble it and stop.

/
	|bgroup
		|catcode`|^^M=12 %
		|catcode`|%=12 %
		|gdef|cd@MacroName{}%
		|ifnum|catcode`#1=11 %
			|def|cd@next{|cd@Gather#1}%
		|else
			|def|cd@next{|egroup|relax}
		|fi
		|cd@next}
/

\DefineMacro\cd@Gather
\DefineMacro\cd@MacroName
\DefineMacro\cd@NextChar
Forming macro names is quite simple:
if the next character is a letter, we
add it to the temporary name. Otherwise,
we store it in "\cd@NextChar" and start
doing what \TeX\ does when it has formed
a control sequence.
/
|long|gdef|cd@Gather#1{%
	|ifnum|catcode`#1=11 %
		|xdef|cd@MacroName{|cd@MacroName#1}%
		|let|cd@next|cd@Gather%
	|else%
		|gdef|cd@NextChar{#1}%
		|let|cd@next|cd@GobbleSpace%
		|fi|cd@next}
|endgroup
/\AddBlankLine

\DefineMacro\cd@GobbleSpace
That is, we skip spaces and ends of lines,
so that the \emph{real} next character will
be put next to the formed control sequence,
in case it is an argument.

In case the next argument is none of the above,
we call "\cd@Evaluate", which will expand the
macro, on the next character.
/
\long\def\cd@GobbleSpace{%
	\let\cd@next\cd@TakeNextChar
	\ifx\cd@NextChar\cd@Space
	\else\ifx\cd@NextChar\cd@Tab
	\else\ifx\cd@NextChar\cd@EndOfLine
	\else\ifx\cd@NextChar\cd@Comment
		\let\cd@next\cd@GobbleEndOfLine
	\else
		\egroup
		\def\cd@next{\expandafter\cd@Evaluate\cd@NextChar}
	\fi\fi\fi\fi\cd@next}
/

\DefineMacro\cd@TakeNextChar
\DefineMacro\cd@GobbleEndOfLine
These do what they say.
/
\long\def\cd@TakeNextChar#1{\gdef\cd@NextChar{#1}\cd@GobbleSpace}
\begingroup
\catcode`\^^M=12%
\gdef\cd@GobbleEndOfLine#1^^M#2{%
	\gdef\cd@NextChar{#2}%
	\cd@GobbleSpace}%
\endgroup
/

\DefineMacro\cd@Evaluate
Finally, we take the name thus formed, and
execute "\"\meta{Name}"@Produce". As you might
imagine, the only macros containing the "@Produce"
suffix are defined by \CD. So, most of the time,
this execution will be no more than a "\relax".
Which is exactly what we want.

/
\def\cd@Evaluate{\csname\cd@MacroName @Produce\endcsname}
/

\codeskip=3cm
\boxskip=2cm
\subsection{Macros executed in produce mode}
To understand what follows, simply remember that
"\"\meta{Macro}"@Produce" is executed when \CD\
encounters "\"\meta{Macro}. So, for instance,
"\ShortVerb@Produce" is "\ShortVerb" in produce mode.

Macro names will become quite long, so we add some
left margin.\cox[6pt](80,0pt,0pt,You could have done\\that before...)

\DefineMacro\cd@Gobble
First, some gobbler.

/
\def\cd@Gobble#1{}
/

\DefineMacro\cd@PrepareChar
Macros like "\ShortVerb" can take four kinds of argument.
If you want "+" to be a "\ShortVerb", you can say "\ShortVerb+",
"\ShortVerb\+", "\ShortVerb{+}" and "\Short§-Verb{\+}". Since
\CD\ has already considered the next character when executing
"\ShortVerb@Produce", its catcode can't be changed, and a left
brace is of category 12 and a backslash of category 13. So we have
to gobble the next character if it is one of them.

\leavevmode"\cd@PrepareChar" takes a macro as an argument and replaces
it in the stream with the next character gobbled or not.
The backslash is turned into an escape character to handle
the "\ShortVerb{\+}" case, where the left brace is gobbled;
the backslash hasn't been read yet, so we can use it.
/
\def\cd@PrepareChar#1{%
	\catcode`\\=0 %
	\def\cd@next{\expandafter#1\cd@Gobble}
	\ifx\cd@NextChar\cd@LeftBrace%
	\else\ifx\cd@NextChar\cd@Escape%
	\else%
		\def\cd@next{#1}
	\fi\fi}%
/\AddBlankLine

\DefineMacro\ShortVerb@Produce
\DefineMacro\DefineShortVerb@Produce
\DefineMacro\cd@VerbList
Thus, "\ShortVerb@Produce" calls "\cd@PrepareChar" with
"\cd@MakeShortVerb@Produce", which will do the real job
to the character. We define \textsf{fancyvrb}'s "\DefineShortVerb"
to do the same thing. "\cd@VerbList" contains all such characters,
since "\DefineShortVerb" can define several of them. It will
be used in writing environments to neutralize them.
/
\def\ShortVerb@Produce{\cd@PrepareChar\cd@MakeShortVerb@Produce\cd@next}
\let\DefineShortVerb@Produce\ShortVerb@Produce
\def\cd@VerbList{}
/

\DefineMacro\cd@MakeShortVerb@Produce
Now we inform the user that the character was "\ShortVerb"'ed.
/
\def\cd@MakeShortVerb@Produce#1{%
	\cd@TChar{#1}{ShortVerb}
/

\noindent We add it to "\cd@VerbList".
/
	\expandafter\def\expandafter\cd@VerbList\expandafter{\cd@VerbList#1,}
/

\DefineMacro\cd@ShortVerb@Produce
\DefineMacro\UndoShortVerb@Produce
And we simply define the character to gobble everything
until its next occurrence. We also define the "\Undo..." variant.
/
	\lccode`\~=`#1 %
	\lowercase{%
		\def~{\bgroup\let\do\@makeother\dospecials\catcode`#1\active\cd@ShortVerb@Produce}%
		\def\cd@ShortVerb@Produce##1~{\egroup}}%
	\def\UndoShortVerb@Produce{\cd@TUChar{ShortVerb}\catcode`#1=12\relax}%
	\catcode`#1=13 %
	\catcode`\\=13\relax}
\let\UndoShortVerb@Produce\relax
/

\DefineMacro\UndefineShortVerb@Produce
\DefineMacro\cd@UndefineShortVerb@Produce
We define a variant for \textsf{fancyvrb}, because it
takes an argument.\vskip5pt
/
\def\UndefineShortVerb@Produce{\cd@PrepareChar\cd@UndefineShortVerb@Produce\cd@next}%
\def\cd@UndefineShortVerb@Produce#1{
	\cd@TUChar{ShortVerb (from fancyvrb)}
	\catcode`#1=12 \catcode`\\=13\relax}
/\AddBlankLine

\DefineMacro\VerbBreak@Produce
\DefineMacro\cd@MakeVerbBreak@Produce
\DefineMacro\cd@IgnoreVerbBreak
\DefineMacro\UndoVerbBreak@Produce
In produce mode, the "\VerbBreak" character is simply ignored.\vskip5pt
/
\def\VerbBreak@Produce{\cd@PrepareChar\cd@MakeVerbBreak@Produce\cd@next}
\def\cd@MakeVerbBreak@Produce#1{
	\cd@TChar{#1}{VerbBreak}
	\def\cd@IgnoreVerbBreak{\catcode`#1=9\relax}
	\def\UndoVerbBreak@Produce{\cd@TUChar{VerbBreak}\let\cd@IgnoreVerbBreak\relax}
	\catcode`\\=13\relax}
\let\cd@IgnoreVerbBreak\relax
\let\UndoVerbBreak@Produce\relax
/

\DefineMacro\cd@GobbleOptions
This is useful for "\ShortCode" and also "\NewExample"
/
\def\cd@GobbleOptions#1[#2]#3{\def\cd@NextChar{#3}\expandafter#1\cd@NextChar}
/\AddBlankLine

\DefineMacro\ShortCode@Produce
We check for options.
/
\def\ShortCode@Produce{%
	\ifx\cd@NextChar\cd@LeftBracket%
		\def\cd@next{\cd@GobbleOptions\ShortCode@Produce}%
	\else%
	\cd@PrepareChar\cd@MakeShortCode@Produce
	\fi\cd@next}
/

\DefineMacro\cd@MakeShortcode@Produce
\DefineMacro\cd@ShortWriteFile
\DefineMacro\ActivateShortCode@Produce
\DefineMacro\cd@UndoShortCode@Produce
The "\ShortCode" character in produce mode is similar
to its counterpart in normal mode, except that it
follows what "code" does in this mode. So give a
look at the definition of the code environment to
understand what is going on here.
/
\begingroup
\catcode`\^^M13%
\gdef\cd@MakeShortCode@Produce#1{%
	\cd@TChar{#1}{ShortCode}
	\lccode`\~=`#1%
	\lowercase{%
	\def~{\cd@ProduceLine\inputlineno\cd@ShortCodetrue\cd@CodeWrite}%
	\def\ActivateShortCode@Produce{\catcode`#1\active}%
	\def\cd@ShortWriteFile##1^^M##2~{%
		^^M##2^^?^^M^^?%
		\ifx\cd@NoFileWarning\relax%
			\cd@TCode%
		\else%
			\cd@NoFileWarning%
		\fi\egroup}}%
	\def\UndoShortCode@Produce{\cd@TUChar{ShortCode}\catcode`#1=12\relax}%
	\catcode`\\=13 %
	\catcode`#1=13\relax}%
\endgroup
\let\ActivateShortCode@Produce\relax
\let\UndoShortCode@Produce\relax
/\AddBlankLine

\DefineMacro\VerbCommand@Produce
\DefineMacro\cd@VerbEscape@Produce
\DefineMacro\cd@TempEsc
"\VerbCommand" characters do what they do in
"\CodeOutput" in normal mode. The escape gobble
letters and the braces gobble what they contain.

First, we store the escape character for the message.
/
\def\VerbCommand@Produce{\cd@PrepareChar\cd@VerbEscape@Produce\cd@next}
\def\cd@VerbEscape@Produce#1{
	\bgroup\escapechar\m@ne\xdef\cd@TempEsc{\string#1}\egroup
/

\DefineMacro\cd@IgnoreEscape@Produce
Then we turn it into a letter gobbler.
/
	\def\cd@IgnoreEscape@Produce{
		\catcode`#1=13 
		\lccode`\~=`#1 
		\lowercase{\def~{\cd@GobbleLetters}}}
/

\noindent This is not what you think it is.
We're not considering whether the character to come
is a left brace, but whether "\cd@NextChar", i.e. the
character following "\VerbCommand", \emph{was}
a left brace; this means that a right brace is to come,
and we want to gobble it before processing what follows.
/
		\ifx\cd@NextChar\cd@LeftBrace
			\def\cd@next{\expandafter\cd@VerbBraces@Produce\cd@Gobble}
		\else
			\let\cd@next\cd@VerbBraces@Produce
		\fi\cd@next}
/

\DefineMacro\cd@VerbBraces@Produce
\IgnorePrefix{cd@@}
\DefineMacro\cd@@VerbBraces@Produce
\IgnorePrefix{cd@}
\DefineMacro\cd@IgnoreBraces@Produce
\DefineMacro\UndoVerbCommand@Produce
The rest is pretty straightforward and similar
to what we did in normal mode.
/
\def\cd@VerbBraces@Produce{\catcode`\{=1 \catcode`\}=2 \cd@@VerbBraces@Produce}
\def\cd@@VerbBraces@Produce#1#2{%
	\expandafter\cd@TChar\expandafter{\cd@TempEsc', `\string#1' and `\string#2'}{VerbCommand}
	\def\cd@IgnoreBraces@Produce{%
		\catcode`#1=13 
		\lccode`\~=`#1 
		\lowercase{\def~####1#2{}}}
	\catcode`\\=13 \catcode`\{=12 \catcode`\}=12\relax}
\def\UndoVerbCommand@Produce{
	\cd@TUChar{VerbCommand}
	\let\cd@IgnoreEscape@Produce\relax
	\let\cd@IgnoreBraces@Produce\relax}
\let\cd@IgnoreEscape@Produce\relax
\let\cd@IgnoreBraces@Produce\relax
/\AddBlankLine

\DefineMacro\CodeEscape@Produce
\DefineMacro\cd@CodeEscape@Produce
\DefineMacro\cd@ActivateCodeEscape
\DefineMacro\UndoCodeEscape@Produce
"\CodeEscape" is easy: we simply define a macro to turn
the character into an escape in code contexts.
/
\def\CodeEscape@Produce{\cd@PrepareChar\cd@CodeEscape@Produce\cd@next}
\def\cd@CodeEscape@Produce#1{%
	\cd@TChar{#1}{CodeEscape}
	\def\cd@ActivateCodeEscape{\catcode`#1=0\relax}\catcode`\\=13\relax}
\let\cd@ActivateCodeEscape\relax
\def\UndoCodeEscape@Produce{\cd@TUChar{CodeEscape}\let\cd@ActivateCodeEscape\relax}	
/\AddBlankLine

\DefineMacro\NewExample@Produce
\DefineMacro\RenewExample@Produce
These two macros launch the option gobbler
if there are any. "\cd@DangerousExample@Produce"
is defined later because it takes its argument
between braces of category 12, like other macros.
/
\def\NewExample@Produce{%
	\ifx\cd@NextChar\cd@LeftBracket%
		\def\cd@next{\cd@GobbleOptions\NewExample@Produce}%
	\else%
		\let\cd@next\cd@DangerousExample@Produce%
	\fi\cd@next}
\let\RenewExample@Produce\NewExample@Produce
/\AddBlankLine

\IgnorePrefix{cd@@}
\DefineMacro\cd@@Evaluate
\IgnorePrefix{cd@}
\DefineMacro\StartIgnore@Produce
\DefineMacro\cd@FindIgnore
\DefineMacro\cd@StopIgnore
Ignoring the input boils down to modifying the
definition of "\cd@Evaluate" until it founds
"\StopIgnore". Meanwhile, it does nothing.
/
\let\cd@@Evaluate\cd@Evaluate
\def\StartIgnore@Produce{
	\cd@Tracing{\string\StartIgnore\space found. I will ignore everything from now on}
	\let\cd@Evaluate\cd@FindIgnore}
\def\cd@FindIgnore{
	\expandafter\ifx\csname cd@\cd@MacroName\endcsname\cd@StopIgnore
		\cd@Tracing{\string\StopIgnore\space found. I resume my normal behavior}
		\let\cd@Evaluate\cd@@Evaluate
	\fi}
\def\cd@StopIgnore{\cd@StopIgnore}
/\AddBlankLine

\DefineMacro\verb@Produce
\DefineMacro\cd@VerbEater
\IgnorePrefix{cd@@}
\DefineMacro\cd@@VerbEater
\IgnorePrefix{cd@}
The produce version of \LaTeX's "\verb"
gobbles its argument after it has checked for
a star.
/
\def\verb@Produce{\count@=0 \cd@VerbEater}
\def\cd@VerbEater#1{%
	\ifcase\count@ %
		\ifx#1*
			\count@=1 %
			\let\cd@@VerbEater\cd@VerbEater
		\else
			\def\cd@@VerbEater##1#1{}
		\fi
	\else
		\def\cd@@VerbEater##1#1{}
	\fi\cd@@VerbEater}
/\AddBlankLine

\DefineMacro\DescribeMacro@Produce
\DefineMacro\DefineMacro@Produce
\DefineMacro\DescribeEnvironment@Produce
\DefineMacro\DefineEnvironment@Produce
\DefineMacro\noexpand@Produce
\DefineMacro\string@Produce
\DefineMacro\protect@Produce
The normal counterparts of these might take dangerous
arguments, so we need to neutralize them. The first
four gobble two tokens, i.e. a left brace and"/"or
an escape character, so the following macro won't form.
The last three just gobble the escape character.
/
\def\DescribeMacro@Produce#1#2{}
\def\DefineMacro@Produce#1#2{}
\def\DescribeEnvironment@Produce#1#2{}
\def\DefineEnvironment@Produce#1#2{}
\def\noexpand@Produce#1{}
\def\string@Produce#1{}
\def\protect@Produce#1{}
/

\DefineMacro\begin@Produce
\DefineMacro\end@Produce
"\begin" and "\end" statements are executed\cox[6pt](120,0pt,22pt,Stop executing things!\\They're innocent!)
if and only if there follows a left brace. This
decreases the number of possible errors. The double-"@"
versions take their arguments in `other' braces, so they
are defined later.
/
\def\begin@Produce{
	\ifx\cd@NextChar\cd@LeftBrace
		\expandafter\begin@@Produce
	\fi}
\def\end@Produce{
	\ifx\cd@NextChar\cd@LeftBrace
		\expandafter\end@@Produce
	\fi}
/\AddBlankLine

\DefineMacro\Gobble@Produce
The produce version of "\Gobble" is similar
to the normal version, except that it take cares
of braces. "\Gobble@@Produce" is defined below.
/
\def\Gobble@Produce#1{%
	\ifx\cd@NextChar\cd@LeftBrace%
		\def\cd@next{\expandafter\Gobble@@Produce\cd@NextChar}
	\else
		\def\cd@next{\chardef\cd@GobbleNum=#1\relax}%
	\fi\cd@next}
/

\DefineMacro\Header@Produce
\DefineMacro\cd@HeaderEOL
The header is an easy matter. The only thing not to
forget is to change the catcode of \bslash back to 0.
\begin{code}
\newif\ifcd@HeaderFirstLine
\begingroup
\catcode`\^^M=13 %
\catcode`\/=14 %
\catcode`\%=12 /
\gdef\Header@Produce{/
	\bgroup/
	\catcode`\^^M=13 /
	\catcode`\%=12 /
	\catcode`\\=0 /
	\Header@@Produce}/
\gdef\cd@HeaderEOL{\def^^M{^^J% }}
\endgroup
\end{code}\AddBlankLine

\DefineMacro\cd@DocumentString
\DefineMacro\cd@CodeString
\DefineMacro\cd@StarCodeString
\DefineMacro\cd@InvisibleString
\DefineMacro\cd@StoredEnvironments
We'll need these presently.
/
\def\cd@DocumentString{document}
\def\cd@CodeString{code}
\def\cd@StarCodeString{code*}
\def\cd@InvisibleString{invisible}
\def\cd@StoredEnvironments{example,verbatim,Verbatim,BVerbatim,¨LVerbatim,SaveVerbatim,VerbatimOut,Example,CenterExample,¨SideBySideExample,PCenterExample,PSideBySideExample,}
/\AddBlankLine

Here comes the macros that take their arguments
bewteen braces of category 12. The "\if..." will be needed
in "\input@Produce".
/
\newif\ifcd@everyeof
\cd@everyeoftrue

\begingroup
\catcode`\{=12 %
\catcode`\}=12 %
\catcode`\<=1 %
\catcode`\>=2 %
/

\DefineMacro\Header@@Produce
This defines "\cd@Header", which is executed in
"\ProduceFile", to write the text input by the user
to the newly opened file. The group we close was
opened in "\Header@Produce".
/
\long\gdef\Header@@Produce{#1}<
	\gdef\cd@Header<\bgroup\cd@HeaderEOL\cd@ProduceFile<\cd@Comment\space#1>\egroup>
	\egroup>
/\AddBlankLine

\DefineMacro\Gobble@@Produce
This is launched by "\Gobble@Produce"
/
\gdef\Gobble@@Produce{#1}<\chardef\cd@GobbleNum=#1\relax>
/\AddBlankLine

\DefineMacro\DangerousEnvironment@Produce
\DefineMacro\cd@DangerousExample@Produce
\DefineMacro\DefineVerbatimEnvironment
Here we add dangerous environments to the list above,
to be checked below. 

\noindent\indent"\cd@DangerousExample@Produce" has such a cumbersome
definition because it is meant to gobble the remaining
three arguments of "\NewExample" and "\RenewExample".
They might be separated by spaces, and since spaces
have category 12 in produce mode, they won't be
skipped and "\cd@DangerousExample@Produce" wouldn't
match its definition, as \TeX\ likes to say.
/
\gdef\DangerousEnvironment@Produce{#1}<
	\cd@Tracing<#1 added to dangerous environments>
	\xdef\cd@StoredEnvironments<\cd@StoredEnvironments#1,>>
\gdef\cd@DangerousExample@Produce{#1}#2{#3}#4{#5}#6{#7}<
	\cd@Tracing<#1 added to dangerous environments (CodeDoc examples)>
	\xdef\cd@StoredEnvironments<\cd@StoredEnvironments#1,>>
\let\DefineVerbatimEnvironment@Produce\DangerousEnvironment@Produce
/\AddBlankLine

\DefineMacro\begin@@Produce
"\begin" statements simply check their argument:
if it is "code", "code*" or "invisible", it turns
to writing mode. Otherwise, the name of the argument
is checked against the list of dangerous environments.
See below where normal braces are restored.
/
\gdef\begin@@Produce{#1}<
	\def\cd@TempArg<#1>
	\ifx\cd@TempArg\cd@CodeString
		\let\cd@next\cd@CodeWrite
	\else\ifx\cd@TempArg\cd@StarCodeString
		\cd@Startrue
		\let\cd@next\cd@CodeWrite
	\else\ifx\cd@TempArg\cd@InvisibleString
		\cd@Invisibletrue
		\let\cd@next\cd@CodeWrite
	\else
		\def\cd@next<\cd@CheckEnvironment<#1>>
	\fi\fi\fi\cd@next>
/

\DefineMacro\end@Produce
There's only one thing that can wake an "\end"
statement: "document". If it finds "\end{document}",
\CD\ stops. Otherwise, "\end" statements are ignored.
/
\gdef\end@@Produce{#1}<
	\def\cd@TempArg<#1>
	\ifx\cd@TempArg\cd@DocumentString
		\def\cd@next<\cd@Tracing<\string\end{document}>
		\ifnum\cd@tracingmode=0 %
		\else
			\immediate\write17<^^J*** END OF CODEDOC REPORT ***^^J>
		\fi\@@end>
	\else
		\let\cd@next\relax
	\fi\cd@next>
/

\DefineMacro\ProduceFile@Produce
\DefineMacro\CloseFile@Produce
We define these right now, to be used later.
/
\gdef\ProduceFile@Produce{#1}<\ProduceFile@@Produce<#1>>
\gdef\CloseFile@Produce{#1}<\CloseFile@@Produce<#1>>
/\AddBlankLine

\DefineMacro\input@Produce
\DefineMacro\cd@CurrentSource
We need a terribly boring definition of "\input"
for the default header, so that files are properly
tracked back to their source. Besides, "\input" in
\TeX's way, i.e. without braces, is not allowed anymore,
if it is to be read by \CD\ in produce mode. I feel
like removing the whole thing altogether.

Lines \ref{eof1} to \ref{eof2} were added in version 0.2.
I had overlooked the fact that if an "\input" file ended
with a control sequence, then the rather complicated mechanism
of "\cd@Gather" and its friends would run into the end of
the file and produce an error message. With good ol' \TeX, I
don't know how to overcome this; hence the warning.
With \eTeX, however, I use "\everyeof" to add a pair of
braces just for the sake of some harmless tokens.
Anyway, who's using \TeX\ anymore?
/
\newcount\cd@InputDepth
\gdef\input@Produce{#1}<
  \ifcd@everyeof§label¤eof1£
    \cd@everyeoffalse
    \ifx\everyeof\@undefined
      \cd@CDWarning<%
        You're not running on e-TeX; the \string\input\space of files might be problematic.%
        ^^JAdd `{}' at the end of \string\input\space files if you ever get a `File ended...' ¨message>
    \else
      \everyeof<{}>
    \fi
  \fi§label¤eof2£
	\cd@Tracing<\string\input\space file #1>
	\expandafter\let\csname cd@MasterSource\the\cd@InputDepth\endcsname\cd@CurrentSource
	\edef\cd@CurrentSource<#1 (\string\input\space in \cd@CurrentSource)>
	\advance\cd@InputDepth1\relax
	\@@input #1\relax
	\advance\cd@InputDepth-1\relax
	\expandafter\let\expandafter\cd@CurrentSource\csname cd@MasterSource¨\the\cd@InputDepth\endcsname>
/\AddBlankLine

\DefineMacro\cd@MakeSpecialEater
\DefineMacro\cd@SpecialEater
If we find a dangerous environment, we launch
this on its name, which eats everything until
"\end"\marg{Name}.
/
\catcode`\|=0 %
\catcode`\\=13 %
|gdef|cd@MakeSpecialEater#1<
	|long|def|cd@SpecialEater##1\end{#1}<>
	|cd@SpecialEater>
|endgroup
/\AddBlankLine

\DefineMacro\cd@CurrentSource
Back to normal braces. This is a default value needed
in "\input@Produce". The extension is just a guess, of
course.
/
\edef\cd@CurrentSource{\jobname.tex}
/\AddBlankLine

\DefineMacro\cd@CheckEnvironment
\IgnorePrefix{cd@@}
\DefineMacro\cd@@CheckEnvironment
\IgnorePrefix{cd@}
This is the checking mechanism used in "\begin"
statement to detect dangerous environments. Note
that we check all environments in their starred
version too.
/
\def\cd@CheckEnvironment#1{
	\def\cd@TempEnv{#1}
	\expandafter\cd@@CheckEnvironment\cd@StoredEnvironments cd@end,}
\def\cd@@CheckEnvironment#1,{
	\def\cd@@TempEnv{#1}
	\def\cd@@StarTempEnv{#1*}
	\ifx\cd@@TempEnv\cd@end
		\let\cd@next\relax
	\else\ifx\cd@@TempEnv\cd@TempEnv
		\def\cd@next{\cd@MakeSpecialEater{#1}}
	\else\ifx\cd@@StarTempEnv\cd@TempEnv
		\def\cd@next{\cd@MakeSpecialEater{#1*}}
	\else
		\let\cd@next\cd@@CheckEnvironment
	\fi\fi\fi
	\cd@next}
/


\subsection{Writing environments}
\CD\ looks for "code", "code*" and "invisible" environments
and process them line by line.

\DefineMacro\cd@MakeOther
First, we need a recursive catcode changer.
/
\def\cd@MakeOther#1,{%
	\def\cd@TempArg{#1}%
	\ifx\cd@TempArg\cd@end%
	\else%
		\catcode`#1=12 %
		\expandafter\cd@MakeOther%
	\fi}
/\AddBlankLine

\DefineMacro\cd@CodeWrite
This is the writing macro, called by "\begin"
when the appropriate argument is found, or
by the "\ShortCode" character. "\dospecials"
is probably useless since all specials are
already done, but at least it changes the
category of the escape and the comment.
/
\newif\ifcd@Invisible
\begingroup
\catcode`\^^M=13\relax%
\gdef\cd@CodeWrite{%
	\bgroup%
		\let\do\@makeother%
		\dospecials%
		\catcode`\^^I=12 %
/

\noindent We turn all verb characters (defined
by \textsf{fancyvrb}'s "\DefineShortVerb") into
other characters, ignore the verb break, neutralize
the short code if we're not in a short code environment
(the redefinition of "\cd@TUChar" just prevents an
unwanted message sent to the user if "tracing" is 2)
an reactivate it otherwise,
ignore "\VerbCommand" and activate "\CodeEscape".
We turn ends of lines into proper gobbler once again.
/
		\expandafter\cd@MakeOther\cd@VerbList cd@end,%
		\cd@IgnoreVerbBreak%
		\ifcd@ShortCode%
			\ActivateShortCode@Produce%
		\else%
			\let\cd@TempTUChar\cd@TUChar
			\def\cd@TUChar##1{}
			\UndoShortCode@Produce%
			\let\cd@TUChar\cd@TempTUChar
		\fi%
		\cd@IgnoreEscape@Produce%
		\cd@IgnoreBraces@Produce%
		\cd@ActivateCodeEscape%
		\catcode`\^^M=13\relax%
		\let^^M\cd@produceEOL%
/

\noindent Finally we launch the adequate macro.
They all do the same thing, but they look for
different "\end" statements.
/
		\ifcd@ShortCode%
			\global\cd@ShortCodefalse\let\cd@next\cd@ShortWriteFile%
		\else\ifcd@Star%
			\global\cd@Starfalse\let\cd@next\cd@StarWriteFile%
		\else\ifcd@Invisible%
			\global\cd@Invisiblefalse\let\cd@next\cd@InvisibleWriteFile%
		\else%
			\let\cd@next\cd@WriteFile%
		\fi\fi\fi\cd@next}%
/

\DefineMacro\cd@ProduceEOL
\DefineMacro\cd@LineWrite@Produce
This is similar to the version for examples 
without \eTeX\ in normal mode, i.e. it writes
to an external file, specified in "\cd@ProduceFile".
/
\gdef\cd@produceEOL#1{%
	\ifx#1^^?%
		\cd@GobbleCount=0 %
		\let^^M\relax%
		\let\cd@next\relax%
	\else\ifx#1^^M%
		\cd@GobbleCount=0 %
		\def\cd@next{\cd@ProduceFile{}\cd@produceEOL}%
	\else\ifnum\cd@GobbleCount=\cd@GobbleNum%
		\cd@GobbleCount=0 %
		\def\cd@next{\cd@LineWrite@Produce#1}%
	\else%
		\advance\cd@GobbleCount1 %
		\let\cd@next\cd@produceEOL%
	\fi\fi\fi\cd@next}%
\gdef\cd@LineWrite@Produce#1^^M{\cd@ProduceFile{#1}\cd@produceEOL}%
/

\DefineMacro\cd@WriteFile
\DefineMacro\cd@StarWriteFile
\DefineMacro\cd@InvisibleWriteFile
And here is the end. It is the first "^^M", "\let"
to "\cd@ProduceEOL", which launches everything.
The conditional switches between an error message
(no file in production) and a report (code written).
/
\catcode`|=0 %
\catcode`<=1 %
\catcode`>=2 %
\catcode`{=12 %
\catcode`}=12 %
\catcode`\\=12 %
|long|gdef|cd@WriteFile#1^^M#2\end{code}<%
	^^M#2^^?^^M^^?%
	|ifx|cd@NoFileWarning|relax%
		|cd@TCode%
	|else%
		|cd@NoFileWarning%
	|fi|egroup>%
|long|gdef|cd@StarWriteFile#1^^M#2\end{code*}<%
	^^M#2^^?^^M^^?%
	|ifx|cd@NoFileWarning|relax%
		|cd@TCode%
	|else%
		|cd@NoFileWarning%
	|fi|egroup>%
|long|gdef|cd@InvisibleWriteFile#1^^M#2\end{invisible}<%
	^^M#2^^?^^M^^?%
	|ifx|cd@NoFileWarning|relax%
		|cd@TCode%
	|else%
		|cd@NoFileWarning%
	|fi|egroup>%
|endgroup
/\AddBlankLine





\subsection{File management}
This the final step: handling files in produce mode.\cox[9pt](120,-6cm,30pt,This sounds strange)

\DefineMacro\cd@Closed
\DefineMacro\cd@Open
\DefineMacro\cd@Wait
First, some keywords.
/
\def\cd@Closed{closed}
\def\cd@Open{open}
\def\cd@Wait{wait}
/\AddBlankLine

\DefineMacro\cd@CurrentFile
\DefineMacro\cd@ProduceFile
\DefineMacro\AddBlankLine@Produce
Some basic definitions. "\@unused" is \LaTeX's
unattributed stream for messages. We let it write
to he log file. "\cd@ProduceFile" is the writing
macro (used in writing environments above); as long
as no file is open, it does nothing.
/
\newcount\cd@ProduceCount

\def\cd@CurrentFile{}
\chardef\@unused=17
		
\def\cd@ProduceFile#1{}
\def\AddBlankLine@Produce{\cd@ProduceFile{}}
/\AddBlankLine

\DefineMacro\ProduceFile@@Produce
This is called by "\ProduceFile", via "\ProduceFile@Produce"
above. If the file is closed ore already in production,
we signal it to the user:
/
\def\ProduceFile@@Produce#1{%
	\let\cd@next\relax
	\expandafter\ifx\csname #1@Status\endcsname\cd@Closed
		\cd@CDError{%
		File `#1' has already been closed.^^J%
		If I open it again, it will be erased.^^J%
		I can't do that. I quit. Sorry.}
		\let\cd@next\@@end
	\else\expandafter\ifx\csname #1@Status\endcsname\cd@Open
		\cd@CDWarning{%
		File `#1' is currently in production.^^J%
		Why do you try to open it again?}
/

\noindent The file is waiting if it has been opened previously
and another one has been opened too afterward, provided
"autoclose" is off. In which case, we set it to "open":
/
	\else\expandafter\ifx\csname #1@Status\endcsname\cd@Wait
		\expandafter\let\csname #1@Status\endcsname\cd@Open
/

\noindent We disable the warning about the absence of
a file in production and define "\cd@ProduceFile" to
write to this file.
/
		\let\cd@NoFileWarning\relax
		\def\cd@ProduceFile{\immediate\write\csname #1@Stream\endcsname}
/

\noindent We set the current file to "wait" and define
the one we're dealing with to be the current file.
/
		\expandafter\let\csname \cd@CurrentFile @Status\endcsname\cd@Wait
		\def\cd@CurrentFile{#1}
/

\noindent Now, if the file has never been opened, we need
an output stream. If they were all allocated, we look whether
some were made available thanks to a "\CloseFile".
/
	\else\ifnum\cd@ProduceCount>15
		\chardef\cd@ProduceStream=16
		\expandafter\cd@FindStream\cd@StreamList cd@end,
/

\noindent If no stream is found, \CD\ feels so bad that it quits.
/
		\ifnum\cd@ProduceStream=16 %
			\cd@CDError{%
			No more stream for a new file. Close one with \string\CloseFile\space^^J%
			(or use the `autoclose' option).^^J%
			This situation makes me feel bad. I quit.}
			\let\cd@next\@@end
/

\noindent Else, we're very happy, and if there is
already a file in production, we close it or let it
wait.
/
		\else
			\cd@Tracing{I will now produce file #1}
			\ifx\cd@CurrentFile\cd@empty
			\else
				\ifcd@autoclose
					\cd@Tracing{I close file \cd@CurrentFile\space (autoclose mode)}
					\expandafter\let\csname \cd@CurrentFile @Status\endcsname\cd@Closed
				\else
					\expandafter\let\csname \cd@CurrentFile @Status\endcsname\cd@Wait
				\fi
			\fi
/

\noindent Then we define our file as the current one,
let the world know that it is open, allocate the stream
to its name, open it, etc., and launch a macro to retrieve
some information if any.
/
			\def\cd@CurrentFile{#1}
			\expandafter\let\csname #1@Status\endcsname\cd@Open
			\expandafter\chardef\csname #1@Stream\endcsname\cd@ProduceStream
			\immediate\openout\cd@ProduceStream=#1 %
			\let\cd@NoFileWarning\relax
			\def\cd@ProduceFile{\immediate\write\cd@ProduceStream}
			\let\cd@next\cd@GetFile@Produce
		\fi
/

\noindent If there was an available stream in the first
place, we do exactly the same.
/
	\else\chardef\cd@ProduceStream\cd@ProduceCount
		\cd@Tracing{I will now produce file #1}
		\ifx\cd@CurrentFile\cd@empty
		\else
			\ifcd@autoclose
				\cd@Tracing{I close file \cd@CurrentFile\space (autoclose mode)}
				\expandafter\let\csname \cd@CurrentFile @Status\endcsname\cd@Closed
			\else
				\expandafter\let\csname \cd@CurrentFile @Status\endcsname\cd@Wait
			\fi
		\fi
		\def\cd@CurrentFile{#1}
		\expandafter\let\csname #1@Status\endcsname\cd@Open
		\expandafter\chardef\csname #1@Stream\endcsname\cd@ProduceStream
		\immediate\openout\cd@ProduceStream=#1 %
		\let\cd@NoFileWarning\relax
		\def\cd@ProduceFile{\immediate\write\cd@ProduceStream}
		\ifcd@autoclose
		\else
			\advance\cd@ProduceCount\@ne
		\fi
		\let\cd@next\cd@GetFile@Produce
	\fi\fi\fi\fi\cd@next}
/\AddBlankLine

\DefineMacro\cd@GetFile@Produce
\DefineMacro\cd@GetFileName@Produce
\DefineMacro\cd@GetFileVersion@Produce
\DefineMacro\cd@GetFileDate@Produce
This is designed to retrieve optional information
following "\ProduceFile". We undo the "\ShortVerb"
and "\ShortCode" because they might appear there.
(My "\ShortCode" is a slash, which is used in date too.)
We also set the backslash as an escape character,
because control sequences might appear here.

In all cases, if nothing follows, and if the "noheader"
option is off, we write the header to the file.
/
\def\cd@GetFile@Produce{
	\bgroup
		\UndoShortCode@Produce
		\UndoShortVerb@Produce
		\gdef\FileName{}
		\gdef\FileVersion{}
		\gdef\FileDate{}
		\@ifnextchar[
			{\catcode`\\\z@ \cd@GetFileName@Produce}
			{\ifcd@noheader\else\cd@Header\fi\egroup}}
\def\cd@GetFileName@Produce[#1]{
	\xdef\FileName{#1}
	\catcode`\\\active
	\@ifnextchar[
		{\catcode`\\\z@ \cd@GetFileVersion@Produce}
		{\ifcd@noheader\else\cd@Header\fi\egroup}}
\def\cd@GetFileVersion@Produce[#1]{%
	\xdef\FileVersion{#1}
	\catcode`\\\active
	\@ifnextchar[
		{\catcode`\\\z@ \cd@GetFileDate@Produce}
		{\ifcd@noheader\else\cd@Header\fi\egroup}}
\def\cd@GetFileDate@Produce[#1]{%
	\xdef\FileDate{#1}
	\ifcd@noheader\else\cd@Header\fi\egroup}
/\AddBlankLine

\DefineMacro\CloseFile@@Produce
Closing a file is a lot of uninteresting testing...
/
\def\CloseFile@@Produce#1{
	\ifcd@autoclose
		\expandafter\ifx\csname #1@Status\endcsname\relax
			\cd@CDWarning{%
				You haven't opened `#1'. Closing it does nothing.^^J%
				Besides, you're in autoclose mode. \string\CloseFile\space is redundant.}
		\else\expandafter\ifx\csname #1@Status\endcsname\cd@Closed
			\cd@CDWarning{%
				`#1' was already closed. Closing it again does nothing.^^J%
				Besides, you're in autoclose mode. \string\CloseFile\space is redundant.}
		\else
			\cd@CDWarning{%
				You're in autoclose mode.	\string\CloseFile\space is redundant.}
		\fi\fi%
	\else
		\expandafter\ifx\csname #1@Status\endcsname\relax
			\cd@CDWarning{%
				You haven't opened `#1'. Closing it does nothing.}
		\else\expandafter\ifx\csname #1@Status\endcsname\cd@Closed
			\cd@CDWarning{%
				`#1' was already closed. Closing it again does nothing.}
/

\noindent If everything is okay, beside closing
the file, we also define the no-file warning and neutralize
the writing macro. We also add the stream allocated
to that file to "\cd@StreamList", so that it may be retrieved
if all other streams are unavailable.
/
		\else
			\cd@Tracing{I close file #1}
			\expandafter\let\csname #1@Status\endcsname\cd@Closed
			\def\cd@TempFile{#1}
			\ifx\cd@TempFile\cd@CurrentFile
				\def\cd@NoFileWarning{\cd@CDWarning{No file in production. ¨This code will be lost.}}
				\def\cd@ProduceFile##1{}%
			\fi
			\edef\cd@StreamList{%
				\cd@StreamList\expandafter\the\csname #1@Stream\endcsname,}
	\fi\fi\fi}
/\AddBlankLine

\DefineMacro\cd@StreamList
\DefineMacro\cd@BuildList
The last thing to do is to build that list of streams
made available by the closing of a file.
/
\def\cd@StreamList{}
\def\cd@BuildList#1cd@end,{\def\cd@StreamList{#1}}
/

\DefineMacro\cd@FindStream
When we look for a stream, we simply check
the content of "\cd@BuildList", and if we find
the terminator, this means that no stream has been
made available. Otherwise, we define "\cd@ProduceStream",
which will be allocated to the file we're trying to open,
as the first stream we find in the list, and we rebuild
the latter with the remaining numbers.
/
\newif\ifcd@stream
\def\cd@FindStream#1,{%
	\def\cd@TempArg{#1}
	\ifx\cd@TempArg\cd@end
		\cd@streamfalse
		\let\cd@@next\relax
	\else
		\cd@streamtrue
		\chardef\cd@ProduceStream=#1 %
		\let\cd@@next\cd@BuildList
	\fi\cd@@next}
/\AddBlankLine

\DefineMacro\cd@Header
Finally, here's the default header.
/
\catcode`\%=12\relax
\edef\cd@Header{
\noexpand\cd@ProduceFile{% This is \noexpand\FileName, produced by the CodeDoc class
^^J% with the `produce' option on.
^^J%
^^J% To create the documentation, compile \cd@CurrentSource
^^J% without the `produce' option.
^^J%
^^J% SOURCE: \noexpand\cd@CurrentSource
^^J% DATE: \noexpand\FileDate
^^J% VERSION: \noexpand\FileVersion
}}
\catcode`\%=14\relax
/\AddBlankLine

\noindent ... and we say goodbye. The end.\cox[6pt](0,-8pt,10pt,\hskip4pt See you!)
/
\makeatother
/

\def\section*#1{\part{#1}
\itshape
This index was generated by the \emph{\texttt{\bslash DescribeMacro}}-like
commands. It only reports where macros are described (page numbers in
normal font) and defined (page numbers in italics).
In the current version, \CD\ does not index macros when used in the code.

Entries are sorted ignoring the \emph{\texttt{cd@}} and \emph{\texttt{cd@@}} prefixes.\vskip1em}
\let\partname\relax
\let\thepart\relax
\catcode`\Z=0 
\leftskip0pt
\printindex
\catcode`\Z=11 

\end{document}