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%
% \iffalse   /!\  this file contains non-ascii --  encoding is utf-8 /!\
%
%    xargs package by Manuel P\'egouri\'e-Gonnard <mpg@elzevir.fr>
%    -------------------------------------------------------------
%
% This work may be distributed and/or modified under the conditions of
% the LaTeX Project Public License, either version 1.3c of this license
% or (at your option) any later version.  The latest version of this
% license is in:
%
%   http://www.latex-project.org/lppl.txt
%
% and version 1.3c or later is part of all distributions of LaTeX
% version 2006/05/20 or later.
%
% This work has the LPPL maintenance status `maintained'.
%
% The current maintainer of this work is Manuel P\'egouri\'e-Gonnard.
%
% This work consists of the file xargs.dtx and the derived files
% xargs.sty, xargs.pdf and xargs-fr.pdf.
%
%
%<*gobble>
\ProvidesFile{xargs.dtx}
%</gobble>
%<package>\NeedsTeXFormat{LaTeX2e}
%<package>\ProvidesPackage{xargs}
%<*package>
% \fi
% \ProvidesFile{xargs.dtx}
  [2008/03/08 1.09 \space extended macro definitions \space (mpg)]
% \iffalse
%</package>
% \fi
% \CheckSum{786}
% \CharacterTable
%  {Upper-case    \A\B\C\D\E\F\G\H\I\J\K\L\M\N\O\P\Q\R\S\T\U\V\W\X\Y\Z
%   Lower-case    \a\b\c\d\e\f\g\h\i\j\k\l\m\n\o\p\q\r\s\t\u\v\w\x\y\z
%   Digits        \0\1\2\3\4\5\6\7\8\9
%   Exclamation   \!     Double quote  \"     Hash (number) \#
%   Dollar        \$     Percent       \%     Ampersand     \&
%   Acute accent  \'     Left paren    \(     Right paren   \)
%   Asterisk      \*     Plus          \+     Comma         \,
%   Minus         \-     Point         \.     Solidus       \/
%   Colon         \:     Semicolon     \;     Less than     \<
%   Equals        \=     Greater than  \>     Question mark \?
%   Commercial at \@     Left bracket  \[     Backslash     \\
%   Right bracket \]     Circumflex    \^     Underscore    \_
%   Grave accent  \`     Left brace    \{     Vertical bar  \|
%   Right brace   \}     Tilde         \~}
% \iffalse
%<*gobble>
\begingroup
%</gobble>
%<*batchfile>
\input docstrip
\keepsilent
\preamble

xargs package by Manuel P\string\'egouri\string\'e-Gonnard %
<mpg@elzevir.fr>
This is a generated file. See xargs.dtx for license information.

\endpreamble
\askforoverwritefalse
%\generate{\file{xargs.ins}{\from{xargs.dtx}{batchfile}}}
%\generate{\file{xargs.drv}{\from{xargs.dtx}{driver}}}
\generate{\file{xargs.sty}{\from{xargs.dtx}{package}}}
\generate{\file{xargs-fr.drv}{\from{xargs.dtx}{pilote}}}
%</batchfile>
%<*gobble>
\endgroup
%</gobble>
%<*driver|pilote>
\documentclass[oneside, a4paper]{ltxdoc}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}
\usepackage{lmodern}
\usepackage{fixltx2e, mparhack}
\usepackage[babel=true, expansion=false]{microtype}
\usepackage{xargs}
\expandafter\newif\csname iffrenchdoc\endcsname % cachez ce if que je ne...
%<pilote>\frenchdoctrue
%</driver|pilote>
%<*gobble>
\iffrenchdoc
%</gobble>
%<*pilote>
\usepackage[lmargin=4.5cm, rmargin=3cm]{geometry}
\OnlyDescription
\usepackage[english, frenchb]{babel}
\FrenchFootnotes
\newcommand*\eng[1]{\emph{\foreignlanguage{english}{#1}}}
\usepackage[bookmarks=false, colorlinks=true,
  linkcolor=black, urlcolor=black]{hyperref}
%</pilote>
%<*gobble>
\else
%</gobble>
%<*driver>
\AlsoImplementation
\usepackage[english]{babel}
\usepackage[bookmarks=true, colorlinks=true,
  linkcolor=black, urlcolor=black]{hyperref}
\usepackage[nohints, undotted, english]{minitoc}
%</driver>
%<*gobble>
\fi
%</gobble>
%<*driver|pilote>
\newcommand\pf{\textsf}
\settowidth\MacroIndent{\rmfamily\scriptsize 000\ }
\setlength\MacroTopsep{0pt}
\begin{document}
  \DocInput{xargs.dtx}
\end{document}
%</driver|pilote>
%<*package>
% \fi
%
% \GetFileInfo{xargs.dtx}
%
% \title{\iffrenchdoc L'extension \pf{xargs}\else The \pf{xargs} package\fi}
% \author{Manuel Pégourié-Gonnard\\ 
%   \href{mailto:mpg@elzevir.fr}{mpg@elzevir.fr}}
% \date{\fileversion\ (\filedate)}
%
% \maketitle
% \iffrenchdoc\else 
%   \dosecttoc
%   \mtcsetrules{*}{off}
%   {\setcounter{tocdepth}{1}\tableofcontents}
%   {\setcounter{tocdepth}{2}\faketableofcontents}
% \fi
%
%         \section{Introduction}
%
% \iffrenchdoc
%
% \LaTeXe{} permet de définir facilement des commandes ayant un argument
% optionel. Cependant, il y a deux restrictions : il peut y avoir au plus un
% argument optionel, et ce doit être le premier. L'extension \pf{xargs}
% fournit des versions étendues de \cs{newcommand} et de ses analogues
% standard, qui ne présentent pas ces restrictions.
%
% Vous connaissez peut-être des astuces pour définir des commandes avec
% plusieurs arguments optionels, ou avec l'argument optionel en dernier. Mais
% utiliser ces astuces vous force à résoudre certains problèmes (ordre
% d'utilisation des arguments, gestions des espaces) qui peuvent s'avérer
% délicats. C'est n'est de toute façon pas le genre de choses auxquelles vous
% devriez avoir à réfléchir quand vous rédigez un document.
%
% L'extension \pf{xargs} vous fournit donc un moyen pratique et (je l'espère)
% robuste de définir de telles commandes, avec une syntaxe intuitive de la
% forme \meta{clé}=\meta{valeur}.
%
% \else
%
% Defining commands with an optional argument is easy in \LaTeXe{}. There is,
% however, two limitations: there can be at most one optional argument and it
% must be the first one. The \pf{xargs} package provide extended variants of
% \cs{newcommand} \& friends, for which these limitations no longer hold.
%
% You may know some tricks in order to define commands with many optional
% arguments, or with last argument optional, etc. Theses tricks are subject to
% a few problems (using arguments in arbitrary order can be difficult,
% sometimes space is gobbled where it should not), which can be difficult to
% solve.  Anyway, you don't want to worry about such tricky things while
% writing a document.
%
% The \pf{xargs} package provides you with an easy and (hopefully) robust way
% to define such commands, using a nice \meta{key}=\meta{value} syntax.
%
% \fi
%
%         \section{Usage}
%
% \iffrenchdoc
%
% L'extension \pf{xargs} fournit des analogues de toutes les macros de
% \LaTeXe{} relatives à la définition de macros. Les macros de \pf{xargs} ont
% le même nom que leur analogue standard, mais avec un |x| supplémentaire à la 
% fin : par exemple, \cs{newcommandx}, \cs{renewcommandx} ou encore
% \cs{newenvironmentx}.  Elles ont par ailleurs toutes la même syntaxe. Je ne
% présenterai donc que \cs{newcommandx}.
%
% Commençons par un exemple. Après la définition
% \begin{center}
% |\newcommandx*\vect[3][1=1, 3=n]{(#2_{#1},\ldots,#2_{#3})}|
% \end{center}
% \newcommandx*\vect[3][1=1, 3=n]{(#2_{#1},\ldots,#2_{#3})}%
% vous pouvez utiliser la macro \cs{vect} d'une des façons suivantes :
% \begin{center}
% \begin{tabular}{ll}
% |$\vect{x}$| & $\vect{x}$ \\
% |$\vect[0]{y}$| & $\vect[0]{y}$ \\
% |$\vect{z}[m]$| & $\vect{z}[m]$ \\
% |$\vect[0]{t}[m]$| & $\vect[0]{t}[m]$ \\
% \end{tabular}
% \end{center}
%
% Vous avez sans doute compris qu'il s'agit d'une macro prenant trois
% arguments au total, mais dont le premier et le troisième argument sont
% optionnels. Ils ont chacun une valeur par défaut (respectivement |1| et |n|
% ici). Vous pouvez également remarquer que la syntaxe de \cs{newcomandx} est
% très proche de celle de \cs{newcommand}, la seule différence étant qu'au
% lieu d'indiquer la valeur par défaut de l'unique argument optionel, vous
% indiquez ici le numéro de chaque argument à rendre optionel, suivi de sa
% valeur par défaut.
%
% Détaillons maintenant la syntaxe de \cs{newcommandx}, qui, répétons-le, est
% aussi la syntaxe de toutes les autres commandes de l'extension \pf{xargs}.
% (Pendant qu'on est dans les détails, voici la liste complète de ces
% commandes : \cs{newcommandx} et \cs{renewcommandx} pour les macros simples,
% \cs{providecommandx} pour s'assurer qu'une macro existe,
% \cs{DeclareRobustCommandx} pour (re)définir une macro robuste,
% \cs{CheckCommandx} pour vérifier le sens d'une macro, \cs{newenvironmentx}
% et \cs{renewenvironmentx} pour les environnements.)
%
% \begin{center}
% \cs{newcommandx} \meta{|*|} \marg{commande} \oarg{nombre} \oarg{liste}
% \marg{définition}
% \end{center}
%
% Rappellons brièvement tout ce qui est commun avec la syntaxe usuelle, à
% savoir tout sauf \meta{liste}. Si une |*| est présente, elle signifie que la
% macro crée est \emph{courte} au sens de \TeX{}, c'est-à-dire que ses
% arguments ne peuvent pas contenir de saut de paragraphe (\cs{par} ou ligne
% vide). La \meta{commande} est n'importe quelle séquence de contrôle, que
% vous pouvez ou non entourer d'accolades suivant vos goûts. Le \meta{nombre}
% définit le nombre total d'argument de la \meta{commande}, c'est un entier
% compris entre $0$ et $9$. La \meta{définition} est un texte équilibré en
% accolades, et où chaque caractère |#| est suivi soit d'un chiffre
% représentant un des arguments, soit d'un autre caractère |#|. Les arguments
% entre crochets sont optionnels.
%
% La partie intéressante maintenant. La \meta{liste} est une\ldots{} liste (!)
% d'éléments de la forme \meta{chiffre}=\meta{valeur}, séparés par des
% virgules.  Le \meta{chiffre} doit être un entier compris entre $1$ et le
% nombre d'arguments, donné par \meta{nombre}. La \meta{valeur} est n'importe
% quelle texte équilibré en accolades. Il peut être vide si vous le souhaitez
% : le signe égal qui le précède est alors optionel. Tous les arguments dont
% le numéro figure en tant que \meta{chiffre} dans la \meta{liste} seront
% optionnels, avec pour valeur par défaut celle donnée par la \meta{valeur}
% correspondante.
%
% Concernant l'usage des commandes, notez que, si les arguments $1$ et $2$
% (par exemple) sont optionnels, vous ne pouvez spécifier de valeur pour
% l'argument $2$ si vous n'en avez pas spécifié pour l'argument $1$. Ce
% comportement est cohérent avec celui de commandes \LaTeX{} existantes, comme
% \cs{makebox}. Il ne provient pas d'une limitation technique mais surtout de
% mon incapacité à imaginer une situation où il est vraiment gênant et une
% syntaxe intelligente pour le contourner.  À ce sujet, observez comment j'ai
% pris soin de séparer les deux arguments optionels par l'argument obligatoire
% dans le définition de \cs{vect} ci-dessus.
%
% Quelques remarques supplémentaires sur la syntaxe de la \meta{liste}, que
% vous pouvez sauter si vous êtes familiers avec la syntaxe fournie par
% \pf{xkeyval}. Vu que les éléments sont séparés par des virgules, si une
% \meta{valeur} doit contenir une virgule, il faut entourer la valeur par des
% accolades pour protéger la virgule. (Cette précaution est également
% indispensable si la \meta{valeur} contient une accolade fermante.) Ne vous
% inquiétez pas, cette parie d'accolade sera retirée ultérieurement.
% D'ailleurs, jusqu'à trois paires d'accolades seront retirées ainsi, et si
% vous voulez vraiment que votre valeur reste entourée d'acollades, il vous
% faudra écrire quelque chose comme~|1={{{{\large blabla}}}}|.
%
% La dernière particularité de la \meta{liste} que vous devez connaître, est
% qu'elle ne doit pas contenir de |\par| (ou de ligne vide). C'est le seul
% point (à ma connaissance) sur lequel les macros d'\pf{xargs} diffèrent des
% macros standard. Cette limitation est liée à un choix dans l'implémentation
% d'\pf{xkeyval}, que j'ai eu un peu la flemme de contourner (en fait, je ne
% suis pas pleinement satisfait de la fiabilité des contournements que je
% connais). Vous pouvez utiliser \cs{endgraf} à la place de \cs{par} en cas de
% besoin. Si cette limitation vous gêne, merci de me le faire savoir.
%
% Parlons maintenant de trois fonctionnalités d'\pf{xargs} qui sont plus ou
% moins cachées mais que j'espère pratiques. La première est que les macros
% sont crées si possible de façon économique : si vous utilisez
% \cs{newcommandx} pour définir un macro que vous auriez pu définir avec
% \cs{newcommand}, \pf{xargs} le détectera et utilisera automatiquement
% \cs{newcommand} à la place. Ainsi, vous n'avez à vous soucier de rien et
% vous pouvez utiliser tout le temps \cs{newcommandx} sans vous poser de
% questions.
%
% La deuxième fonctionnalité est elle aussi transparente, mais comme j'ai pris
% la peine de la coder, il faut bien que j'en parle. Une macro crée par
% \pf{xargs} n'avalera pas les espaces qui la suivent, même si le dernier
% argument est optionel et n'est pas spécifié. C'est un des avantages
% d'\pf{xargs} sur les astuces classiques. Comparez les deux sur l'exemple
% (idiot) suivant :
% \begin{quote}
% |\newcommand\compliment[1]{#1 est gentil\complinterne}|\\
% |\newcommand\complinterne[1][le]{#1}|\\
% |\newcommandx\complimentx[2][2=le]{#1 est gentil#2}|
% \end{quote}
% \newcommand\compliment[1]{#1 est gentil\complinterne}
% \newcommand\complinterne[1][le]{#1}
% \newcommandx\complimentx[2][2=le]{#1 est gentil#2}
% \begin{center}\begin{tabular}{ll}
% |\compliment{Clothilde} et\ldots| & 
% \compliment{Clothilde} et\ldots   \\ 
% |\complimentx{Clothilde} et\ldots| & 
% \complimentx{Clothilde} et\ldots  \\ 
% \end{tabular}\end{center}
% Observez comme l'espace a été avalé de façon indésirable dans le premier
% cas.
%
% Enfin, les macros d'\pf{xargs} essayent de se comporter en tous points comme
% leurs homoloques standard. Il y a deux exceptions : la première est que vous
% ne vous pouvez pas utiliser \cs{par} comme vous voulez, je l'ai dit plus
% haut, et je le regrette. La deuxième réside dans certains comportements de
% \cs{CheckCommandx}. En effet, à l'heure où j'écris ces lignes,
% \cs{CheckCommand} souffre de deux bugs (voir
% \href{http://www.latex-project.org/cgi-bin/ltxbugs2html?pr=latex/3971}
% {PR/3971}) que j'espère avoir évités dans \cs{CheckCommandx}.
% \bigskip
%
% \begin{quote}
% Vous savez maintenant tout ce qu'il y a à savoir sur l'utilisation de
% \pf{xargs}. Si vous souhaitez vous pencher sur son implémentation, il vous
% faudra lire les commentaires en anglais car je n'ai pas eu le courage de
% commenter mon code en deux langues.
% \end{quote}
%
% \begin{center}\large
% C'est tout pour cette fois ! \\
% Amusez-vous bien avec \LaTeX{} !
% \end{center}
%
% \else
%
% The \pf{xargs} package defines an extended variant for every \LaTeX{} macro
% related to macro definition. \pf{xargs}'s macro are named after their
% \LaTeX{} couterparts, just adding an |x| at end, e.g. \cs{newcommandx},
% \cs{renewcommandx} or \cs{newenvironmentx}. Since they all share the same
% syntax (closely ressembling \cs{newcommand}'s one), I will only explain with
% \cs{newcommandx}.
%
% Let's begin with an example. After the following definitions,
% \begin{center}
% |\newcommandx*\vect[3][1=1, 3=n]{(#2_{#1},\ldots,#2_{#3})}|
% \end{center}
% \newcommandx*\vect[3][1=1, 3=n]{(#2_{#1},\ldots,#2_{#3})} 
% you can use \cs{vect} like this:
% \begin{center}
% \begin{tabular}{ll}
% |$\vect{x}$| & $\vect{x}$ \\
% |$\vect[0]{y}$| & $\vect[0]{y}$ \\
% |$\vect{z}[m]$| & $\vect{z}[m]$ \\
% |$\vect[0]{t}[m]$| & $\vect[0]{t}[m]$ \\
% \end{tabular}
% \end{center}
%
% You surely understood \cs{vect} is now a macro with 3 arguments, the first
% and third being optional. They both have their own default value (resp.
% |1| and |n|). You maybe noticed how \cs{newcommandx}'s syntax closely
% ressembles \cs{newcommand}'s syntax: the only difference is that, instead of
% the default value of the only optional argument, you have to specifiy the
% number of the optional arguments, followed by a = and their default value.
%
% Now let's have a closer look at \cs{newcommandx}'s syntax, shared by all
% other \pf{xargs} commands. (While dealing with details, here is the complete
% list of those: \cs{newcommandx} and \cs{renewcommandx} for simple macros,
% \cs{providecommandx} to make sure a macro exists, \cs{DeclareRobustCommandx}
% to (re)define a robust macro, \cs{CheckCommandx} to check if a macro has the
% correct meaning, \cs{newenvironmentx} and \cs{renewenvironmentx} for
% environments.)
%
% \begin{center}
% \cs{newcommandx} \meta{|*|} \marg{command} \oarg{number} \oarg{list}
% \marg{definition}
% \end{center}
%
% Everything here is the same as usual \cs{newcommand} syntax, except
% \meta{list}. Let's recall this briefly. The optional |*| make \LaTeX{}
% define a ``short'' macro, that is a macro that won't accept a paragraph
% break (\cs{par} or an empty line) inside its argument, otherwise the macro
% will be long.  \meta{command} is any control sequence, and can but need not
% be enclosed in braces, as you like. The \meta{number} specifies how many
% arguments your macro will take (including optional ones): It should be a
% non-negative integer, and at most $9$. The macro's \meta{definition} is a
% balanced text, where every |#| sign must be followed with a number, thus
% representing an argument, or with another |#| sign. The two arguments
% \meta{number} and \meta{list} are optionals.
%
% Now comes the new and funny part. \meta{list} is a coma-separated list of
% element \meta{digit}=\meta{value}. Here, \meta{digit} should be non-zero,
% and at most \meta{number} (the total number of arguments). The \meta{value}
% is any balanced text, and can be empty. If so, the |=| sign becomes
% optional: You only need to write \meta{digit} if you want the \meta{digit}th
% argument to be optional, with empty default value. Of course, every argument
% whose number is a \meta{digit} in the \meta{list} becomes optional, with
% \meta{value} as its default value.
%
% While using a macro with many optional arguments, keep in mind the following
% fact. If arguments, say $1$ and $2$, are optional, then if you specify a
% value for only one optional argument, it will be used for argument $1$, and
% argument $2$ will be considered non-specified (thus its default value will
% be used).  This behaviour is consistent with existing \LaTeX{}'s command,
% like \cs{makebox}. It isn't a technical limitation, I just couldn't imagine
% a better way to do. By the way, please notice the way I separated the two
% optional arguments from the example above in order to be able to use them
% independantly.
%
% If you are not very familiar with some aspects of the syntax provided by the
% \pf{xkeyval} package, you may be interested in the following remarks about
% the syntax of \meta{list}. Since \meta{list} is coma-separated, if you want
% to use a coma inside a \meta{value}, you need to enclose it (either the coma
% or the whole \meta{value}) in braces. The same applies if you want to use a
% closing square bracket inside the \meta{list}. Don't worry about those
% unwanted braces, they will be removed later. Actually, \pf{xkeyval} removes
% up to $3$ braces set: If you really want braces around a value, you need to
% type something like |1={{{{\large stuff}}}}|.
%
% The last thing you (maybe) need to know about \meta{list} is a little
% limitation of \pf{xargs}, inherited from \pf{xkeyval}, which I didn't
% managed to work around (actually, I know a way to do it, but it fails in
% rare cases involving \cs{let}ing an active character equal to a brace, so I
% decided not to include it). So what is this problem? It's just you cannot
% use \cs{par} (or an empty line) in the \meta{list}. If you need a paragraph
% break in a \meta{value}, try \cs{endgraf}. If this issue really bothers you,
% please let me know.
%
% There's only three features of \pf{xargs} not yet discussed. Since they are
% all ``good'' features, you may not need to read the end of the
% documentation, but since I made the effort to implement it, I want to talk
% about it. First one is that macros are made in a minimalistic way: If you
% use \cs{newcommandx} to create a macro you could have made with
% \cs{newcommand}, \pf{xargs} will notice and use \cs{newcommand} internally.
% So, you can allways use \cs{newcommandx} without bothering.
%
% Second feature consist in avoiding a possible problem with spaces after a
% macro whose last argument is optional. If defined in a naive way, such
% macros would gobble spaces after them when the optional argument is not
% specified, but macros created with \pf{xargs} don't, so you don't need to
% take any special care about spaces.
%
% Last, \pf{xargs} macros try to behave exactly as standard \LaTeX{} macros
% do. As far as I know, there are only two exceptions. I allready mentionned
% the first, which is the problem with \cs{par} in default value, due to
% \pf{xkeyval}.  The other one is that, right now, the current implementation
% of \cs{CheckCommand} has some problems (see
% \href{http://www.latex-project.org/cgi-bin/ltxbugs2html?pr=latex/3971}
% {PR/3971}). I tried not to reproduce them in \cs{CheckCommandx}.
%
% \fi
%
% \StopEventually{}
%
%         \section{Implementation}
%
% \begingroup \def\leaders#1#2{}
% \secttoc[n]
% \endgroup
%
% If you are familiar with the way \LaTeXe{} manages macros with an optional
% argument, then you will probably not be surprised by the \pf{xargs} way.
% Indeed, with \LaTeXe{}, a command \cs{foo} defined with, say
% |\newcommand*\foo[2][bar]{baz}| is implemented as the pair:
% \begin{quote}
% |\foo=macro:->\@protected@testopt\foo\\foo{bar}| \\
% |\\foo=macro:[#1]#2->baz|
% \end{quote}
% With \pf{xargs}'s \cs{newcommandx}, a macro \cs{vect} as above is
% implemented as:
% \begin{quote}
% |\vect=macro:->\@protected@testopt@xargs\vect\\vect|\\
% \hspace*{1em}|{\xargs@test@opt{0},\xargs@put@arg,\xargs@test@opt{n},}|\\
% |\\vect=macro:[#1]#2[#3]->(#2_{#1},\ldots ,#2_{#3})|
% \end{quote}
%
% This is very similar: the ``real'' macro is the one whose name begins with a
% \cs{} and the macro called by the user just checks the protection context
% and collects the arguments for the internal macro, using the default value
% if none is given for the optional argument(s). However, the analogy ends
% here, since in ``normal'' \LaTeX{} there is only one optional argument, but
% \pf{xargs} commands need more information about optional arguments,
% namely their position, and not only the default values.
%
% This information is stored as a coma-separated list of ``actions'', each
% action consisting of either the single command \cs{xargs@put@arg}, which
% denotes a mandatory argument and makes \LaTeX{} grab it and add it to the
% list of arguments to be passed to the internal macro, or \cs{xargs@test@opt}
% with argument the default value, which denotes an optional argument. In the
% later case, the presence of the optional argument is checked in a way
% slightly differing from \LaTeXe's \cs{@ifnextchar}, then the relevant value
% added to the arguments list.
%
% \subsection{Parser}
%
% All this argument grabing job is done with a loop that read and executes
% each action from the originating list, and concurrently builds an argument
% list such as |[0]{x}[m]| to be passed to |\\vect| for example. The first
% part of the code consists of those macros used for the argument grabbing and
% execution of internal command process.
%
% \medskip
% First, load the \pf{xkeyval} package for it's nice key=value syntax.
%    \begin{macrocode}
\RequirePackage{xkeyval}
%    \end{macrocode}
%
% \begin{macro}{\xargs@max}
% \begin{macro}{\xargs@temp}
% \begin{macro}{\xargs@toksa}
% \begin{macro}{\xargs@toksb}
% Then allocate a few registers and make sure the name of our private scratch
% macro is free for use. Note that for certain uses, we really need a
% \cs{toks} register because the string used can possibly contain |#|
% characters.  Sometimes I also use a \cs{toks} register instead of a macro
% just for ease of use (writing less \cs{expandafter}s).
%    \begin{macrocode}
\@ifdefinable\xargs@max{\newcount\xargs@max}
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@temp\relax
\@ifdefinable\xargs@toksa{\newtoks\xargs@toksa}
\@ifdefinable\xargs@toksb{\newtoks\xargs@toksb}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}{\@protected@testop@xargs}
% This first macro closely resembles kernel's \cs{@protected@testopt}
% (similarity in their names is intentional, see \cs{CheckCommandx}). It just
% checks the protection context and call the real argument grabbing macro.
%    \begin{macrocode}
\newcommand*\@protected@testopt@xargs[1]{%
  \ifx\protect\@typeset@protect
    \expandafter\xargs@read
  \else
    \@x@protect#1%
  \fi}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\xargs@read}
% Initiate the loop. \cs{xargs@toksa} will become the call to the internal macro
% with all arguments, \cs{xargs@toksb} contains the actions list for arguments
% grabbing. 
%    \begin{macrocode}
\newcommand*\xargs@read[2]{%
  \begingroup
  \xargs@toksa{#1}%
  \xargs@toksb{#2}%
  \xargs@continue}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\xargs@continue}
% \begin{macro}{\xargs@pick@next}
% Each iteration of the loop consist of two steps: pick the next action (and
% remove it from the list), and execute it. When there is no more action in
% the list, it means the arguments grabbing stage is over, and it's time to
% execute the internal macro by expanding the contents of \cs{xargs@toksa}.
%    \begin{macrocode}
\newcommand\xargs@continue{%
  \expandafter\xargs@pick@next\the\xargs@toksb,\@nil
  \xargs@temp}
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@pick@next{%
  \def\xargs@pick@next#1,#2\@nil{%
    \def\xargs@temp{#1}%
    \xargs@toksb{#2}%
    \ifx\xargs@temp\empty
      \def\xargs@temp{\expandafter\endgroup\the\xargs@toksa}%
    \fi}}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@set@defflag[1]{%
  \def\xargs@default@flag{#1}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\xargs@put@arg}
% \begin{macro}{\xargs@test@opt}
% \begin{macro}{\xargs@put@opt}
% Now have a look at the argument grabbing macros. The first one,
% \cs{xargs@put@arg}, just reads an undelimited argument in the input stack
% and add it to the arguments list. \cs{xargs@testopt} checks if the next
% non-space token is a square bracket to decide if it have to read an argument
% from the input or use the default value, and takes care to enclose it in
% square brackets.
%    \begin{macrocode}
\newcommand\xargs@put@arg[1]{%
  \xargs@toksa\expandafter{\the\xargs@toksa{#1}}%
  \xargs@continue}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@test@opt[1]{%
  \xargs@ifnextchar[%]
    {\xargs@grab@opt{#1}}%
    {\xargs@put@opt{#1}}}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand\xargs@put@opt[1]{%
    \xargs@toksa\expandafter{\the\xargs@toksa[{#1}]}%
  \xargs@continue}
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@grab@opt{%
  \long\def\xargs@grab@opt#1[#2]{%
    \toks@{#2}\edef\xargs@temp{\the\toks@}%
    \ifx\xargs@temp\xargs@default@flag 
      \expandafter\@firstoftwo
    \else
      \expandafter\@secondoftwo
    \fi{%
      \xargs@put@opt{#1}%
      }{%
      \xargs@put@opt{#2}}}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}{\xargs@ifnextchar}
% \begin{macro}{\xargs@ifnch}
% \begin{macro}{\xargs@xifnch}
% You probably noticed that \cs{xargs@testopt} doesn't use kernel's
% \cs{@ifnextchar}. The reason is, I don't want macros to gobble space if
% their last argument is optional and not specified. Indeed, it would be
% strange to have spaces after |\vect[0]{x}| gobbled. So the modified version
% of \cs{@ifnextchar} below works like kernel's one, except that it remembers
% how many spaces it gobbles and restitutes them in case the next non-space
% character isn't a match.
%    \begin{macrocode}
\newcommand\xargs@ifnextchar[3]{%
  \let\xargs@temp\empty
  \let\reserved@d=#1%
  \def\reserved@a{#2}%
  \def\reserved@b{#3}%
  \futurelet\@let@token\xargs@ifnch}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand\xargs@ifnch{%
  \ifx\@let@token\@sptoken
    \edef\xargs@temp{\xargs@temp\space}%
    \let\reserved@c\xargs@xifnch
  \else
    \ifx\@let@token\reserved@d
      \let\reserved@c\reserved@a
    \else
      \def\reserved@c{\expandafter\reserved@b\xargs@temp}%
    \fi
  \fi
  \reserved@c}
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@xifnch{%
  \expandafter\def\expandafter\xargs@xifnch\space{%
    \futurelet\@let@token\xargs@ifnch}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% 
% \subsection{Keys}
%
% Okay, we are done with the execution related macros. Now let's start with
% stuff for the definition of macros. In this part we use \pf{xkeyval}.
% Let's start with the particular keys for options addprefix and default. Like
% all \pf{xargs} key, we use prefix |xargs| and familly |key|. The addprefix
% key can be used many times : each value is appended at the end of the
% current prefix. Actually, we also construct a ``short'' prefix (without any
% \cs{long}), for the external macro. We define them globally, since key
% processing will happen inside a group, and the definition outside.
%    \begin{macrocode}
\@ifdefinable\xargs@key@prefix{%
  \define@key[xargs]{key}{addprefix}[]{%
    \global\expandafter\def\expandafter\xargs@prefix\expandafter{%
      \xargs@prefix#1}%
    \xargs@makeshort#1\long\@nil}}
%    \end{macrocode}
% The \cs{long} tokens are removed from the prefix in a fast and easy way,
% assuming the input is a correct prefix. (It will crash e.g. if the input
% contains an undefined CS or braces, but this will make all crash later
% anyway. By the way, we also assume the prefix contains no macro parameter
% token\ldots)
%    \begin{macrocode}
\@ifdefinable\xargs@makeshort{%
  \def\xargs@makeshort#1\long#2{%
    \expandafter\gdef\expandafter\xargs@shortpref\expandafter{%
      \xargs@shortpref#1}%
    \ifx#2\@nil \else
      \expandafter\xargs@makeshort\expandafter#2%
    \fi}}
%    \end{macrocode}
% The initial prefixes will be fixed by \cs{newcommandx} and its friends when
% they check the star: empty in the stared version, \cs{long} otherwise. For
% this, they use \pf{xargs}'s variant or \cs{@star@or@long}: 
%    \begin{macrocode}
\newcommand\xargs@star@or@long[1]{%
  \global\let\xargs@shortpref\@empty
  \@ifstar{\gdef\xargs@prefix{}#1}{\gdef\xargs@prefix{\long}#1}}
%    \end{macrocode}
%
% Now, another particular key is the |usedefault| key. When used, it just sets
% \cs{xargs@default@flag} and the corresponding boolean. Later on, this
% will be used to possibly introduce a \cs{xargs@set@default} action at
% the beginning of the actions list. 
%    \begin{macrocode}
\define@key[xargs]{key}{usedefault}[]{%
  \xargs@toksa{#1}\edef\xargs@default@flag{\the\xargs@toksa}}
%    \end{macrocode}
% 
% 
% Let's continue with the more important keys. The idea is to collect through
% \pf{xkeyval} at most 9 actions numbered 1 to \cs{xargs@max} (the total
% number of arguments) of the type seen above, then structure them in a
% coma-separated list for use in the definition of the user macro. Special
% care is taken to define simpler macros in the two special cases where all
% arguments, possibly except the first one, are mandatory (standard \LaTeXe{}
% cases).
%
% \begin{macro}{\@namenewc}      \begin{macro}{\xargs@action@1}
% \begin{macro}{\xargs@action@2} \begin{macro}{\xargs@action@3}
% \begin{macro}{\xargs@action@4} \begin{macro}{\xargs@action@5}
% \begin{macro}{\xargs@action@6} \begin{macro}{\xargs@action@7}
% \begin{macro}{\xargs@action@8} \begin{macro}{\xargs@action@9}
% So our first task is to define container macros for the at most nine
% actions which represent arguments parsing, with default value
% \cs{xargs@put@arg} since every argument is mandatory unless specified.
%    \begin{macrocode}
\providecommand\@namenewc[1]{%
  \expandafter\newcommand\csname #1\endcsname}
%    \end{macrocode}
%    \begin{macrocode}
\@namenewc{xargs@action@1}{\xargs@put@arg}
\@namenewc{xargs@action@2}{\xargs@put@arg}
\@namenewc{xargs@action@3}{\xargs@put@arg}
\@namenewc{xargs@action@4}{\xargs@put@arg}
\@namenewc{xargs@action@5}{\xargs@put@arg}
\@namenewc{xargs@action@6}{\xargs@put@arg}
\@namenewc{xargs@action@7}{\xargs@put@arg}
\@namenewc{xargs@action@8}{\xargs@put@arg}
\@namenewc{xargs@action@9}{\xargs@put@arg}
%    \end{macrocode}
% \end{macro} \end{macro}
% \end{macro} \end{macro}
% \end{macro} \end{macro}
% \end{macro} \end{macro}
% \end{macro} \end{macro}
% \begin{macro}{\xargs@def@key}
% The next macro will define the keys for us. Its first argument is the key's
% number. The second argument will be discussed later.
%    \begin{macrocode}
\newcommand*\xargs@def@key[2]{%
  \expandafter\@ifdefinable\csname xargs@key@#1\endcsname{%
    \define@key[xargs]{key}{#1}[]{%
%    \end{macrocode}
% The first thing do to, before setting any action, is to check wether this
% key can be used for this command, and complain if not.
%    \begin{macrocode}
      \ifnum\xargs@max<#1
        \PackageError{xargs}{%
          Illegal argument label in\MessageBreak
          optional arguments description%
          }{%
          You are trying to make optional an argument whose label (#1)
          \MessageBreak is higher than the total number (\the\xargs@max)
          of parameters. \MessageBreak This can't be done and your 
          demand will be ignored.}%
      \else
%    \end{macrocode}
% If the key number is correct, it may be that the user is trying to use it
% twice for the same command. Since it's probably a mistake, issue a warning
% in such case.
%    \begin{macrocode}
        \expandafter\expandafter\expandafter
        \ifx\csname xargs@action@#1\endcsname\xargs@put@arg \else
          \PackageWarning{xargs}{%
            Argument #1 was allready given a default value.\MessageBreak
            Previous value will be overriden.\MessageBreak}%
        \fi
%    \end{macrocode}
% If everything looks okay, define the action to be \cs{xargs@test@opt} with
% the given value, and execute the (for now) mysterious second argument.
%    \begin{macrocode}
        \@namedef{xargs@action@#1}{\xargs@test@opt{##1}}%
        #2%
      \fi}}}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\ifxargs@firstopt@}
% \begin{macro}{\ifxargs@otheropt@}
% \begin{macro}{\xargs@key@1}
% \begin{macro}{\xargs@key@2} \begin{macro}{\xargs@key@3}
% \begin{macro}{\xargs@key@4} \begin{macro}{\xargs@key@5}
% \begin{macro}{\xargs@key@6} \begin{macro}{\xargs@key@7}
% \begin{macro}{\xargs@key@8} \begin{macro}{\xargs@key@9}
% The second argument just consist in setting the value for some \cs{if} wich
% will keep track of the existence of an optional argument other than the
% first one, and the of the possibly otpional nature of the first. Such
% information will be usefull when we will have to decide if we use the
% \LaTeXe{} standard way or \pf{xargs} custom one to define the macro.
%    \begin{macrocode}
\newif\ifxargs@firstopt@
\newif\ifxargs@otheropt@
%    \end{macrocode}
% Now actually define the keys. 
%    \begin{macrocode}
\xargs@def@key1\xargs@firstopt@true
\xargs@def@key2\xargs@otheropt@true \xargs@def@key3\xargs@otheropt@true
\xargs@def@key4\xargs@otheropt@true \xargs@def@key5\xargs@otheropt@true
\xargs@def@key6\xargs@otheropt@true \xargs@def@key7\xargs@otheropt@true
\xargs@def@key8\xargs@otheropt@true \xargs@def@key9\xargs@otheropt@true
%    \end{macrocode}
% \end{macro} \end{macro} \end{macro}
% \end{macro} \end{macro} \end{macro}
% \end{macro} \end{macro} \end{macro}
% \end{macro} \end{macro}
% \begin{macro}{\xargs@setkeys}
% \begin{macro}{\xargs@check@keys}
% We set the keys with the starred version of \cs{setkeys}, so we can check if
% there were some strange keys we cannot handle, and issue a meaningfull
% warning if there are some.
%    \begin{macrocode}
\newcommand\xargs@setkeys[1]{%
  \setkeys*[xargs]{key}{#1}%
  \xargs@check@keys}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand\xargs@check@keys{%
  \ifx\XKV@rm\empty \else
    \xargs@toksa\expandafter{\XKV@rm}%
    \PackageError{xargs}{%
      Illegal argument label in\MessageBreak
      optional arguments description%
      }{%
      You can only use non-zero digits as argument labels.\MessageBreak
      You wrote: "\the\xargs@toksa".\MessageBreak
      I can't understand this and I'm going to ignore it.}%
  \fi}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \subsection{Definition}
%
% \begin{macro}{\xargs@add@args}
% Now our goal is to build two lists from our up to nine actions macros. The
% first is the coma-separated list of actions allready discussed. The second
% is the parameter text for use  in the definition on the internal macro, for
% example |[#1]#2[#3]|. The next macro takes the content of a
% \cs{xargs@action@X} macro for argument and adds the corresponding items to
% this lists. It checks if the first token of its parameter is
% \cs{xargs@testopt} in order to know if the |#n| has to be enclosed in square
% brackets.
%    \begin{macrocode}
\newcommand\xargs@add@args[1]{%
  \xargs@toksa\expandafter{\the\xargs@toksa #1,}%
  \expandafter
  \ifx\@car#1\@nil\xargs@put@arg
    \xargs@toksb\expandafter\expandafter\expandafter{%
      \the\expandafter\xargs@toksb\expandafter##\the\count@}%
  \else
    \xargs@toksb\expandafter\expandafter\expandafter{%
      \the\expandafter\xargs@toksb\expandafter
      [\expandafter##\the\count@]}%
  \fi}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\xargs@process@keys}
% Here comes the main input processing macro, which prepares the information
% needed to define the final macro, and expands it to the defining macro.
%    \begin{macrocode}
\@ifdefinable\xargs@process@keys{%
  \long\def\xargs@process@keys#1[#2]{%
%    \end{macrocode}
% Some initialisations. We work inside a group so that the default values for
% the \cs{xargs@action@X} macros and the \cs{xargs@XXXopt@} be automatically
% restored for the next time.
%    \begin{macrocode}
    \begingroup
    \xargs@setkeys{#2}%
    \xargs@toksa{}\xargs@toksb{}%
%    \end{macrocode}
% Now the |usedefault| part.
%    \begin{macrocode}
    \@ifundefined{xargs@default@flag}{}{%
      \xargs@toksa\expandafter{%
        \expandafter\xargs@set@defflag\expandafter{\xargs@default@flag}}}
%    \end{macrocode}
% Then the main loop actually builds up the two lists in the correct order.
%    \begin{macrocode}
    \count@\z@
    \@whilenum\xargs@max>\count@ \do{%
      \advance\count@\@ne
      \expandafter\expandafter\expandafter\xargs@add@args
      \expandafter\expandafter\expandafter{%
        \csname xargs@action@\the\count@\endcsname}}%
%    \end{macrocode}
% Then we need to  address a special case: if only the first argument is
% optional, we use \LaTeXe's standard \cs{newcommand} construct, and we dont
% need an actions list like the one just build, but only the default value for
% the first argument. In this case, we extract this value from
% \cs{xargs@action@1} by expanding it three times with a modified
% \cs{xargs@testopt}.
%    \begin{macrocode}
    \ifxargs@otheropt@ \else
      \ifxargs@firstopt@
        \let\xargs@test@opt\@firstofone
        \xargs@toksa\expandafter\expandafter\expandafter
        \expandafter\expandafter\expandafter\expandafter{%
          \csname xargs@action@1\endcsname}%
      \fi
    \fi
%    \end{macrocode}
% Before we do the definitions, remember to execute \cs{xargs@drc@hook},
% since the next macros will only define the internal macro(s) with a
% \cs{DeclareRobustCommandx}, and the hook defines the user macro, with
% the correct prefix now.
%    \begin{macrocode}
    \xargs@drc@hook
%    \end{macrocode}
% Finally expand the stuff to the next macro and, while we're at it,
% choose the next macro : depending of the existence and place of an
% optional argument, use \LaTeX's or \pf{xargs}'s way. In the \LaTeX{}
% case, however, we don't use \cs{@argdef} or \cs{xargdef} since we want
% to be able to use a prefix (and we have more work done allready, too).
%    \begin{macrocode}
    \edef\xargs@temp{%
      \ifxargs@otheropt@ \noexpand\xargs@xargsdef \else
        \ifxargs@firstopt@ \noexpand\xargs@xargdef \else 
          \noexpand\xargs@argdef 
      \fi\fi
      \noexpand#1%
      \expandafter\noexpand\csname\string#1\endcsname
      {\the\xargs@toksa}{\the\xargs@toksb}}%
%    \end{macrocode}
% Now we can close the group and forget all about key values, etc. Time
% to conclude and actually define the macro. (The only thing not passed
% as an argument is the prefix, which is globally set.)
%    \begin{macrocode}
    \expandafter\endgroup
    \xargs@temp}}
%    \end{macrocode}
% \end{macro}
%    \begin{macrocode}
\newcommand\xargs@argdef[5]{%
  \@ifdefinable#1{%
    \xargs@prefix\def#1#4{#5}}}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand\xargs@xargdef[5]{%
  \@ifdefinable#1{%
    \xargs@shortpref\def#1{\@protected@testopt#1#2{#3}}%
    \xargs@prefix\def#2#4{#5}}}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand\xargs@xargsdef[5]{%
  \@ifdefinable#1{%
    \xargs@shortpref\def#1{\@protected@testopt@xargs#1#2{#3}}%
    \xargs@prefix\def#2#4{#5}}}
%    \end{macrocode}
%
% \subsection{User macros}
%
% \begin{macro}{\newcommandx}
% \begin{macro}{\xargs@newc}
% All the internal macros are ready. It's time to define the user commands,
% beginning with \cs{newcommandx}. Like its standard version, it just checks
% the star and call the next macro wich grabs the number of arguments.
%    \begin{macrocode}
\newcommand\newcommandx{%
  \xargs@star@or@long\xargs@newc}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@newc[1]{%
  \@testopt{\xargs@set@max{#1}}{0}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\xargs@set@max}
% Set the value of \cs{xargs@max}. If no optional arguments description
% follows, simply call \cs{argdef} because all the complicated stuff is
% useless here.
%    \begin{macrocode}
\@ifdefinable\xargs@set@max{%
  \def\xargs@set@max#1[#2]{%
    \kernel@ifnextchar[%]
      {\xargs@max=#2 \xargs@check@max{#1}}%
      {\@argdef#1[#2]}}}
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\xargs@check@max}
% To avoid possible problems later, check right now that \cs{xargs@max} value
% is valid. If not, warn the user and treat this value as zero. Then begin the
% key processing.
%    \begin{macrocode}
\newcommand\xargs@check@max{%
  \ifcase\xargs@max \or\or\or\or\or\or\or\or\or\else
    \PackageError{xargs}{Illegal number, treated as zero}{The total
      number of arguments must be in the 0..9 range.\MessageBreak
      Since your value is illegal, i'm going to use 0 instead.}
    \xargs@max0
  \fi
  \xargs@process@keys}
%    \end{macrocode}
% \end{macro}
% The other macros (\cs{renewcommand} etc) closely resemble their kernel
% couterpart, since they are mostly wrappers around some call to
% \cs{xargs@newc}. There is however an exception, \cs{CheckCommand}, which I
% will treat first. Here my way differs from the kernel's one, since current
% implemetation of \cs{CheckCommand} in the kernel suffers from two bugs (see
% \href{http://www.latex-project.org/cgi-bin/ltxbugs2html?pr=latex/3971}
% {PR/3971}).
% \begin{macro}{\CheckCommandx}
% We begin as usual detecting the possible star.
%    \begin{macrocode}
\@ifdefinable\CheckCommandx{%
  \def\CheckCommandx{%
    \xargs@star@or@long\xargs@CheckC}}
\@onlypreamble\CheckCommandx
%    \end{macrocode}
% \end{macro}
% \begin{macro}{\xargs@CheckC}
% \begin{macro}{\xargs@check@a}
% \begin{macro}{\xargs@check@b}
% First, we don't use the |#2#| trick from the kernel, since it can fail if
% there are braces in the default values. Instead, we follow the argument
% grabing method used for \cs{new@environment}, ie calling
% \cs{kernel@ifnextchar} explicitly.
%    \begin{macrocode}
\@ifdefinable\xargs@CheckC{%
  \def\xargs@CheckC#1{%
    \@testopt{\xargs@check@a#1}0}}
\@onlypreamble\xargs@CheckC
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@check@a{%
  \def\xargs@check@a#1[#2]{%
    \kernel@ifnextchar[%]
      {\xargs@check@b#1[#2]}%
      {\xargs@check@c#1{[#2]}}}}
\@onlypreamble\xargs@check@a
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@chech@b{%
  \def\xargs@check@b#1[#2][#3]{%
    \xargs@check@c{#1}{[#2][{#3}]}}}
\@onlypreamble\xargs@check@b
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}{\xargs@CheckC}
% Here comes the major difference with the kernel version. If |\\reserved@a| is
% defined, we not only check that it is equal to |\\foo| (assuming \cs{foo} is
% the macro being tested), we also check that \cs{foo} makes something
% sensible, with \cs{xargs@check@d}.
%    \begin{macrocode}
\newcommand\xargs@check@c[3]{%
  \xargs@toksa{#1}%
  \expandafter\let\csname\string\reserved@a\endcsname\relax
  \xargs@renewc\reserved@a#2{#3}%
  \@ifundefined{\string\reserved@a}{%
    \ifx#1\reserved@a \else
      \xargs@check@complain
    \fi
    }{%
    \expandafter
    \ifx\csname\string#1\expandafter\endcsname
        \csname\string\reserved@a\endcsname
      \xargs@check@d
    \else
      \xargs@check@complain
    \fi}}
\@onlypreamble\xargs@check@c
%    \end{macrocode}
% \end{macro}
% So, what do we want \cs{foo} to do? If |\\foo| is defined, \cs{foo} should
% begin with one of the followings:
% \begin{quote}
% |\@protected@testopt \foo \\foo| \\
% |\@protected@testopt@xargs \foo \\foo|
% \end{quote}
% Since I'm to lazy to really check this, the \cs{xargs@check@d} macro only
% checks if the \cs{meaning} of \cs{foo} begins with \cs{@protected@test@opt}
% (without a space after it). It does this using a macro with delimited
% argument. Here are preliminaries to this definition: We need to have this
% string in \cs{catcode} 12 tokens.
%    \begin{macrocode}
\def\xargs@temp{\@protected@testopt}
\expandafter\xargs@toksa\expandafter{\meaning\xargs@temp}
\def\xargs@temp#1 {\def\xargs@temp{#1}}
\expandafter\xargs@temp\the\xargs@toksa
%    \end{macrocode}
% \begin{macro}{\xargs@check@d}
% \begin{macro}{\xargs@check@e}
% Now, \cs{xargs@check@c} just pass the \cs{meaning} of the command \cs{foo}
% being checked to the allready mentionned macro with delimited arguments,
% which will check if its first argument is empty (ie, if \cs{foo}'s
% \cs{meaning} starts with what we want) and complain otherwise.
%    \begin{macrocode}
\@ifdefinable\xargs@check@d{%
  \expandafter\newcommand\expandafter\xargs@check@d\expandafter{%
    \expandafter\expandafter\expandafter\xargs@check@e
    \expandafter\meaning\expandafter\reserved@a\xargs@temp\@nil}}
\@onlypreamble\xargs@check@d
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@check@e{%
  \expandafter\def\expandafter\xargs@check@e
  \expandafter#\expandafter1\xargs@temp#2\@nil{%
    \ifx\empty#1\empty \else
      \xargs@check@complain
    \fi}}
\@onlypreamble\xargs@check@e
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\xargs@check@complain}
% The complaining macro uses the name saved by \cs{xargs@check@c} in
% \cs{xargs@toksa} in order to complain about the correct macro.
%    \begin{macrocode}
\newcommand\xargs@check@complain{%
  \PackageWarningNoLine{xargs}{Command \the\xargs@toksa has changed.
    \MessageBreak Check if current package is valid}}
\@onlypreamble\xargs@check@complain
%    \end{macrocode}
% \end{macro}
% \medskip
%
% From now on, there is absolutely nothing to comment on, since the next
% macros are mainly wrappers around \cs{xargs@newc}, just as kernel's ones are
% wrappers around \cs{new@command}. So the code below is only copy/paste with
% search\&replace from the kernel code.
%
% \begin{macro}{\renewcommandx}
% \begin{macro}{\xargs@renewc}
% The \pf{xargs} version of \cs{renewcommand}, and related internal macro.
%    \begin{macrocode}
\newcommand\renewcommandx{%
  \xargs@star@or@long\xargs@renewc}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@renewc[1]{%
  \begingroup\escapechar\m@ne
    \xdef\@gtempa{{\string#1}}%
  \endgroup
  \expandafter\@ifundefined\@gtempa{%
    \PackageError{xargs}{\noexpand#1undefined}{%
      Try typing \space <return> \space to proceed.\MessageBreak
      If that doesn't work, type \space X <return> \space to quit.}}%
    \relax
  \let\@ifdefinable\@rc@ifdefinable
  \xargs@newc#1}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\providecommandx}
% \begin{macro}{\xargs@providec}
% The \pf{xargs} version of \cs{providecommand}, and related internal macro.
%    \begin{macrocode}
\newcommand\providecommandx{%
  \xargs@star@or@long\xargs@providec}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@providec[1]{%
  \begingroup\escapechar\m@ne
    \xdef\@gtempa{{\string#1}}%
  \endgroup
  \expandafter\@ifundefined\@gtempa
    {\def\reserved@a{\xargs@newc#1}}%
    {\def\reserved@a{\renew@command\reserved@a}}%
  \reserved@a}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\DeclareRobustCommandx}
% \begin{macro}{\xargs@DRC}
% The \pf{xargs} version of \cs{DeclareRobustCommand}, and related internal
% macro.
%    \begin{macrocode}
\newcommand\DeclareRobustCommandx{%
  \xargs@star@or@long\xargs@DRC}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@DRC[1]{%
  \ifx#1\@undefined\else\ifx#1\relax\else
    \PackageInfo{xargs}{Redefining \string#1}%
  \fi\fi
  \edef\reserved@a{\string#1}%
  \def\reserved@b{#1}%
  \edef\reserved@b{\expandafter\strip@prefix\meaning\reserved@b}%
  \edef\xargs@drc@hook{%
    \noexpand\xargs@shortpref\def\noexpand#1{%
      \ifx\reserved@a\reserved@b
        \noexpand\x@protect
        \noexpand#1%
      \fi
      \noexpand\protect
      \expandafter\noexpand\csname
      \expandafter\@gobble\string#1 \endcsname}%
    \expandafter\let\noexpand\xargs@drc@hook\relax}%
  \let\@ifdefinable\@rc@ifdefinable
  \expandafter\xargs@newc\csname
  \expandafter\@gobble\string#1 \endcsname}
\let\xargs@drc@hook\relax
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \begin{macro}{\newenvironment}
% \begin{macro}{\xargs@newenv}
% \begin{macro}{\xargs@newenva}
% \begin{macro}{\xargs@newenvb}
% \begin{macro}{\xargs@new@env}
% The \pf{xargs} version of \cs{newenvironment}, and related internal macros.
%    \begin{macrocode}
\newcommand\newenvironmentx{%
  \xargs@star@or@long\xargs@newenv}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@newenv[1]{%
  \@testopt{\xargs@newenva#1}0}
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@newenva{%
  \def\xargs@newenva#1[#2]{%
    \kernel@ifnextchar[%]
      {\xargs@newenvb#1[#2]}%
      {\xargs@new@env{#1}{[#2]}}}}
%    \end{macrocode}
%    \begin{macrocode}
\@ifdefinable\xargs@newenvb{%
  \def\xargs@newenvb#1[#2][#3]{%
    \xargs@new@env{#1}{[#2][{#3}]}}}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand\xargs@new@env[4]{%
  \@ifundefined{#1}{%
    \expandafter\let\csname#1\expandafter\endcsname
    \csname end#1\endcsname}%
    \relax
  \expandafter\xargs@newc
    \csname #1\endcsname#2{#3}%
  \xargs@shortpref\expandafter\def\csname end#1\endcsname{#4}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \end{macro}
% \begin{macro}{\renewenvironment}
% \begin{macro}{\xargs@renewenv}
% The \pf{xargs} version of \cs{renewenvironment}, and related internal
% macro.
%    \begin{macrocode}
\newcommand\renewenvironmentx{%
  \xargs@star@or@long\xargs@renewenv}
%    \end{macrocode}
%    \begin{macrocode}
\newcommand*\xargs@renewenv[1]{%
  \@ifundefined{#1}{%
    \PackageError{xargs}{\noexpand#1undefined}{%
      Try typing \space <return> \space to proceed.\MessageBreak
      If that doesn't work, type \space X <return> \space to quit.}}%
    \relax
  \expandafter\let\csname#1\endcsname\relax
  \expandafter\let\csname end#1\endcsname\relax
  \xargs@newenv{#1}}
%    \end{macrocode}
% \end{macro}
% \end{macro}
%
% \bigskip
% \begin{center}\Large
% That's all folks!\\
% Happy \TeX ing!
% \end{center}
%
% \Finale
% 
% \iffalse
%</package>
%<*batchfile>
% \fi
% \typeout{**************************************************}
% \typeout{*}
% \typeout{* To finish the installation you have to move the}
% \typeout{* following file into a directory searched by TeX:}
% \typeout{*}
% \typeout{* \space\space\space\space xargs.sty}
% \typeout{*}
% \typeout{* Documentation is in xargs.dvi or xargs.pdf}
% \typeout{*}
% \typeout{* To produce french documentation, run}
% \typeout{* \space\space \space\space (pdf)latex xargs-fr.drv}
% \typeout{*}
% \typeout{* Happy TeXing!}
% \typeout{*}
% \typeout{**************************************************}
% \iffalse
%</batchfile>
% \fi
\endinput