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+% \CheckSum{893}
+% \iffalse
+%<*driver>
+\documentclass{ltxdoc}
+\usepackage{xdoc2}
+
+\makeatletter
+\NewMacroEnvironment{templatetype}{\XD@grab@harmless\relax}{1}%
+   {\MacroFont#1\ \normalfont type}%
+   {\XDMainIndex{\LevelSorted{#1}{\texttt{#1} template type}}}%
+   {{#1}{\texttt{#1} template type}}%
+   {}%
+\NewMacroEnvironment*{template}{%
+   \XD@grab@harmless\relax\XD@grab@harmless\relax
+}{2}%
+   {\XDParToMargin{\MacroFont #1\textnormal{\slash}#2 \normalfont
+       template}}%
+   {\XDMainIndex{
+      \LevelSorted{#1}{\texttt{#1} template type}%
+      \LevelSorted{#2}{\texttt{#2} template}%
+   }}%
+   {{#1/#2}{\texttt{#1}\slash\texttt{#2} template}}%
+   {\def\XD@template@sort{%
+      \LevelSorted{#1}{\texttt{#1} template type}%
+      \LevelSorted{#2}{\texttt{#2} template}%
+   }}%
+\NewMacroEnvironment*{instance}{%
+   \XD@grab@harmless\relax\XD@grab@harmless\relax
+}{2}%
+   {\XDParToMargin{\MacroFont #1\textnormal{\slash}#2 \normalfont
+       instance}}%
+   {\XDMainIndex{
+      \LevelSorted{#1}{\texttt{#1} template type}%
+      \LevelSorted{#2}{\texttt{#2} instance}%
+   }}%
+   {{#1/#2}{\texttt{#1}\slash\texttt{#2} instance}}%
+   {}%
+\NewMacroEnvironment*{collectioninstance}{%
+   \XD@grab@harmless\relax\XD@grab@harmless\relax\XD@grab@harmless\relax
+}{3}%
+   {\XDParToMargin{\MacroFont #2\textnormal{\slash}#3 \normalfont
+      instance (\texttt{#1} collection)}}%
+   {\XDMainIndex{
+      \LevelSorted{#2}{\texttt{#2} template type}%
+      \LevelSorted{#3}{\texttt{#3} instance}%
+      \LevelSorted{#1}{\texttt{#1} collection}%
+   }}%
+   {{#2/#3/#1}%
+    {\texttt{#2}\slash\texttt{#3} instance (\texttt{#1} collection)}}%
+   {}%
+\@namedef{XD@harmless\string\break}{%
+   \toks@=\expandafter{\the\toks@ \protect\nolinebreak[3]}%
+   \XD@harmless@
+}
+\newcommand\keyvalitem[2]{%
+   \item[#1 (#2)%
+      \IndexEntry{\XD@template@sort
+         \LevelSorted{#1}{\textit{#1} keyval (#2)}%
+      }{usage}{\thepage}%
+   ]%
+}
+\newcommand{\xrefoff}{\scan@allowedfalse}
+\newcommand{\xrefon}{\scan@allowedtrue}
+\makeatother
+
+\newenvironment{syntax}{%
+   \let\\=\break
+   \list{}{%
+      \setlength\topsep{\medskipamount}%
+      \setlength\partopsep{0pt}%
+      \setlength\itemsep{0pt plus 1pt}%
+      \setlength\parsep{\itemsep}%
+      \setlength\leftmargin{3em}%
+      \setlength\listparindent{1em}%
+      \setlength\itemindent{-2em}%
+      \setlength\labelwidth{0pt}%
+      \setlength\labelsep{0pt}%
+      \csname @endparpenalty\endcsname=500
+      \def\makelabel##1{\mbox{\meta{##1}${}\longrightarrow{}$}}%
+   }%
+   \addtolength\rightskip{0pt plus 1fil}%
+   \linepenalty=300%
+}{\endlist}
+\newcommand\branch{\({}\mid{}\)\ignorespaces}
+
+\DeclareRobustCommand{\package}[1]{\textsf{#1}}
+\DeclareRobustCommand{\program}[1]{\textsf{#1}}
+\DeclareRobustCommand\LaTeXplus{\LaTeXe$*$}
+
+\DoNotIndex{\addvspace,\@backslashchar,\begin,\begingroup,\bgroup}
+\DoNotIndex{\csname,\DeclareInstance,\DeclareOption}
+\DoNotIndex{\DeclareTemplate,\DeclareTemplateType,\def}
+\DoNotIndex{\DoParameterAssignments,\edef,\egroup,\@eha}
+\DoNotIndex{\@empty,\end,\endcsname,\endgroup,\endinput,\expandafter}
+\DoNotIndex{\@firstofone,\@firstoftwo,\global,\@gobble,\hb@xt@,\hfil}
+\DoNotIndex{\hsize,\hspace,\IfNoValueTF,\@ifpackageloaded}
+\DoNotIndex{\@ifpackagewith,\@ifundefined,\ignorespaces,\@input@}
+\DoNotIndex{\jobname,\leftskip,\let,\MessageBreak,\@namedef,\@ne}
+\DoNotIndex{\NeedsTeXFormat,\newcommand,\nobreak,\@nobreakfalse}
+\DoNotIndex{\nopagebreak,\normalsize,\NoValue,\number,\outer}
+\DoNotIndex{\p@,\PackageError,\PackageInfo,\PackageWarningNoLine}
+\DoNotIndex{\pagestyle,\par,\parfillskip,\parindent,\parskip}
+\DoNotIndex{\@plus,\ProcessOptions,\protect,\protected@edef}
+\DoNotIndex{\providecommand,\ProvidesPackage,\relax,\renewcommand}
+\DoNotIndex{\RequirePackage,\rightskip,\romannumeral,\@secondoftwo}
+\DoNotIndex{\small,\space,\textbf,\thispagestyle,\thr@@,\tw@}
+\DoNotIndex{\vadjust,\vspace,\z@,\z@skip}
+\DoNotIndex{\iffalse,\ifnum,\ifx,\else,\fi} % \fi \fi
+\DoNotIndexBy{@}
+\DoNotIndexBy{DI@}
+
+\CodelineIndex
+\EnableCrossrefs
+\RecordChanges
+\setcounter{IndexColumns}{2}
+\setcounter{StandardModuleDepth}{2}
+
+
+\begin{document}
+\DocInput{docindex.dtx}
+\PrintChanges
+\PrintIndex
+\end{document}
+%</driver>
+% \fi
+% 
+% \title{The \package{docindex} package}
+% \author{Lars Hellstr\"om}
+% \date{8 July 2003}
+% \maketitle
+% 
+% \begin{abstract}
+%   The \package{docindex} package implements template-based formatting 
+%   of indices and lists of changes\slash glossaries. In addition to this, 
+%   the control structures employed also provide for a couple of new 
+%   features, such as automatic collapsing of trivial index levels.
+% \end{abstract}
+% 
+% \tableofcontents
+% 
+% 
+% \section{Introduction}
+% 
+% In automatically generated indices with multi-level entries, such as the 
+% list of changes of a \package{doc} document, it often happens that some 
+% entries are uniquely identified by their primary level sort keys, 
+% although there are sort keys and text for additional levels. If then 
+% the formatting is designed for entries that are uniquely identified 
+% only when their secondary or tertiary sort keys are considered, one 
+% ends up with a couple of entries that look rather peculiar (building 
+% a tree which never branches) and usually take up much more space than 
+% they need to. The remedy for this is of course to make the formatting 
+% smart enough to recognise this situation when it occurs and flexible 
+% enough to format the text is a more suitable manner.
+% 
+% An example of this is that if a document contains the index 
+% entries\footnote{I'm using the default \program{makeindex} 
+% metacharacters in these examples, but the style file provided for 
+% this package actually uses the same metacharacters as those style files 
+% provided by the \package{doc} package---hence the `\package{doc}' 
+% in `\package{docindex}'. }
+% \begin{quote}
+%   |\index{Bernoulli!Jacob}\index{Bernoulli!Johann}|
+% \end{quote}
+% then it is probably reasonable to format this as
+% \begin{quote}
+%   Bernoulli,\\
+%   \vadjust{}\quad Jacob\\
+%   \vadjust{}\quad Johann
+% \end{quote}
+% but if the index entries instead were
+% \begin{quote}
+%   |\index{Jacobi!Carl}\index{Bernoulli!Jacob}|
+% \end{quote}
+% then it is probably better to format this as
+% \begin{quote}
+%   Bernoulli, Jacob\\
+%   Jacobi, Carl
+% \end{quote}
+% than as
+% \begin{quote}
+%   Bernoulli,\\
+%   \vadjust{}\quad Jacob\\
+%   Jacobi,\\
+%   \vadjust{}\quad Carl
+% \end{quote}
+% 
+% The \program{makeindex} program has some features in this direction, 
+% but they only allow dependence on the previous item in the index, not 
+% the next item, which is what you need to know when deciding whether 
+% `Jacob' should go on the same line as `Bernoulli'. Therefore 
+% \package{docindex} pretty much ignores these features in 
+% \program{makeindex} and instead sees to that each command that is to 
+% typeset an index item knows what kind of items were before and after it.
+% 
+% Another reason for writing this package was to try out the template  
+% mechanisms as provided by the \LaTeXplus\ \package{template} 
+% package.\footnote{\LaTeXplus\ is the name of the \LaTeX\ version after 
+% \LaTeXe. Rather than being a completely different kernel\slash format, 
+% \LaTeXplus\ is (will be) implemented as a collection of \LaTeXe\ 
+% packages which replace parts of the kernel. More information and 
+% package code can be found on the \LaTeX-project website~^^A
+% \cite{LaTeX-project}.} My impression is that this experiment turned 
+% out strikingly well. I have always found the more layout-oriented 
+% aspects of \TeX\ programming a bit cumbersome, but the separation of 
+% layout details from control structures that becomes natural when 
+% employing template mechanisms seems to have made it much easier. I'm 
+% not sure why this is so, but it could be as simple as that the layout 
+% settings are no longer diluted in the control structures. In any 
+% case, I would recommend people creating new \LaTeXe\ packages to 
+% employ template mechanisms in at least the initial development 
+% versions of the package, for the following reasons: (i) it reduces the 
+% work of updating the package for \LaTeXplus, (ii) it furthers the 
+% development of \LaTeXplus, and (iii) it might actually become a 
+% better package.
+% 
+% A third reason for writing the \package{docindex} package was to get 
+% the \LaTeX\ document ``back in control'' of how the index is formatted. 
+% Certainly it is the document which has the final say about what 
+% the command in the \texttt{.ind} file actually do, but the traditional 
+% \program{makeindex} style files that are used place severe restrictions 
+% on the formatting of the index simply because they control where the 
+% commands are put. \package{docindex} tries to reduce these 
+% restrictions by making all texts in the index arguments of commands. 
+% Certainly there is a lot more that could be done in this direction---in 
+% particular, the (page) numbers in the index could be coded as a 
+% |\do|-type list rather than as an explicitly comma-separated list as is 
+% done now---but what is in \package{docindex} at the moment seems to 
+% satisfy all my current needs.
+% 
+% 
+% \section{Usage}
+% 
+% \subsection{Straightforward usage}
+% 
+% To make use of the \package{docindex} package in formatting the index 
+% and list of changes of a \package{doc}-type \LaTeX\ document, you must 
+% do the following:
+% \begin{enumerate}
+%   \item Load the \package{docindex} package (or probably 
+%     rather the \package{docidx2e} package---see below).
+%   \item Make sure that the index entries does not use any commands, 
+%     such as |\verb|, that rely on changing catcodes or otherwise 
+%     need to be executed before the entire entry text has been 
+%     tokenized.
+%   \item Generate the \texttt{.ind} and \texttt{.gls} files using 
+%      \texttt{docindex.ist} as style file for \program{make\-index}.
+% \end{enumerate}
+% (Item~2 may seem like a monumental task if one considers what the 
+% indices of \package{doc} documents traditionally looks like---there's 
+% a  |\verb| for every macro name in the index---but it is really not 
+% that bad. \package{docindex} loads the \package{xdoc} package~^^A
+% \cite{xdoc} which redefines \texttt{macro}, the cross-referencing 
+% mechanism, etc.\ so that the index entries generated by these no 
+% longer uses |\verb|. What is left for you to deal with are merely 
+% the possible uses of |\verb| in explicit |\index| or |\SortIndex| 
+% commands.)
+% 
+% What advantages are there then for the normal user in having 
+% \package{docindex} formatting the index and list of changes, as 
+% opposed to using the default mechanisms in the \package{doc} package? 
+% I can only think of two: the index or list of changes may be typeset in 
+% a single column and the same \program{makeindex} style file can be 
+% used for both index and list of changes. Neither advantage is 
+% significant. Instead the advantage of \package{docindex} lies in that 
+% it becomes much simpler to change the formatting, which is rather an 
+% advantage for advanced users which have special needs, and 
+% in particular one can do this without having to supply e.g.\ extra 
+% \program{makeindex} style files.
+% 
+% Another important point is that what you will want to use is probably 
+% not the \LaTeXplus\ \package{docindex} package, but the ``downgraded'' 
+% \LaTeXe\ version \package{docidx2e}, as the former uses the 
+% \package{galley2} package which currently wrecks pretty much all 
+% justification in all existing document classes. \package{docidx2e} 
+% provides the same features as \package{docindex}, but configuring it 
+% is somewhat more cumbersome since \package{template} won't do most of 
+% the coding for you. It is however rather straightforward to convert 
+% a definition using the \package{docindex} package to something which 
+% achieves the same results with the \package{docidx2e} package.
+% 
+% 
+% \subsection{Multiple indices}
+% 
+% The \package{docindex} package makes it comparatively simple to 
+% include several indices in the same document: all one has to do is 
+% use an instance or template of type \texttt{docindex} for each index 
+% one wishes to typeset. The syntax for using such an instance is
+% \begin{quote}
+%   |\UseInstance{docindex}|\marg{instance}\marg{prologue}^^A
+%   \marg{epilogue}
+% \end{quote}
+% The \meta{prologue} and \meta{epilogue} are texts which will be 
+% printed just before and after the index, respectively, and either may 
+% be empty. The text for the index itself is read from another file, 
+% the name and extentsion of which are specified by the instance. The 
+% \texttt{std} template prints the \meta{prologue} and \meta{epilogue} 
+% in one-column mode, whereas the index itself can be printed in one- or 
+% multicolumn mode (the default is three columns).
+% 
+% The \package{doc} commands |\PrintIndex| and |\PrintGlossary| are 
+% redefined to be
+% \begin{quote}
+%   |\UseInstance{docindex}{index}{\index@prologue}{}|
+% \end{quote}
+% and 
+% \begin{quote}
+%   |\UseInstance{docindex}{changes}{\glossary@prologue}{}|
+% \end{quote}
+% respectively. The \texttt{index} and \texttt{changes} instances of 
+% type \texttt{docindex} give the same formatting as the \package{doc} 
+% defaults. (The \package{docidx2e} definitions even use the 
+% \package{doc} package parameters where applicable, but in 
+% \package{docindex} it is much simpler to redefine the instance from 
+% scratch.)
+% 
+% The format of the sorted index files (\texttt{.ind}, \texttt{.gls}, 
+% etc.) that a \texttt{docindex} instance inputs is rather complicated 
+% and I would suggest that the generation of these files is left to the 
+% \program{makeindex} program, but the complete syntax is described in 
+% Subsection~\ref{Ssec:ist}. The syntax of the unsorted index files 
+% (\texttt{.idx}, \texttt{.glo}, etc.) is simpler; there are only a few 
+% things that are different from the index files of the \package{doc} 
+% package.
+% 
+% The foremost difference is that the index entries should begin not 
+% with |\indexentry| or |\glossaryentry|, but with |\docindexentry|. The 
+% \package{xdoc} package provides hooks with which one can change these 
+% texts in entries generated using the |\index| and |\glossary| commands 
+% (as well as higher-level commands built on these, such as the 
+% |\SortIndex| and |\changes| commands) and \package{docindex} will use 
+% these hooks unless it gets passed the \describeoption{oldkeywords}
+% \texttt{oldkeywords} option. If you are creating a third unsorted 
+% index file then you will have to make sure that the command for writing 
+% to that file uses |\docindexentry| in the right place.
+% 
+% The other difference concerns the composite page numbers. The string 
+% which separates the parts of a composite page number is not a 
+% hyphen `|-|', but the string `|\+|'. (The |\+| command is locally 
+% defined for the typesetting of each index by the \texttt{docindex} 
+% template being used, and the default is to typeset a hyphen.) Again 
+% the \package{xdoc} package provides a hook for this, and this hook is 
+% used by \package{docindex} unless it gets passed the 
+% \texttt{oldkeywords} option.
+% 
+% It also deserves to be listed which the metacharacters are that are 
+% the same as in \package{doc} indices. The level separator is `|>|', 
+% the sort~key\slash item~text separator is `|=|', and the quote 
+% character is `|!|'. All other \program{makeindex} metacharacter 
+% parameters have their default values.
+% 
+% 
+% 
+% \subsection{Configuration}
+% 
+% Configuration of the layout provided by the \package{docindex} 
+% package is primarily done by redefining the \texttt{index} and 
+% \texttt{changes} instances of type \texttt{docindex}, since these are 
+% the instances that are used by the |\PrintIndex| and |\PrintChanges| 
+% commands.
+% 
+% The index in the \texttt{source2e.tex} file (the main driver for the 
+% \LaTeXe\ source) differs from the default in three respects: it is set 
+% in two columns rather than three, there is no seperator character 
+% between the parts of a composite page number, and the pagestyle is set 
+% to \texttt{docindex} during the index. This is set up by the 
+% redefinition
+%\begin{verbatim}
+%\DeclareInstance{docindex}{index}{std}{
+%   columns=2, page-compositor={}, pagestyle=docindex
+%}
+%\end{verbatim}
+% (There are however also some changes of parameters related to 
+% linebreaking; more on that in connection to configuration of the 
+% \texttt{changes} instance below.)
+% 
+% Another kind of modification can be found in the \package{tclldoc} 
+% package~\cite{tclldoc}. Here the primary level in the index is used for 
+% names of procedures and variables, whereas the secondary level for the 
+% namespace of the same (the same name may have different definitions 
+% in different namespaces). If there is only one namespace for a given 
+% name then it is probably overkill to format them as two different 
+% index items, but better to join them. This can be achieved through 
+% the redefinition
+%\begin{verbatim}
+%\DeclareInstance{docindex}{index}{std}{%
+%   item1=fixed-r1a, item2=aloneaccept2
+%}%
+%\end{verbatim}
+% An item handled by the \texttt{fixed-r1a} instance (of type 
+% \texttt{indexitem}) always tries to join with the following item but 
+% rejects to join with the preceeding one. An item handled by the 
+% \texttt{aloneaccept2} instance accepts to join with the preceeding 
+% item if neither that nor the following item is a secondary level item. 
+% Thus an item for a name will join with the following item for a 
+% namespace if there is only one such item. As the reader no doubt 
+% realises, this also solves the problem with the Bernoullis that was 
+% described in the introduction.
+% 
+% \pagebreak[1]
+% 
+% As for configuring the list of changes formatting, it is instructive 
+% to start by considering its default definition:
+%\begin{verbatim}
+%\DeclareInstance{docindex}{changes}{std}{
+%   file-extension = gls,
+%   item2 = fixed-r2a-nocomma,
+%   item3 = fixed-a3r,
+%   columns = 2, 
+%   letter-format = ,
+%   letter-skip = 0pt
+%}
+%\end{verbatim}
+% In the list of changes a secondary level item (which contains the name 
+% of the macro or whatever which was changed) is joined with the 
+% following tertiary level item (which details the change that was made). 
+% There are two columns and letter groups are not given any special 
+% formatting.
+% 
+% The definition of \texttt{changes} that would be used for 
+% \texttt{source2e.tex} differs from the above in only one keyval, 
+% namely \textit{body-setup}, but that contains quite a lot of material. 
+% To begin with there is the default |\small| which selects the font. 
+% Then there is a |\makeatletter| which is needed because some |\changes| 
+% entries in the \LaTeX\ sources include commands (e.g.~|\TeX|) that 
+% (when written to file) expand to other commands whose names include the 
+% |@| character. If these are to be tokenized correctly, |@| must be a 
+% letter when the \texttt{.gls} file is being inputted. Last, but not 
+% least, there is a modification of the linebreaking parameters:
+%\begin{verbatim}
+%\UseTemplate{linebreak}{TeX}{
+%\end{verbatim}
+% The file \texttt{source2e.tex} explicitly sets \textit{hbadness} and 
+% \textit{hfuzz} to make \TeX\ shut up about over- and underfull hboxes.
+%\begin{verbatim}
+%   hbadness=10000, hfuzz=\maxdimen,
+%\end{verbatim}
+% In addition to this, there are a couple of parameters that are set by 
+% the \texttt{multicols} environment to values quite different from the 
+% defaults of the \texttt{TeX} template and thus must be set too. Here 
+% they are shown with their default values. The value of 
+% \textit{emergency\-stretch} could probably be increased.
+%\begin{verbatim}
+%   pretolerance=-1, tolerance=9999, emergencystretch=8pt
+%}
+%\end{verbatim}
+% Summing that up, we arrive at the following definition of the
+% \texttt{changes} instance for \texttt{source2e.tex}.
+%\begin{verbatim}
+%\DeclareInstance{docindex}{changes}{std}{
+%   file-extension = gls,
+%   item2 = fixed-r2a-nocomma,
+%   item3 = fixed-a3r,
+%   columns = 2, 
+%   letter-format = ,
+%   letter-skip = 0pt,
+%   body-setup = \small\makeatletter
+%      \UseTemplate{linebreak}{TeX}{
+%         hbadness=10000, hfuzz=\maxdimen,
+%         pretolerance=-1, tolerance=9999, emergencystretch=8pt
+%      }
+%}
+%\end{verbatim}
+% 
+% Another example can be found in the \package{fisource} 
+% package\footnote{It should probably rather be made a document class, 
+% but I haven't found it that necessary to change that aspect of it.}^^A
+% ~(v\,2.10 or later), which sets up formatting for the \program{fontinst} 
+% source. There the list of changes should be set in one column, with 
+% items from the tertiary level being joined with their parent 
+% secondary level items iff the tertiary item is the only one having 
+% that particular parent item. This is achieved through the definition
+%\begin{verbatim}
+%\DeclareInstance{docindex}{changes}{std}{%
+%    file-extension = gls,
+%    item2 = fixed-r2a-nocomma,
+%    item3 = aloneaccept3,
+%    columns = 1,
+%    letter-format = {},
+%    letter-skip = 0pt
+% }
+%\end{verbatim}
+% where the difference to the default definition is in the values for 
+% the \textit{item3} and \textit{columns} keys.
+% 
+% For details on what they various keys mean, see the declaration of 
+% the \texttt{std} template of type \texttt{docindex} on 
+% page~\pageref{docindex:std}.
+% 
+% With the \package{docidx2e} package, configuration follows the same 
+% logic, even though it is much more technical as one has to define 
+% the instances without the help of a template. The default instance 
+% definitions for the \package{docidx2e} package are the
+% \begin{quote}
+%   |\@namedef{TP@I{}{docindex}{index}}#1#2{|\dots|}|\\
+%   |\@namedef{TP@I{}{docindex}{changes}}#1#2{|\dots|}|
+% \end{quote}
+% that begin on pages~\pageref{p:index-instance} 
+% and~\pageref{p:changes-instance} respectively.
+% 
+% 
+% 
+% 
+% 
+% \StopEventually{
+% %    \begin{thebibliography}{9}
+%    \bibitem{xindex}
+%      Achim Blumensath: \textit{The \package{xindex} package};
+%      \textsc{http:}/\slash 
+%      \texttt{www-mgi.\nolinebreak[3]informatik.\nolinebreak[3]^^A
+%      rwth-aachen.de}\slash \texttt{\textasciitilde blume}/.
+%    \bibitem{makeindex-paper}
+%      Pehong Chen, Michael A. Harrison:
+%      \textit{Index Preparation and Processing},
+%      Software: practice \& experience, vol. \textbf{19}, no. 9 (1988),
+%      897--915; 
+%      Computer Science Tech. Report 87/347, University of California,
+%      Berkeley, March 1987;
+%      \textsc{ctan:}\discretionary{}{}{\thinspace}\texttt{indexing}^^A
+%      \slash\texttt{makeindex}\slash\texttt{paper}\slash
+%      \texttt{ind.tex}.
+%    \bibitem{tclldoc}
+%      Lars Hellstr\"om: 
+%      \textit{The \package{tclldoc} package and class},
+%      v\,2.20 or newer;
+%      \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash 
+%      \texttt{latex}\slash \texttt{contrib}\slash 
+%      \texttt{tclldoc}\slash \texttt{tclldoc.dtx}. 
+%      Note: At the time of writing, this has not yet been uploaded 
+%      to CTAN.
+%    \bibitem{xdoc}
+%      Lars Hellstr\"om:
+%      \textit{The \package{xdoc} package --- experimental 
+%        reimplementations of features from \package{doc}, 
+%        second~prototype}, 2000--2003;
+%      \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash
+%      \texttt{latex}\slash \texttt{contrib}\slash \texttt{xdoc}\slash
+%      \texttt{xdoc2.dtx}.
+%    \bibitem{xindy}
+%      Roger Kehr: 
+%      \textit{\program{xindy} --- A Flexible Indexing System};
+%      \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{indexing}^^A
+%      \slash\texttt{xindy}/.
+%    \bibitem{LaTeX-project}
+%      The \LaTeX3 Project: \textit{The \LaTeX\ Project Home Page};
+%      \textsc{http:}/\slash\texttt{www.latex-project.org}/.
+%    \bibitem{multicol}
+%      Frank Mittelbach: \textit{An environment for multicolumn output};
+%      \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash
+%      \texttt{latex}\slash \texttt{required}\slash \texttt{tools}\slash
+%      \texttt{multicol.dtx}.
+%    \bibitem{doc}
+%      Frank Mittelbach, B.~Hamilton Kelly, Andrew Mills, Dave Love, and 
+%      Joachim \mbox{Schrod}: \textit{The \package{doc} and 
+%      \package{shortvrb} Packages}, The \LaTeX3 Project; ^^A , 1993~ff. 
+%      \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash 
+%      \texttt{latex}\slash \texttt{base}\slash \texttt{doc.dtx}.
+%    \end{thebibliography}
+% }
+% 
+% 
+% 
+% 
+% \section{Implementation}
+% 
+% \subsection{\package{docstrip} modules}
+% 
+% This file contains a number of \package{docstrip} module directives, 
+% and many of these guard code that is not going to be used. In part 
+% this mirrors the development of the code (and may get cleared up 
+% eventually), but most of this duplication has to do with making the 
+% code work in many different set-ups (some of which involve other 
+% packages whose interface is rapidly changing).
+% 
+% The modules which control \LaTeX\ code are:
+% \begin{description}
+%   \item[\textsf{pkg}]
+%     Main guard for code that is to end up in some \LaTeX\ package.
+%   \item[\textsf{template}]
+%     Guard for code which uses features of the \package{template} 
+%     package. This code will end up in the \package{docindex} package, 
+%     whereas the equivalent code which avoids using templates ends up 
+%     in the \package{docidx2e} package.
+%   \item[\textsf{default}]
+%     This code protects the default values for template keys. The 
+%     syntax for this is changing, so the default values are currently 
+%     being assigned in the template bodies instead.
+% \end{description}
+% 
+% The modules which control \program{makeindex} style files are:
+% \begin{description}
+%   \item[\textsf{ist}]
+%     Code for the main style file \texttt{docindex.ist}.
+%   \item[\textsf{idx}]
+%     Code for a style file which is like the main one, but the input 
+%     parameters are set to the same values as in the standard \LaTeX\ 
+%     \texttt{gind.ist}.
+%   \item[\textsf{glo}]
+%     Code for a style file which is like the main one, but the input 
+%     parameters are set to the same values as in the standard \LaTeX\ 
+%     \texttt{gglo.ist}.
+% \end{description}
+% 
+% 
+% \subsection{Initial stuff}
+% 
+%    \begin{macrocode}
+%<*pkg>
+\NeedsTeXFormat{LaTeX2e}
+\ProvidesPackage
+%<template>   {docindex}
+%<!template>   {docidx2e}
+   [2001/04/11 v1.00 doc index formatting package]
+%    \end{macrocode}
+%    
+% Since the \texttt{multicols} environment is used by the \texttt{std} 
+% template of type \texttt{docindex}, the \package{multicol} package 
+% must have been loaded.
+%    \begin{macrocode}
+\RequirePackage{multicol}
+%    \end{macrocode}
+% This will probably change in \package{docindex} once I get around to 
+% check how this kind of thing is implemented in the \LaTeXplus\ output 
+% routine.
+% 
+% Since the \texttt{docindex} pagestyle may be used the \package{xdoc} 
+% package must have been loaded. This also loads the \package{doc} 
+% package which contains the definition of |\pfill|.
+%    \begin{macrocode}
+\RequirePackage{xdoc2}[2001/03/26]
+%    \end{macrocode}
+% 
+% 
+% \begin{option}{oldkeywords}
+%   The \texttt{oldkeywords} option tells the \package{docindex} 
+%   package to not change the index entry keywords from the \package{doc} 
+%   defaults. The code for this option appears further down.
+%    \begin{macrocode}
+\DeclareOption{oldkeywords}{}
+%    \end{macrocode}
+% \end{option}
+% 
+% \begin{option}{usedocindexps}
+%   The \texttt{usedocindexps} option tells the \package{docindex} 
+%   package to set the pagestyle to \texttt{docindex} (defined by 
+%   \package{xdoc}) when typesetting the index. The code for this option 
+%   appears further down.
+%    \begin{macrocode}
+\DeclareOption{usedocindexps}{}
+%    \end{macrocode}
+% \end{option}
+% 
+%    \begin{macrocode}
+\ProcessOptions\relax
+%</pkg>
+%    \end{macrocode}
+% 
+% 
+% 
+% \subsection{Index style files}
+% \label{Ssec:ist}
+% 
+% The \program{makeindex} style files uses four commands. The most 
+% important command is \DescribeMacro{\indexitem}|\indexitem|, which 
+% has the two syntaxes
+% \begin{quote}
+%   |\indexitem|\marg{level}\marg{text}\marg{next level}\\
+%   |\indexitem|\marg{level}\marg{text}|{9}|\marg{numbers}^^A
+%     \marg{next level}  
+% \end{quote}
+% The \meta{level} is an integer in the range 1--3, the \meta{next level} 
+% is an integer in the range 0--3, the \meta{text} is the item text, 
+% and the \meta{numbers} is a list of (page or the like) numbers. The 
+% reason for this dual syntax is limitations of \program{makeindex}: 
+% there is no way of making the text inserted after an item depend on 
+% whether there are any page numbers for this item, so one cannot make 
+% \meta{numbers} a straightforward optional argument.
+% 
+% The level numbers specify at what level the item is. Level~1 
+% corresponds to |\item|, level~2 corresponds to |\subitem|, and 
+% level~3 corresponds to |\subsubitem|. The \meta{next level} number 
+% may also be 0, and that denotes non-|\indexitem| material such as a 
+% space between letter groups or the end of the index. The purpose of 
+% the \meta{next level} argument is to let the formatting of an item 
+% depend on what level the next item has, a feature that 
+% \program{makeindex} alone doesn't provide. Since \program{makeindex} 
+% only supports putting text in front of things, each new item must 
+% begin by inserting the closing brace on the second last argument and 
+% the very last argument of the \emph{previous} item before it can do 
+% anything for itself. This leads to the following contents of the 
+% \program{makeindex} |item_|\textellipsis\ parameters.
+% 
+% \xrefoff
+%    \begin{macrocode}
+%<*ist|idx|glo>
+item_0  "}{1}\n\\indexitem{1}{"
+item_1  "}{2}\n  \\indexitem{2}{"
+item_01 "}{2}\n  \\indexitem{2}{"
+item_x1 "}{2}\n  \\indexitem{2}{"
+item_2  "}{3}\n    \\indexitem{3}{"
+item_12 "}{3}\n    \\indexitem{3}{"
+item_x2 "}{3}\n    \\indexitem{3}{"
+%    \end{macrocode}
+% \SpecialIndex{\indexitem} ^^A I can't believe I'm using this!
+%    \begin{macrocode}
+delim_0 "}{9}{"
+delim_1 "}{9}{"
+delim_2 "}{9}{"
+delim_n ", "
+delim_r "--"
+%</ist|idx|glo>
+%    \end{macrocode}
+% \xrefon
+% 
+% 
+% \begin{macro}{\indexitem}
+% \begin{macro}{\DI@indexitem}
+% \begin{macro}{\DI@indexitem@}
+% \begin{macro}{\DI@last@level}
+%   The |\indexitem| command (and its subsidiary macros |\DI@indexitem| 
+%   and |\DI@indexitem@| only handle argument grabbing and some 
+%   elementary processing of level numbers. The formatting of the item 
+%   is instead handled by the |\DI@indexitem@|\meta{level}, where 
+%   \meta{level} is the roman numeral |i|, |ii|, or |iii|, family of 
+%   control sequences. |\indexitem| itself doesn't grab any arguments, 
+%   instead it inserts the contents of |\DI@last@level| as an 
+%   additional argument in front of |\DI@indexitem|. The actual 
+%   argument structures of the other macros are
+%   \begin{quote}
+%     |\DI@indexitem|\marg{last}\marg{this}\marg{text}^^A
+%       \marg{next/\texttt{9}}\\
+%     |\DI@indexitem@|\marg{cmd}\marg{last}|{9}|\marg{text}^^A
+%       |\NoValue|\marg{figures}\marg{next}
+%   \end{quote}
+%   where \meta{this} is the level of this item, \meta{next} is the 
+%   level of the next item, \meta{text} is the item text, and 
+%   \meta{figures} are the (page) numbers for this item. Several of the 
+%   arguments of |\DI@indexitem@| are immediately gobbled; they are 
+%   only used when the original |\indexitem| did not have a 
+%   \meta{numbers} argument.
+%   
+%   The |\DI@last@level| macro stores the level of the last item before 
+%   the current. It is set and used by |\DI@indexitem@|.
+%    \begin{macrocode}
+%<*pkg>
+\newcommand\indexitem{%
+   \relax
+   \expandafter\DI@indexitem \expandafter{\DI@last@level}%
+}%
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\DI@indexitem#1#2#3#4{%
+   \edef\DI@last@level{\number#2\expandafter}%
+   \ifnum #4=9
+      \expandafter\expandafter \expandafter\DI@indexitem@
+   \fi
+   \csname DI@indexitem@\romannumeral#2\expandafter\endcsname
+      {#1}{#4}{#3}\NoValue
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\DI@indexitem@#1#2#3#4#5#6#7{#1{#2}{#7}{#4}{#6}}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\DI@last@level{0}
+%</pkg>
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}\end{macro}
+% 
+% The \describecsfamily{DI@indexitem@\meta{level}}|\DI@indexitem@|^^A
+% \meta{level}, where \meta{level} is the lower case roman numeral form 
+% of the level number, family of control sequences have the syntax
+% \begin{quote}
+%   |\DI@indexitem@|\meta{level}\,\marg{previous}\marg{next}^^A
+%   \marg{text}\marg{figures}
+% \end{quote}
+% where \meta{previous} and \meta{next} are the levels of the previous 
+% and following index items, \meta{text} is the entry text of this 
+% item, and \meta{figures} are the (page) numbers for this item, if it 
+% has any, or the token |\NoValue|, if it hasn't.
+% 
+% 
+% \xrefoff
+%    \begin{macrocode}
+%<*ist|idx|glo>
+group_skip     "}{0}\n%^^A\n\\indexnewletter{0}{"
+heading_prefix ""
+heading_suffix ""
+headings_flag  1
+%</ist|idx|glo>
+%    \end{macrocode}
+% \SpecialIndex{\indexnewletter}
+% \xrefon
+% 
+% 
+% \begin{macro}{\indexnewletter}
+%   \changes{v\,1.00}{2001/04/05}{Made it \cs{outer}. (LH)}
+%   The |\indexnewletter| command is placed in front of a new letter 
+%   group. It has the syntax
+%   \begin{quote}
+%     |\indexnewletter|\marg{first}\marg{letter}\marg{next}
+%   \end{quote}
+%   where \meta{first} is a flag (|1| if this |\indexnewletter| 
+%   is at the very beginning of the index, |0| otherwise), \meta{letter} 
+%   is the letter name (according to the \program{makeindex} program; it 
+%   can be e.g.\ the string `Symbols') and \meta{next} is the level of 
+%   the next item (I think this will always be |1| with 
+%   \program{makeindex}). The command takes care of declining an offer 
+%   to join with the previous index item, inserts some vertical space 
+%   if the \meta{first} is |0|, print the \meta{letter} using 
+%   |\DI@letter@format|, and doesn't offer to join with the following 
+%   item.
+%    \begin{macrocode}
+%<*pkg>
+\@ifundefined{indexnewletter}{}{%
+   \PackageInfo
+%<template>      {docindex}
+%<!template>      {docidx2e}
+      {Command \protect\indexnewletter\space redefined}
+}
+\outer\def\indexnewletter#1#2#3{%
+   \DI@item@nojoin
+   \ifnum #1=\z@ \vspace{\DI@letter@skip}\fi
+   \DI@letter@format{#2}%
+   \def\DI@last@level{0}%
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+}
+%</pkg>
+%    \end{macrocode}
+% \end{macro}
+% 
+% The index style files also need to set some parameters which aren't 
+% directly connected to the commands provided by the \package{docindex} 
+% package. First there's the input style parameters:\xrefoff
+%    \begin{macrocode}
+%<*ist|idx|glo>
+actual '='
+quote '!'
+level '>'
+%    \end{macrocode}
+% Then the page precedence should be changed. This is mainly for the 
+% convenience of use with documents that |\DocInclude| files, since 
+% these by default number the files using letters.
+%    \begin{macrocode}
+page_precedence  "naArR"
+%    \end{macrocode}
+% In \texttt{docindex.ist}, both the \texttt{keyword} and the 
+% |page_compositor| strings are different from their standard values. It 
+% turns out to be hard to use a normal command as page compositor, 
+% because \program{makeindex} always rejects spaces and braces in the 
+% page number even if they is in the |page_compositor| parameter!
+%    \begin{macrocode}
+%<ist>keyword "\\xdocindexentry"
+%<ist>page_compositor "\\+"
+%    \end{macrocode}
+% \SpecialIndex{\+}
+% Finally, in the style file for the list of changes, the keyword must 
+% be changed to |\glossaryentry|.
+%    \begin{macrocode}
+%<glo>keyword "\\glossaryentry"
+%</ist|idx|glo>
+%    \end{macrocode}
+% \xrefon
+% 
+% 
+% \begin{option}{oldkeywords}
+% \begin{macro}{\XD@index@keyword}
+% \begin{macro}{\XD@glossary@keyword}
+% \begin{macro}{\XD@page@compositor}
+%   \changes{v\,1.00}{2001/04/05}{Changed it from \cs{PageCompositor-} to 
+%      \cs{+}. (LH)}
+%   To make the contents of the \texttt{.idx} and \texttt{.glo} files 
+%   compatible with the input parameter settings of 
+%   \texttt{docindex.ist}, some macros used by the \package{xdoc} 
+%   package must be redefined. This can however be stopped if the 
+%   \texttt{oldkeywords} option is passed to the \package{docindex} 
+%   package.
+%    \begin{macrocode}
+%<*pkg>
+\@ifpackagewith
+%<template>   {docindex}
+%<!template>   {docidx2e}
+   {oldkeywords}{}{
+   \edef\XD@index@keyword{\@backslashchar xdocindexentry}
+   \let\XD@glossary@keyword\XD@index@keyword
+   \def\XD@page@compositor{\@backslashchar +}
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}\end{option}
+% 
+% \changes{v\,1.00}{2001/03/25}{The index file is no longer a 
+%    \texttt{thedocindex} environment---the layout must instead be set 
+%    by the command which \cs{input}s the index. Introduced the 
+%    \cs{docindexguard} command to handle situations with incompatible 
+%    index styles. (LH)}
+% 
+% \begin{macro}{\docindexguard}
+% \begin{macro}{\DI@ind@setup}
+%   The first line of every \texttt{docindex} style sorted index file is
+%   \begin{quote}
+%     |\docindexguard{\endinput}|
+%   \end{quote}
+%   If the index file is inputted as a classical sorted index file then 
+%   this will produce an undefined command error and no more lines in 
+%   the index will be read. If the index file is inputted using the 
+%   conventions of the \package{docindex} package then the 
+%   |\docindexguard| will instead gobble the |\endinput| so that the 
+%   file will be read.
+%   
+%   One can also have the opposite problem: a classical style index file 
+%   is being input using \package{docindex} conventions. It is to 
+%   overcome this problem that the |\DI@ind@setup| command has been 
+%   introduced. Classical style index files begin by a |\begin| 
+%   command, so that command is temporarily redefined to print a warning 
+%   message and |\endinput| the file. Should the first command instead 
+%   be |\docindexguard| then everything will be reset to normal. To 
+%   accomplish this, |\DI@ind@setup| opens a group which should be 
+%   closed by the initial |\docindexguard| or |\begin|.
+%    \begin{macrocode}
+\def\DI@ind@setup{\bgroup
+   \def\docindexguard##1{\egroup}%
+   \def\begin##1{%
+      \egroup
+      \PackageWarningNoLine
+%<template>         {docindex}%
+%<!template>         {docidx2e}%
+         {Ignoring old style index file}
+      \endinput
+   }%
+}
+%</pkg>
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \xrefoff
+%    \begin{macrocode}
+%<*idx|glo|ist>
+preamble  "\\docindexguard{\\endinput}\n%^^A\n\\indexnewletter{1}{"
+postamble "}{0}\n\\endinput"
+%</idx|glo|ist>
+%    \end{macrocode}
+% \SpecialIndex{\docindexguard}
+% \SpecialIndex{\indexnewletter}
+% \xrefon
+% 
+% In summary, this is the BNF syntax for a sorted index file that is to 
+% be typeset using \package{docindex}:
+% \begin{syntax}
+%   \item[sorted index file]
+%     \meta{guard}\meta{lettergroups}|\endinput|
+%   \item[guard] |\docindexguard{\endinput}|
+%   \item[lettergroups] \meta{lettergroup}\branch 
+%     \meta{lettergroup}\meta{lettergroups}
+%   \item[lettergroup] \meta{heading}\meta{items}
+%   \item[heading] 
+%     |\indexnewletter|\marg{first}\marg{letter}\marg{next}
+%   \item[items] \meta{empty}\branch \meta{item}\meta{items}
+%   \item[item] |\indexitem|\marg{level}\marg{text}\marg{next}\branch
+%     |\indexitem|\marg{level}\marg{text}|{9}|\marg{numbers}\marg{next}
+% \end{syntax}
+% A \meta{level} is |1|, |2|, or |3|. A \meta{next} is |0|, |1|, |2|, or 
+% |3|. Within a \meta{lettergroup}, the \meta{next} of one \meta{item} 
+% or the \meta{heading} must equal the \meta{level} of the next 
+% \meta{item} and the \meta{next} of the last item must be |0|. The 
+% \meta{first} should be |1| in the first \meta{lettergroup} and |0| in 
+% all the others.
+% 
+% 
+% \subsection{Template mechanisms}
+% 
+% The \package{docindex} package loads the \package{xhj} and 
+% \package{galley2} packages to gain access to the \texttt{justification} 
+% type templates. This indirectly loads the \package{xparse} and 
+% \package{template} packages.
+%    \begin{macrocode}
+%<*pkg>
+%<template>\RequirePackage{xhj,galley2}
+%    \end{macrocode}
+% 
+% Since the \package{docidx2e} package doesn't use the template mechanisms 
+% provided by the \package{template} package, but still is to follow the 
+% logic of the \package{docindex} package which does use these 
+% mechanisms, it becomes convenient to define fakes for a couple of 
+% \package{template} commands. First \package{docidx2e} checks if the 
+% real \package{template} package has been loaded and emits a warning if 
+% it has.
+%    \begin{macrocode}
+%<*!template>
+\@ifpackageloaded{template}{
+   \PackageWarningNoLine{docidx2e}{The docidx2e package is only meant%
+      \MessageBreak for use when LaTeX2e* packages like 
+      template\MessageBreak are not available.}
+}{}
+%    \end{macrocode}
+% 
+% Before continuing with the definitions, some of the data structures 
+% used by the \package{template} mechanisms must be explained. A 
+% template \emph{instance} is really only a macro; what makes instances 
+% different from macros in general is that they usually aren't 
+% explicitly programmed. Instead they are formed by combining two 
+% different pieces of code: one which is the code part of some template, 
+% and one which is a piece of code which sets the \emph{container} 
+% macros\slash registers\slash parameters for the key values of this 
+% template. In general, the first piece of code contains the 
+% programming-like aspects of what the instance does, whereas the latter 
+% contains those that have to do with lauout and design. The advantage 
+% of this model is that it lets you implement many layouts without 
+% requiring you to know everything about \LaTeX\ programming that it 
+% would take to implement everything using macros.
+% 
+% Instances are stored in control sequences of the form
+% \begin{quote}
+%   \describecsfamily{TP@I{\meta{collection}}\break
+%      {\meta{type}}\break{\meta{name}}}
+%   |\TP@I|\marg{collection}\marg{type}\marg{name}
+% \end{quote}
+% The \meta{type} is the primary distinction between instances; for each 
+% type there exists a specification of what all instances of that type 
+% must do, and all instances of a type must be interchangeable. In 
+% particular, all instances of a given template type must have the same 
+% argument structure. The \meta{name} is simply the name used to 
+% identify the instance (amongst all other instances of that type). 
+% Finally, the \meta{collection} is something which can be used in 
+% circumstances where one needs to quickly switch between different 
+% definitions of an instance. If they have different \meta{collection}s 
+% then they can exist simutaneously; which of them is used is determined 
+% by which collection is currently active.
+% 
+% Collections are active on a ``per type'' basis; which collection is 
+% active for instances of type \meta{type} is determined by the 
+% contents of the \describecsfamily{TP@T{\meta{type}}} 
+% |\TP@T|\marg{type} control sequences, which are macros with the 
+% structure
+% \begin{quote}
+%   \marg{collection}\marg{arguments}
+% \end{quote}
+% If there is no instance with the requested name in the currently 
+% active collection then the instance with the same name from the 
+% normal collection (whose name is the empty string) will be used. The 
+% \meta{arguments} part of the macro is simply the number of arguments 
+% of instances of this type; it is only used when declaring templates.
+% 
+% \begin{macro}{\UseCollection}
+%   The |\UseCollection| command sets the active collection for a given 
+%   type. It has the syntax
+%   \begin{quote}
+%     |\UseCollection|\marg{type}\marg{collection}
+%   \end{quote}
+%   This macro was used up to v\,1.00 of \package{docindex} but a change 
+%   in the package logic made it unnecessary.
+%    \begin{macrocode}
+% \providecommand*\UseCollection[2]{%
+%    \expandafter\edef \csname TP@T{#1}\endcsname{%
+%       {#2}%
+%       {\expandafter\expandafter \expandafter\@secondoftwo
+%          \csname TP@T{#1}\endcsname}%
+%    }%
+% }
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\@letinstance}
+%   The |\@letinstance| macro |\let|s the (currently used) instance 
+%   with given name and type to the \meta{target} control sequence. It 
+%   has the syntax
+%   \begin{quote}
+%     |\@letinstance|\marg{target}\marg{type}\marg{name}
+%   \end{quote}
+%    \begin{macrocode}
+\def\@letinstance#1#2#3{%
+   \expandafter\let \expandafter#1%
+      \csname TP@I%
+         {\expandafter\expandafter \expandafter\@firstoftwo
+            \csname TP@T{#2}\endcsname}%
+         {#2}{#3}%
+      \endcsname
+   \ifx \relax#1%
+      \expandafter\let \expandafter#1\csname TP@I{}{#2}{#3}\endcsname
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\UseInstance}
+%   The |\UseInstance| calls the (currently used) instance with given 
+%   name and type. Its syntax is
+%   \begin{quote}
+%     |\UseInstance|\marg{type}\marg{name}\,\meta{arguments of instance}
+%   \end{quote}
+%    \begin{macrocode}
+\providecommand*\UseInstance[2]{%
+   \@letinstance\@tempa{#1}{#2}%
+   \ifx \relax\@tempa
+      \PackageError{docidx2e}{Instance #2 of type #1 undefined}\@eha
+   \else
+      \expandafter\@tempa
+   \fi
+}
+%</!template>
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% 
+% \subsection{Templates for index item formatting}
+% 
+% \begin{templatetype}{justification}
+%   In \package{docidx2e}, we have to provide a dummy definition of 
+%   |\TP@T{justification}|.
+%    \begin{macrocode}
+%<!template>\@namedef{TP@T{justification}}{{}{0}}
+%    \end{macrocode}
+% \end{templatetype}
+% 
+% \changes{v\,1.00}{2001/04/08}{Using \texttt{single} template rather 
+%    than the \texttt{std} template for the \texttt{indexitem}$n$ 
+%    instances of type \texttt{justification}. (LH)}
+% \begin{instance}{justification}{indexitem1}
+% \begin{instance}{justification}{indexitem2}
+% \begin{instance}{justification}{indexitem3}
+%   The \texttt{indexitem}\meta{level} instances of the 
+%   \texttt{justification} template set up paragraph indentation etc.\ 
+%   for a paragraph containing an index item at that level. The layout 
+%   is the same as that used by the \package{doc} package, but it is 
+%   not specified in quite the same way.
+%    \begin{macrocode}
+%<*template>
+\DeclareInstance{justification}{indexitem1}{single}{
+   leftskip=30pt, rightskip=15pt, startskip=-30pt, parfillskip=-15pt,
+   linefillskip=0pt plus 1fil, parindent=0pt
+}
+\DeclareInstance{justification}{indexitem2}{single}{
+   leftskip=30pt, rightskip=15pt, startskip=-15pt, parfillskip=-15pt,
+   linefillskip=0pt plus 1fil, parindent=0pt
+}
+\DeclareInstance{justification}{indexitem3}{single}{
+   leftskip=30pt, rightskip=15pt, startskip=-5pt, parfillskip=-15pt,
+   linefillskip=0pt plus 1fil, parindent=0pt
+}
+%</template>
+%<*!template>
+\@namedef{TP@I{}{justification}{indexitem1}}{%
+   \leftskip=30\p@
+   \rightskip=15\p@
+   \parindent=-30\p@
+   \parfillskip=-\rightskip
+}
+\@namedef{TP@I{}{justification}{indexitem2}}{%
+   \leftskip=30\p@
+   \rightskip=15\p@
+   \parindent=-15\p@
+   \parfillskip=-\rightskip
+}
+\@namedef{TP@I{}{justification}{indexitem3}}{%
+   \leftskip=30\p@
+   \rightskip=15\p@
+   \parindent=-5\p@
+   \parfillskip=-\rightskip
+}
+%</!template>
+%    \end{macrocode}
+% \end{instance}\end{instance}\end{instance}
+% 
+% 
+% 
+% \subsubsection{The \texttt{indexitem} template type}
+% 
+% \begin{templatetype}{indexitem}
+% \begin{macro}{\DI@item@nojoin}
+% \begin{macro}{\DI@item@join}
+%   The argument structure of a template of type \texttt{indexitem} is
+%   \begin{quote}
+%     \marg{previous}\marg{next}\marg{text}\marg{figures}
+%   \end{quote}
+%   \meta{previous} and \meta{next} are the level codes of the index 
+%   item before and after the current item, \meta{text} is the item text 
+%   of the current index item, and \meta{figures} are the  (page) numbers 
+%   for this item, if it has any, or the token |\NoValue|, if it hasn't.
+% 
+%   Templates of this type format and typeset one item in an index. In 
+%   doing so they may do pretty much anything as long as the other items 
+%   aren't affected: they may start and end paragraphs, change the 
+%   paragraph justification, \textellipsis
+%   
+%   There is however one area in which the rules are rather strict, and 
+%   that has to do with when two items can be joined. In a case where 
+%   item A is followed by item B, item A can propose to item B that they 
+%   should be joined and item B can then accept or decline this offer. 
+%   Technically the offer consists of defining the two macros 
+%   |\DI@item@join| and |\DI@item@nojoin|. If item B accepts the offer 
+%   it will execute |\DI@item@join| and if it declines the offer it 
+%   will execute |\DI@item@nojoin|. A typical definition of 
+%   |\DI@item@join| might be to insert a punctuation mark and a typical 
+%   definition of |\DI@item@nojoin| might be to end the current paragraph.
+%   
+%   There is however also a third case, namely that no offer was given. 
+%   In this case |\DI@item@nojoin| should be |\let| to |\@empty| and 
+%   |\DI@item@join| should be |\let| to |\@firstofone|. The reason for 
+%   this last rule is that |\DI@item@join| has the syntax
+%   \begin{quote}
+%     |\DI@item@join|\marg{no-join recovery code}
+%   \end{quote}
+%   where the \meta{no-join recovery code} is code that item B needs to 
+%   have executed if there is no join although item B would have 
+%   accepted it. |\DI@item@nojoin|, on the other hand, takes no 
+%   argument.
+%    \begin{macrocode}
+%<template>\DeclareTemplateType{indexitem}{4}
+%<!template>\@namedef{TP@T{indexitem}}{{}{4}}
+\let\DI@item@join=\@firstofone
+\let\DI@item@nojoin=\@empty
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{templatetype}
+% 
+% \begin{template}{indexitem}{fixed}
+%   The \texttt{fixed} template of type \texttt{indexitem} formats an 
+%   item as the items in \package{doc}'s \texttt{theindex} environment. 
+%   It is fixed in that it ignores the levels of the surrounding items.
+%   
+%   The keys for this template are:
+%   \begin{description}
+%     \keyvalitem{justification-setup}{i}
+%       This is a template instance of type \texttt{justification}. It 
+%       sets the justification for the paragraph containing the item, 
+%       unless the item is being joined with the preceeding item.
+%     \keyvalitem{pre-join}{b}
+%       A switch for whether the item should accept to be joined with 
+%       the item before. True means ``accept'', false means ``decline'' 
+%       (which is the default).
+%     \keyvalitem{nofig-action}{f1}
+%       If the \meta{figures} argument is |\NoValue| then the \meta{text} 
+%       argument is passed on to this macro for the actual formatting. 
+%       The default expansion is precisely the \meta{text}.
+%     \keyvalitem{fig-action}{f2}
+%       If the \meta{figures} argument is not |\NoValue| then the 
+%       \meta{text} and \meta{figures} arguments are passed on (in that 
+%       order) to this macro for the actual formatting. The default 
+%       expansion is
+%       \begin{quote}
+%         \meta{text}|\pfill|\meta{figures}
+%       \end{quote}
+%     \keyvalitem{post-join}{b}
+%       A switch for whether the item should offer to join with the 
+%       following item. True means ``make offer'', false (which is the 
+%       default) means ``don't make offer''. Making the offer is 
+%       furthermore conditioned by that the \meta{figures} argument is 
+%       |\NoValue|.
+%     \keyvalitem{nojoin-extra}{f0}
+%       Extra code which is inserted after the normal code for an item 
+%       if the item neither has any figures nor offers to join with the 
+%       following item. The default value is a space of length 
+%       \textit{linefillskip} followed by a |\nopagebreak|.^^A
+%       \changes{v\,0.03}{2001/02/24}{Added the \textit{nojoin-extra} 
+%          key. (LH)}^^A
+%       \changes{v\,0.03}{2001/02/25}{Added \cs{nopagebreak} from 
+%         \cs{efill} to default for \textit{nojoin-extra} key. (LH)}
+%     \keyvalitem{join-extra}{f0}
+%       Extra text which is inserted after the normal text of the item 
+%       if there is a join, by default a comma and a space.
+%     \keyvalitem{offjoin-extra}{f0}
+%       Extra code which is inserted after the normal text of the item 
+%       if a join is offered but declined. The default value is a space 
+%       of length \textit{linefillskip} followed by a |\nopagebreak| 
+%       (larger than the one from \textit{nojoin-extra}; if not for 
+%       this, the default could have been taken to be 
+%       |\DI@nojoin@extra|).
+%   \end{description}
+%   
+%   Note that the contents of the \textit{nojoin-extra}, 
+%   \textit{join-extra}, and \textit{offjoin-extra} keys must be robust 
+%   as they may be subjected to a |\protected@edef|.
+%   \changes{v\,0.03}{2001/02/24}{\cs{protected@edef}ing the macros
+%     \cs{DI@item@join} and \cs{DI@item@nojoin}. (LH)}
+%   
+%    \begin{macrocode}
+%<*template>
+\DeclareTemplate{indexitem}{fixed}{4}{
+   justification-setup =i{justification}      \DI@item@justification,
+   pre-join      =b  
+%<default>           {false}
+                                               DI@prejoin@,
+   nofig-action  =f1 
+%<default>           {#1}
+                                              \DI@nofig,
+   fig-action    =f2 
+%<default>           {#1\pfill#2}
+                                              \DI@hasfig,
+   post-join     =b  
+%<default>           {false}
+                                               DI@postjoin@,
+   nojoin-extra    =f0 
+%<default>           {\hspace*{\justification@g}
+%<default>            \protect\nopagebreak[2]}
+                                              \DI@nojoin@extra,
+   join-extra    =f0 
+%<default>           {,\space}
+                                              \DI@join@extra,
+   offjoin-extra =f0 
+%<default>           {\hspace*{\justification@g}
+%<default>            \protect\nopagebreak[4]}
+                                              \DI@offjoin@extra
+}{%
+%<*!default>
+   \let\ifDI@prejoin@\iffalse
+   \let\DI@nofig\@firstofone
+   \def\DI@hasfig##1##2{##1\pfill##2}%
+   \let\ifDI@postjoin@\iffalse
+   \def\DI@nojoin@extra{%
+      \hspace*{\justification@g}\protect\nopagebreak[2]%
+   }%
+   \def\DI@join@extra{,\space}%
+   \def\DI@offjoin@extra{%
+      \hspace*{\justification@g}\protect\nopagebreak[4]%
+   }%
+%</!default>
+   \DoParameterAssignments
+   \ifDI@prejoin@
+      \DI@item@join{\DI@item@justification}%
+   \else
+      \DI@item@nojoin\DI@item@justification
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \IfNoValueTF{#4}{%
+      \DI@nofig{#3}%
+      \ifDI@postjoin@
+         \protected@edef\DI@item@join##1{\DI@join@extra}%
+         \protected@edef\DI@item@nojoin{\DI@offjoin@extra\protect\par}%
+      \else
+         \DI@nojoin@extra\par
+      \fi
+   }{%
+      \DI@hasfig{#3}{#4}%
+      \par
+   }%
+   \ignorespaces
+}
+%    \end{macrocode}
+% \end{template}
+% 
+% \begin{instance}{indexitem}{fixed1}
+% \begin{instance}{indexitem}{fixed2}
+% \begin{instance}{indexitem}{fixed3}
+%   The \texttt{fixed1}, \texttt{fixed2}, and \texttt{fixed3} instances 
+%   of type \texttt{indexitem} are simply the \texttt{fixed} template 
+%   with different values assigned to the \textit{justification-setup} 
+%   key.
+%    \begin{macrocode}
+\DeclareInstance{indexitem}{fixed1}{fixed}
+   {justification-setup = indexitem1}
+\DeclareInstance{indexitem}{fixed2}{fixed}
+   {justification-setup = indexitem2}
+\DeclareInstance{indexitem}{fixed3}{fixed}
+   {justification-setup = indexitem3}
+%</template>
+%<*!template>
+\@namedef{TP@I{}{indexitem}{fixed1}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem1}%
+   \DI@item@nojoin
+   \DI@item@justification
+   \ifx \NoValue#4%
+      #3\nobreak\hfil\nopagebreak[2]%
+   \else
+      #3\pfill#4%
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \par
+}
+\@namedef{TP@I{}{indexitem}{fixed2}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem2}%
+   \DI@item@nojoin
+   \DI@item@justification
+   \ifx \NoValue#4%
+      #3\nobreak\hfil\nopagebreak[2]%
+   \else
+      #3\pfill#4%
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \par
+}
+\@namedef{TP@I{}{indexitem}{fixed3}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem3}%
+   \DI@item@nojoin
+   \DI@item@justification
+   \ifx \NoValue#4%
+      #3\nobreak\hfil\nopagebreak[2]%
+   \else
+      #3\pfill#4%
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \par
+}
+%</!template>
+%    \end{macrocode}
+% \end{instance}\end{instance}\end{instance}
+% 
+% \begin{instance}{indexitem}{fixed-r1a}
+% \begin{instance}{indexitem}{fixed-r2a-nocomma}
+% \begin{instance}{indexitem}{fixed-a3r}
+%   The \texttt{fixed-r1a}, \texttt{fixed-r2a-nocomma}, and 
+%   \texttt{fixed-a3r} instances of type \texttt{indexitem} are again 
+%   based on the \texttt{fixed} template, but here they always accept 
+%   (or offer) to join with one neighbouring item, whereas they always 
+%   reject to join with the other. As before, they differ in their 
+%   values of the \textit{justification-setup} key, and the 
+%   \texttt{-nocomma} is because that instance only inserts a space, 
+%   not a comma and a space, when items are joined.
+%    \begin{macrocode}
+%<*template>
+\DeclareInstance{indexitem}{fixed-r1a}{fixed}
+   {justification-setup = indexitem1, post-join = true}
+\DeclareInstance{indexitem}{fixed-r2a-nocomma}{fixed}
+   {justification-setup = indexitem2, 
+    post-join = true, join-extra = {\space}}
+\DeclareInstance{indexitem}{fixed-a3r}{fixed}
+   {justification-setup = indexitem3, pre-join = true}
+%</template>
+%<*!template>
+\@namedef{TP@I{}{indexitem}{fixed-r1a}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem1}%
+   \DI@item@nojoin
+   \DI@item@justification
+   \ifx \NoValue#4%
+      #3%
+      \def\DI@item@join##1{, }%
+      \def\DI@item@nojoin{\nobreak\hfil\nopagebreak[4]\par}%
+   \else
+      #3\pfill#4\par
+      \let\DI@item@join\@firstofone
+      \let\DI@item@nojoin\@empty
+   \fi
+   \ignorespaces
+}
+\@namedef{TP@I{}{indexitem}{fixed-r2a-nocomma}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem2}%
+   \DI@item@nojoin
+   \DI@item@justification
+   \ifx \NoValue#4%
+      #3%
+      \def\DI@item@join##1{ }%
+      \def\DI@item@nojoin{\nobreak\hfil\nopagebreak[4]\par}%
+   \else
+      #3\pfill#4\par
+      \let\DI@item@join\@firstofone
+      \let\DI@item@nojoin\@empty
+   \fi
+   \ignorespaces
+}
+\@namedef{TP@I{}{indexitem}{fixed-a3r}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem3}%
+   \DI@item@join{\DI@item@justification}%
+   \ifx \NoValue#4%
+      #3\hfil\nopagebreak[2]%
+   \else
+      #3\pfill#4%
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \par
+}
+%</!template>
+%    \end{macrocode}
+% \end{instance}\end{instance}\end{instance}
+% 
+% 
+% \begin{template}{indexitem}{aloneaccept}
+%   The \texttt{aloneaccept} template of type \texttt{indexitem} formats 
+%   an item as the items in \package{doc}'s \texttt{theindex} environment. 
+%   It accepts to be joined with the preceeding item if and only if 
+%   both that and the following item are at a lower level than the item 
+%   itself is.
+%   
+%   The keys for this template are:
+%   \begin{description}
+%     \keyvalitem{justification-setup}{i}
+%       This is a template instance of type \texttt{justification}. It 
+%       sets the justification for the paragraph containing the item, 
+%       unless the item is being joined with the preceeding item.
+%     \keyvalitem{ownlevel}{C}
+%       This is the (nominal) level of this item; it will accept a join 
+%       with the preceeding item if and only if the levels of both that 
+%       and the following item are different from this number. 
+%       \changes{v\,1.00}{2001/03/25}{Changed condition for accepting a 
+%         join from ``neighbouring item levels are lower'' to 
+%         ``neighbouring item levels are not equal to''. (LH)}
+%       The default is 2.
+%     \keyvalitem{nofig-action}{f1}
+%       If the \meta{figures} argument is |\NoValue| then the \meta{text} 
+%       argument is passed on to this macro for the actual formatting. 
+%       The default expansion is the \meta{text} followed by a space of 
+%       linefillskip.
+%     \keyvalitem{fig-action}{f2}
+%       If the \meta{figures} argument is not |\NoValue| then the 
+%       \meta{text} and \meta{figures} arguments are passed on (in that 
+%       order) to this macro for the actual formatting. The default 
+%       expansion is
+%       \begin{quote}
+%         \meta{text}|\pfill|\meta{figures}
+%       \end{quote}
+%     \keyvalitem{post-join}{b}
+%       A switch for whether the item should offer to join with the 
+%       following item. True means ``make offer'', false (which is the 
+%       default) means ``don't make offer''. Making the offer is 
+%       furthermore conditioned by that the \meta{figures} argument is 
+%       |\NoValue|.
+%     \keyvalitem{nojoin-extra}{f0}
+%       Extra code which is inserted after the normal code for an item 
+%       if the item neither has any figures nor offers to join with the 
+%       following item. The default value is a space of length 
+%       \textit{linefillskip}.
+%       \changes{v\,0.03}{2001/02/24}{Added the \textit{nojoin-extra} 
+%          key. (LH)}
+%     \keyvalitem{join-extra}{f0}
+%       Extra text which is inserted after the normal text of the item 
+%       if there is a join, by default a comma and a space.
+%     \keyvalitem{offjoin-extra}{f0}
+%       Extra code which is inserted after the normal text of the item 
+%       if a join is offered but declined, by default the 
+%       \textit{nojoin-extra} code followed by a |\nopagebreak|. 
+%   \end{description}
+%   
+%   Note that the contents of the \textit{nojoin-extra}, 
+%   \textit{join-extra}, and \textit{offjoin-extra} keys must be robust 
+%   as they may be subjected to a |\protected@edef|.
+%   \changes{v\,0.03}{2001/02/24}{\cs{protected@edef}ing the macros
+%     \cs{DI@item@join} and \cs{DI@item@nojoin}. (LH)}
+%   
+%    \begin{macrocode}
+%<*template>
+\DeclareTemplate{indexitem}{aloneaccept}{4}{
+   justification-setup =i{justification}      \DI@item@justification,
+   ownlevel      =C  
+%<default>           {2}
+                                              \DI@this@level,
+   nofig-action  =f1 
+%<default>           {#1}
+                                              \DI@nofig,
+   fig-action    =f2 
+%<default>           {#1\pfill#2}
+                                              \DI@hasfig,
+   post-join     =b  
+%<default>           {false}
+                                               DI@postjoin@,
+   nojoin-extra    =f0 
+%<default>           {\hspace*{\justification@g}}
+                                              \DI@nojoin@extra,
+   join-extra    =f0 
+%<default>           {,\space}
+                                              \DI@join@extra,
+   offjoin-extra =f0 
+%<default>           {\DI@nojoin@extra\protect\nopagebreak[4]}
+                                              \DI@offjoin@extra
+}{%
+%<*!default>
+   \def\DI@this@level{2}%
+   \let\DI@nofig\@firstofone
+   \def\DI@hasfig##1##2{##1\pfill##2}%
+   \let\ifDI@postjoin@\iffalse
+   \def\DI@nojoin@extra{\hspace*{\justification@g}}%
+   \def\DI@join@extra{,\space}%
+   \def\DI@offjoin@extra{\DI@nojoin@extra\protect\nopagebreak[4]}%
+%</!default>
+   \DoParameterAssignments
+   \ifnum \DI@this@level=#1
+      \DI@item@nojoin \DI@item@justification
+   \else\ifnum \DI@this@level=#2
+      \DI@item@nojoin \DI@item@justification
+   \else
+      \DI@item@join{\DI@item@justification}%
+   \fi\fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \IfNoValueTF{#4}{%
+      \DI@nofig{#3}%
+      \ifDI@postjoin@
+         \protected@edef\DI@item@join##1{\DI@join@extra}%
+         \protected@edef\DI@item@nojoin{\DI@offjoin@extra\protect\par}%
+      \else
+         \DI@nojoin@extra \par
+      \fi
+   }{%
+      \DI@hasfig{#3}{#4}%
+      \par
+   }%
+   \ignorespaces
+}
+%</template>
+%    \end{macrocode}
+% \end{template}
+% 
+% \begin{instance}{indexitem}{aloneaccept2}
+% \begin{instance}{indexitem}{aloneaceept3}
+%   The \texttt{aloneaccept2} and \texttt{aloneaccept3} instances of type 
+%   \texttt{indexitem} are simply the \texttt{aloneaccept} template 
+%   with the levels fixed to two and three, respectively.
+%    \begin{macrocode}
+%<*template>
+\DeclareInstance{indexitem}{aloneaccept2}{aloneaccept}
+   {justification-setup = indexitem2, ownlevel = 2}
+\DeclareInstance{indexitem}{aloneaccept3}{aloneaccept}
+   {justification-setup = indexitem3, ownlevel = 3}
+%</template>
+%<*!template>
+\@namedef{TP@I{}{indexitem}{aloneaccept2}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem2}%
+   \ifnum #1=\tw@
+      \DI@item@nojoin \DI@item@justification
+   \else\ifnum #2=\tw@
+      \DI@item@nojoin \DI@item@justification
+   \else
+      \DI@item@join{\DI@item@justification}%
+   \fi\fi
+   \ifx \NoValue#4%
+      #3\nobreak\hfil\vadjust{}%
+   \else
+      #3\pfill #4%
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \par
+}
+\@namedef{TP@I{}{indexitem}{aloneaccept3}}#1#2#3#4{%
+   \@letinstance\DI@item@justification{justification}{indexitem3}%
+   \ifnum #1=\thr@@
+      \DI@item@nojoin \DI@item@justification
+   \else\ifnum #2=\thr@@
+      \DI@item@nojoin \DI@item@justification
+   \else
+      \DI@item@join{\DI@item@justification}%
+   \fi\fi
+   \ifx \NoValue#4%
+      #3\nobreak\hfil\vadjust{}%
+   \else
+      #3\pfill #4%
+   \fi
+   \let\DI@item@join\@firstofone
+   \let\DI@item@nojoin\@empty
+   \par
+}
+%</!template>
+%    \end{macrocode}
+% \end{instance}\end{instance}
+% 
+% 
+% \subsubsection{The \texttt{docindex} template type}
+% 
+% \begin{templatetype}{docindex}
+%   A template of type \texttt{docindex} takes care of typesetting an 
+%   index found in a file (which is |\input|ted as part of this 
+%   process), hence using an instance of type \texttt{docindex} is 
+%   the same kind of action that the |\printindex| and |\printglossary| 
+%   commands make.
+%   
+%   The template decides from which file the index should be read. It 
+%   takes two arguments: the index prologue and the index epilogue. 
+%   These are two pieces of text (which may just as well include a 
+%   sectioning command) that are printed just before and after the 
+%   index. Either argument may be empty. Immediately after the file 
+%   containing the body of the index has been inputted, the template 
+%   must execute |\DI@item@nojoin| to make sure that the last item is 
+%   properly typeset.
+%   
+%   Templates of type \texttt{docindex} must begin by opening a group 
+%   and end by closing it. They must furthermore locally define the 
+%   following macros before any part of the index is typeset.
+%   \begin{description}
+%     \item[\cs{DI@indexitem@i}, \cs{DI@indexitem@ii}, and 
+%       \cs{DI@indexitem@iii}]
+%       Handlers for index items at level 1, 2, and 3 respectively. 
+%       These handlers must conform to the specification for 
+%       \texttt{indexitem} instances.
+%     \item[\cs{DI@letter@skip}, \cs{DI@letter@format}]
+%       These are described in the comments to the |\indexnewletter| 
+%       command.
+%     \item[\cs{+}]
+%       The command for typesetting the separator between two parts of 
+%       a composite (page) number. This is a parameterless macro.
+%   \end{description}
+%   
+%    \begin{macrocode}
+%<template>\DeclareTemplateType{docindex}{2}
+%<!template>\@namedef{TP@T{docindex}}{{}{2}}
+%    \end{macrocode}
+% \end{templatetype}
+% 
+% \begin{template}{docindex}{std}
+%   The \texttt{std} template of type \texttt{docindex} typesets an 
+%   index while providing all the formatting parameters of the 
+%   \package{doc} index and list of changes (and a few more).
+%   \changes{v\,1.00}{2001/04/08}{The \mbox{\textit{-font}} keyvals 
+%      renamed to \mbox{\textit{-setup}}, but the type stayed the 
+%      same (f0). (LH)}
+%   
+%   \label{docindex:std}
+%   The keys of the template are:
+%   \begin{description}
+%     \keyvalitem{file-name}{n}
+%       The base name of the file in which the index is stored, by 
+%       default the |\jobname|.\changes{v\,1.00}{2001/03/25}{Added 
+%       \textit{file-name} and \textit{file-extension} keys, removed 
+%       the \textit{default-prologue} and \textit{default-epilogue} 
+%       keys. (LH)}
+%     \keyvalitem{file-extension}{n}
+%       The extension of the file in which the index is stored, by 
+%       default \texttt{ind}.
+%     \keyvalitem{item1}{i}
+%       \texttt{indexitem} instance for level 1 items, by default 
+%       \texttt{fixed1}.
+%     \keyvalitem{item2}{i}
+%       \texttt{indexitem} instance for level 2 items, by default 
+%       \texttt{fixed2}.
+%     \keyvalitem{item3}{i}
+%       \texttt{indexitem} instance for level 3 items, by default 
+%       \texttt{fixed3}.
+%     \keyvalitem{columns}{C}
+%       The number of columns in the index, by default 3.
+%     \keyvalitem{reserved-height}{L}
+%       The minimal amount of vertical space that must be left on the 
+%       current page if the index is to start on it, by default 
+%       80\,pt.^^A
+%       \changes{v\,1.00}{2001/03/25}{Made \textit{reserved-height} work 
+%          even when \textit{columns} is 1 by using the 
+%          \package{multicol} macro \cs{enough@room}. (LH)}
+%     \keyvalitem{column-sep}{l}
+%       The horizontal separation between columns in the index, by 
+%       default 10\,pt. (This may seem strange in comparison with 
+%       \package{doc}, since |\IndexParms| contains the command 
+%       |\columnsep=15pt|, but \package{doc} doesn't execute 
+%       |\IndexParms| until \LaTeX\ is already in multi-column mode, and 
+%       then it is too late for the changed value to have any effect.)
+%     \keyvalitem{prologue-setup}{f0}
+%       Various commands setting layout parameters (e.g.\ the font) for 
+%       the prologue; by default empty.
+%     \keyvalitem{body-setup}{f0}
+%       Various commands setting layout parameters (e.g.\ the font) for 
+%       the body of the index; by default |\small|.
+%     \keyvalitem{epilogue-setup}{f0}
+%       Various commands setting layout parameters (e.g.\ the font) for 
+%       the epilogue; by default |\normalsize| (to counter the |\small| 
+%       in the \textit{body-setup}).
+%     \keyvalitem{letter-skip}{L}
+%       The skip inserted before a new letter group, by default 10\,pt 
+%       plus 2\,pt minus 3\,pt.
+%     \keyvalitem{letter-format}{f1}
+%       The macro which formats new letter groups; the argument is the 
+%       heading for the group, as generated by \program{makeindex}. By 
+%       defaults it typesets the argument in boldface, centered on a 
+%       line.
+%     \keyvalitem{pagestyle}{n}
+%       If this is nonempty then the pagestyle by that name will be 
+%       selected for the index. By default it is empty.
+%     \keyvalitem{parskip}{l}
+%       The value of |\parskip| to use inside the index, by default 
+%       0\,pt plus 1\,pt. This key value is likely to change as the 
+%       \LaTeXplus\ interfaces for galleys evolve.
+%       \changes{v\,0.03}{2001/02/27}{Added \textit{parskip} keyval. (LH)}
+%     \keyvalitem{page-compositor}{f0}
+%       The text that is typeset to separate two parts of a composite 
+%       (page) number, by default a hyphen.
+%       \changes{v\,1.00}{2001/04/05}{Added \textit{page-compositor} 
+%          keyval. (LH)}
+%   \end{description}
+%   
+%    \begin{macrocode}
+%<*template>
+\DeclareTemplate{docindex}{std}{2}{
+   file-name        =n
+%<default>         {\jobname}
+                                                    \DI@file@name,
+   file-extension   =n                   
+%<default>         {ind}
+                                                    \DI@file@ext,
+   item1            =i{indexitem} 
+%<default>         {fixed1}
+                                                    \DI@indexitem@i,
+   item2            =i{indexitem} 
+%<default>         {fixed2}
+                                                    \DI@indexitem@ii,
+   item3            =i{indexitem} 
+%<default>         {fixed3}
+                                                    \DI@indexitem@iii,
+   reserved-height  =L  
+%<default>         {80pt}
+                                                    \DI@reserved@height,
+   columns          =C  
+%<default>         {3}
+                                                    \DI@columns,
+   column-sep       =l  
+%<default>         {10pt}
+                                                    \columnsep,
+   prologue-setup    =f0 
+%<default>         {}
+                                                    \DI@prologue@setup,
+   body-setup        =f0 
+%<default>         {\small}
+                                                    \DI@body@setup,
+   epilogue-setup    =f0 
+%<default>         {\normalsize}
+                                                    \DI@epilogue@setup,
+   letter-skip      =L  
+%<default>         {10pt plus 2pt minus 3pt}
+                                                    \DI@letter@skip,
+   letter-format    =f1 
+%<default>         {\UseInstance{justification}{center}%
+%<default>          \textbf{#1}\nopagebreak\csname par\endcsname}
+                                                    \DI@letter@format,
+   pagestyle        =n  
+%<default>             {}
+                                                    \DI@pagestyle,
+   parskip          =l  
+%<default>             {0pt plus 1pt}
+                                                    \parskip,
+   page-compositor  =f0
+%<default>             {-}
+                                                    \+
+}{%
+   \begingroup
+%<*!default>
+   \def\DI@file@name{\jobname}%
+   \def\DI@file@ext{ind}%
+   \@letinstance\DI@indexitem@i{indexitem}{fixed1}%
+   \@letinstance\DI@indexitem@ii{indexitem}{fixed2}%
+   \@letinstance\DI@indexitem@iii{indexitem}{fixed3}%
+   \def\DI@reserved@height{80pt}%
+   \def\DI@columns{3}%
+   \columnsep=10pt%
+   \let\DI@prologue@setup\@empty
+   \def\DI@body@setup{\small}%
+   \def\DI@epilogue@setup{\normalsize}%
+   \def\DI@letter@skip{10pt plus 2pt minus 3pt}%
+   \def\DI@letter@format##1{%
+      \UseInstance{justification}{center}%
+      \textbf{##1}\nopagebreak\par
+   }%
+   \parskip=\z@\@plus\p@
+   \let\DI@pagestyle\@empty
+   \def\+{-}%
+%</!default>
+   \DoParameterAssignments
+   \IfFileExists{\DI@file@name.\DI@file@ext}{%
+      \ifnum \DI@columns>\@ne
+         \begin{multicols}{\DI@columns}%
+            [\DI@prologue@setup #1][\DI@reserved@height]%
+      \else
+         \enough@room{\DI@reserved@height}%
+         \DI@prologue@setup #1\par
+         \addvspace\multicolsep
+      \fi
+      \ifx \DI@pagestyle\@empty \else \pagestyle{\DI@pagestyle}\fi
+      \DI@body@setup
+      \DI@ind@setup
+      \input{\DI@file@name.\DI@file@ext}%
+      \DI@item@nojoin
+      \ifx \DI@pagestyle\@empty \else
+         \expandafter\thispagestyle \expandafter{\DI@pagestyle}%
+      \fi
+      \ifnum \DI@columns>\@ne
+         \end{multicols}%
+      \else
+         \enough@room\postmulticols
+         \addvspace\multicolsep
+      \fi
+      \DI@epilogue@setup #2\par
+   }{\typeout{No file \DI@file@name.\DI@file@ext.}}%
+   \endgroup
+}
+%    \end{macrocode}
+% \end{template}
+% 
+% 
+% \begin{instance}{docindex}{index}
+% \begin{option}{usedocindexps}
+%   The \texttt{index} instance of the \texttt{docindex} template type 
+%   prints the normal index (as opposed to the list of changes). There 
+%   are two different definitions of the instance: one which sets the 
+%   pagestyle in the index, and one which does not; which one is used 
+%   depends on whether the \texttt{usedocindexps} option has been 
+%   passed to the package or not.
+%    \begin{macrocode}
+\@ifpackagewith{docindex}{usedocindexps}{%
+   \DeclareInstance{docindex}{index}{std}{pagestyle=docindex}%
+}{%
+   \DeclareInstance{docindex}{index}{std}{}%
+}
+%</template>
+%    \end{macrocode}
+%   
+%   The implementations of the \texttt{index} instance in 
+%   \package{docidx2e} are slightly off in that they use \package{doc} 
+%   parameters for various settings in the extent such parameters exist.
+%   \changes{v\,0.03}{2001/02/24}{Added \cs{@nobreakfalse} in 
+%      \package{docidx2e} implementation; the first item in the index 
+%      does not directly follow a \cs{section}-type heading. (LH)}
+%   \label{p:index-instance}
+%    \begin{macrocode}
+%<*!template>
+\@ifpackagewith{docidx2e}{usedocindexps}{%
+   \@namedef{TP@I{}{docindex}{index}}#1#2{%
+      \begingroup
+      \@letinstance\DI@indexitem@i{indexitem}{fixed1}%
+      \@letinstance\DI@indexitem@ii{indexitem}{fixed2}%
+      \@letinstance\DI@indexitem@iii{indexitem}{fixed3}%
+      \columnsep=10pt%
+      \parskip=0pt plus 1pt%
+      \def\DI@letter@skip{10pt plus 2pt minus 3pt}%
+      \def\DI@letter@format##1{%
+         \par
+         \hb@xt@\hsize{\hfil\textbf{##1}\hfil}%
+         \nopagebreak
+      }%
+      \def\+{-}%
+      \IfFileExists{\jobname.ind}{%
+         \ifnum \c@IndexColumns>\@ne
+            \begin{multicols}{\c@IndexColumns}[#1][\IndexMin]%
+         \else
+            \enough@room{\IndexMin}%
+            #1\par
+            \addvspace\multicolsep
+         \fi
+         \pagestyle{docindex}%
+         \small
+         \@nobreakfalse
+         \DI@ind@setup
+         \input{\jobname.ind}%
+         \DI@item@nojoin
+         \thispagestyle{docindex}
+         \ifnum \c@IndexColumns>\@ne
+            \end{multicols}%
+         \else
+            \enough@room\postmulticols
+            \addvspace\multicolsep
+         \fi
+         \normalsize #2\par
+      }{\typeout{No file \jobname.ind.}}%
+      \endgroup
+   }
+}{%
+   \@namedef{TP@I{}{docindex}{index}}#1#2{%
+      \begingroup
+      \@letinstance\DI@indexitem@i{indexitem}{fixed1}%
+      \@letinstance\DI@indexitem@ii{indexitem}{fixed2}%
+      \@letinstance\DI@indexitem@iii{indexitem}{fixed3}%
+      \columnsep=10pt%
+      \parskip=0pt plus 1pt%
+      \def\DI@letter@skip{10pt plus 2pt minus 3pt}%
+      \def\DI@letter@format##1{%
+         \par
+         \hb@xt@\hsize{\hfil\textbf{##1}\hfil}%
+         \nopagebreak
+      }%
+      \def\+{-}%
+      \IfFileExists{\jobname.ind}{%
+         \ifnum \c@IndexColumns>\@ne
+            \begin{multicols}{\c@IndexColumns}[#1][\IndexMin]%
+         \else
+            \enough@room{\IndexMin}%
+            #1\par
+            \addvspace\multicolsep
+         \fi
+         \small
+         \@nobreakfalse
+         \DI@ind@setup
+         \input{\jobname.ind}%
+         \DI@item@nojoin
+         \ifnum \c@IndexColumns>\@ne
+            \end{multicols}%
+         \else
+            \enough@room\postmulticols
+            \addvspace\multicolsep
+         \fi
+         \normalsize #2\par
+      }{\typeout{No file \jobname.ind.}}%
+      \endgroup
+   }
+}
+%</!template>
+%    \end{macrocode}
+% \end{option}\end{instance}
+% 
+% 
+% \begin{instance}{docindex}{changes}
+%   The \texttt{changes} instance of the \texttt{docindex} template 
+%   type typesets a \package{doc} list of changes.
+%   \changes{v\,0.03}{2001/02/24}{Added \cs{@nobreakfalse} in 
+%      \package{docidx2e} implementation; the first item in the index 
+%      does not directly follow a \cs{section}-type heading. (LH)}
+%   \changes{v\,1.00}{2001/04/07}{Added \cs{makeatletter} in 
+%      \package{docidx2e} implementation; it doesn't hurt and it is 
+%      sometimes necessary (when commands that expand to private 
+%      control sequences are used in the argument of \cs{changes}). 
+%      (LH)}
+%    \begin{macrocode}
+%<*template>
+\DeclareInstance{docindex}{changes}{std}{
+   file-extension = gls,
+   item2 = fixed-r2a-nocomma,
+   item3 = fixed-a3r,
+   columns = 2, 
+   letter-format = {},
+   letter-skip = \z@skip
+}
+%</template>
+%    \end{macrocode}
+%   \label{p:changes-instance}
+%    \begin{macrocode}
+%<*!template>
+\@namedef{TP@I{}{docindex}{changes}}#1#2{%
+   \begingroup
+   \@letinstance\DI@indexitem@i{indexitem}{fixed1}%
+   \@letinstance\DI@indexitem@ii{indexitem}{fixed-r2a-nocomma}%
+   \@letinstance\DI@indexitem@iii{indexitem}{fixed-a3r}%
+   \columnsep=10pt%
+   \parskip=0pt plus 1pt%
+   \def\DI@letter@skip{\z@skip}%
+   \let\DI@letter@format\@gobble
+   \def\+{-}%
+   \IfFileExists{\jobname.gls}{%
+      \ifnum \c@GlossaryColumns>\@ne
+         \begin{multicols}{\c@GlossaryColumns}[#1][\GlossaryMin]%
+      \else
+         \enough@room{\GlossaryMin}%
+         #1\par
+         \addvspace\multicolsep
+      \fi
+      \small
+      \makeatletter
+      \@nobreakfalse
+      \DI@ind@setup
+      \input{\jobname.gls}%
+      \DI@item@nojoin
+      \ifnum \c@GlossaryColumns>\@ne
+         \end{multicols}%
+      \else
+         \enough@room\postmulticols
+         \addvspace\multicolsep
+      \fi
+      \normalsize #2\par
+   }{\typeout{No file \jobname.gls.}}
+   \endgroup
+}
+%</!template>
+%    \end{macrocode}
+% \end{instance}
+% 
+% \begin{macro}{\PrintIndex}
+% \begin{macro}{\PrintChanges}
+%   The |\PrintIndex| and |\PrintChanges| commands are redefined to use 
+%   the respective instances of template type \texttt{docindex}.
+%    \begin{macrocode}
+\renewcommand\PrintIndex{%
+   \UseInstance{docindex}{index}{\index@prologue}{}%
+   \global\let\PrintIndex\@empty
+}
+\renewcommand\PrintChanges{%
+   \UseInstance{docindex}{changes}{\glossary@prologue}{}%
+   \global\let\PrintChanges\@empty
+}
+%</pkg>
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% 
+% \section{Notes and acknowledgements}
+% 
+% The exact descriptions of the parameters of the \program{makeindex} 
+% program is the paper \cite{makeindex-paper} by Chen and Harrison, but 
+% I have seen claims that there are parameters not listed there 
+% (presumably becuase they were added after this paper was written). 
+% \texttt{docindex.ist} does not change any such undocumented 
+% parameter, however.
+% 
+% There are other index sorting programs than \package{makeindex} 
+% around, such as for example \program{x\r{\i}ndy}~\cite{xindy}. 
+% Should someone create index style files for such systems that are 
+% equivalent (or superior, for that matter) to \texttt{docindex.ist} 
+% then I would be happy to add them to the \package{docindex} 
+% distribution.
+% 
+% Most of the actual layout parameter settings used by the 
+% \package{docindex} package are not of my design, but copied from 
+% various other \LaTeX\ packages such as~\cite{multicol,doc} (mainly by 
+% Frank Mittelbach). I have however tried to sort out which parameters 
+% are actually in force under the various conditions---something which 
+% turned out to be less obvious than I originally suspected.
+% 
+% The idea to have the \texttt{docindex} type templates input the sorted 
+% index file (rather than simply setting up the formatting of it as was 
+% the case in v\,0.03) was taken from the \package{xindex} 
+% package~\cite{xindex} by Achim Blumensath.
+%
+% \hbadness=10000 
+%
+% \Finale
+% 
+%
+\endinput
\ No newline at end of file
diff --git a/Master/texmf-dist/source/latex/xdoc/docindex.ins b/Master/texmf-dist/source/latex/xdoc/docindex.ins
new file mode 100644
index 00000000000..d5d85cc6c32
--- /dev/null
+++ b/Master/texmf-dist/source/latex/xdoc/docindex.ins
@@ -0,0 +1,48 @@
+% This file is the docstrip installation script for the docindex package.
+% 
+% It may be distributed under the conditions of the LaTeX 
+% Project Public License, either version 1.2 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 1.2 or later is part of all distributions of LaTeX 
+% version 1999/12/01 or later.
+% 
+% Copyright 2001 Lars Hellstr\"om
+
+\input docstrip
+
+\keepsilent
+
+\preamble
+
+This file may be distributed and/or modified under the conditions 
+of the LaTeX Project Public License, either version 1.2 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 1.2 or later is part of all distributions of LaTeX 
+version 1999/12/01 or later.
+
+This file may only be distributed together with a copy of the source 
+file from which it was generated. You may distribute that source file 
+without this generated file.
+
+\endpreamble
+
+\declarepostamble\noendinput
+\endpostamble
+
+\generate{%
+   \usedir{tex/latex/misc}
+   \file{docindex.sty}{\from{docindex.dtx}{pkg,template}}%
+   \file{docidx2e.sty}{\from{docindex.dtx}{pkg}}%
+   \usepostamble\noendinput
+   \usedir{makeindex/latex}
+   \file{docindex.ist}{\from{docindex.dtx}{ist}}%
+%    \file{ngind.ist}{\from{docindex.dtx}{idx}}%
+%    \file{ngglo.ist}{\from{docindex.dtx}{glo}}%
+}
+
+\endbatchfile
+\end
diff --git a/Master/texmf-dist/source/latex/xdoc/xdoc2.dtx b/Master/texmf-dist/source/latex/xdoc/xdoc2.dtx
new file mode 100644
index 00000000000..c0d4a22d3d1
--- /dev/null
+++ b/Master/texmf-dist/source/latex/xdoc/xdoc2.dtx
@@ -0,0 +1,5166 @@
+% \CheckSum{2952}
+% 
+% \iffalse meta-comment
+% 
+% This file may be distributed and/or modified under the conditions 
+% of the LaTeX Project Public License, either version 1.2 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 1.2 or later is part of all distributions of LaTeX 
+% version 1999/12/01 or later.
+% 
+% Copyright 2000 2001 2002 Lars Hellstr\"om
+% 
+%<*driver>
+\documentclass{ltxdoc}
+\usepackage{array,longtable}
+
+\makeatletter
+\IfFileExists{xdoc2.sty}{%
+   \usepackage[dolayout]{xdoc2}
+   \NewMacroEnvironment{xrefcmd}{\XD@grab@harmless\relax}{1}%
+      {\MacroFont##1 \normalfont XXR-command}%
+      {\XDMainIndex{%
+         \levelsorted{##1 (XXR-command)}{\texttt{##1} (XXR-command)}%
+       }%
+       \XDMainIndex{%
+         \levelsame{XXR-commands:}\levelsorted{##1}{\texttt{##1}}%
+      }}%
+      {{##1}{XXR-command \texttt{##1}}}%
+      {}%
+   \@namedef{XD@harmless\string\Bslash}{%
+      \toks@=\expandafter{\the\expandafter\expandafter\expandafter\toks@
+         \csname XD@harmless@92\endcsname}%
+      \XD@harmless@
+   }%
+   \IfFileExists{docidx2e.sty}{%
+      \usepackage{docidx2e}%
+      \AtEndDocument{%
+         \typeout{*********************************}%
+         \typeout{* Use docindex.ist when sorting *}%
+         \typeout{* xdoc2.idx and xdoc2.glo. \@spaces\space*}%
+         \typeout{*********************************}%
+      }%
+   }%
+}{%
+   \newenvironment{option}[1]{\trivlist\item[]}{\endtrivlist}%
+   \newenvironment{xrefcmd}[1]{\trivlist\item[]}{\endtrivlist}%
+   \@ifpackagelater{doc}{2000/05/20}{}{%
+      \let\XD@fragile@meta=\meta
+      \def\meta{%
+         \ifx \protect\@typeset@protect
+            \expandafter\futurelet \expandafter\@let@token
+               \expandafter\XD@fragile@meta
+         \else
+            \noexpand\meta
+         \fi
+      }%
+   }%
+}
+\makeatother
+
+\providecommand\describecsfamily[1]{%
+   \leavevmode
+   \GenericDescribePrint{\MacroFont\Bslash#1}%
+   \ignorespaces
+}
+\providecommand\describeoption[1]{%
+   \leavevmode
+   \GenericDescribePrint{\MacroFont#1 \normalfont option}%
+   \ignorespaces
+}
+\providecommand\GenericDescribePrint[1]{%
+   \marginpar{\raggedleft\strut #1}%
+}
+\providecommand\Bslash{\bslash}
+\providecommand\DoNotIndexBy[1]{}
+\DoNotIndexBy{@}
+\DoNotIndexBy{@@}
+\DoNotIndexBy{XD@}
+
+\DeclareRobustCommand\package[1]{\textsf{#1}}
+\DeclareRobustCommand\LaTeXplus{\LaTeXe$*$}
+\newcommand\B{\penalty\exhyphenpenalty}
+\ProvideTextCommandDefault\textminus{\textendash}
+
+\hfuzz=15pt
+
+\AlsoImplementation
+\setcounter{IndexColumns}{2}
+
+\CodelineIndex
+\EnableCrossrefs
+\RecordChanges
+
+\begin{document}
+
+\DocInput{xdoc2.dtx}
+
+\PrintChanges
+\PrintIndex
+
+\end{document}
+%</driver>
+% \fi
+% 
+% \title{The \package{xdoc} package --- experimental reimplementations 
+%    of features from \package{doc}, second~prototype}
+% \author{Lars Hellstr\"om^^A
+%    \thanks{E-mail: \texttt{Lars.Hellstrom@math.umu.se}}}
+% \date{2003/07/07}
+% \maketitle
+% 
+% \DoNotIndex{\,,\-,\/,\ ,\#,\%,\&,\\,\^,\|}
+% \DoNotIndex{\@addtoreset,\@auxout,\@bsphack,\@cclv,\@ctrerr}
+% \DoNotIndex{\@eha,\@empty,\@esphack,\@evenfoot}
+% \DoNotIndex{\@firstofone,\@firstoftwo,\@for}
+% \DoNotIndex{\@gobble,\@gobblefour,\@gobbletwo}
+% \DoNotIndex{\@ifclassloaded,\@ifdefinable,\@ifpackagewith,\@ifundefined}
+% \DoNotIndex{\@input,\@latexerr,\@mainaux,\@mparswitchtrue}
+% \DoNotIndex{\@namedef,\@nameuse,\@ne,\@next,\@nil,\@oddfoot,\@partaux}
+% \DoNotIndex{\@partlist,\@secondoftwo,\@sptoken}
+% \DoNotIndex{\@tempswafalse,\@tempswatrue,\@totalleftmargin}
+% \DoNotIndex{\@typeset@protect,\@unexpandable@protect}
+% \DoNotIndex{\@vobeyspaces,\@writeckpt,\@xxxii}
+% \DoNotIndex{\active,\addto@hook,\addtolength,\advance,\AtBeginDocument}
+% \DoNotIndex{\baselineskip,\begingroup,\bgroup,\box,\boxmaxdepth}
+% \DoNotIndex{\catcode,\char,\clearpage,\closeout,\color@begingroup}
+% \DoNotIndex{\color@endgroup,\copy,\csname}
+% \DoNotIndex{\deadcycles,\DeclareOption,\DeclareRobustCommand,\def}
+% \DoNotIndex{\discretionary,\divide,\do@space,\dp}
+% \DoNotIndex{\edef,\egroup,\else,\em,\endcsname,\endgroup,\ensuremath}
+% \DoNotIndex{\escapechar,\everypar,\expandafter}
+% \DoNotIndex{\fi,\font,\footnotesize,\frenchspacing,\futurelet}
+% \DoNotIndex{\g@addto@macro,\gdef,\global}
+% \DoNotIndex{\hb@xt@,\hbox,\hfill,\hss,\ht,\hyphenchar}
+% \DoNotIndex{\if,\if@filesw,\if@inlabel,\if@mparswitch,\if@partsw}
+% \DoNotIndex{\if@reversemargin,\if@tempswa,\ifcase,\ifcat,\iffalse}
+% \DoNotIndex{\ifmmode,\ifnum,\ifodd,\iftrue,\ifx,\ignorespaces}
+% \DoNotIndex{\immediate,\include,\indexentry,\input,\inputlineno,\item}
+% \DoNotIndex{\itshape,\kern}
+% \DoNotIndex{\labelsep,\langle,\language,\leavevmode,\let,\long,\loop}
+% \DoNotIndex{\m@ne,\m@ta,\makelabel,\marginpar,\marginparsep,\maxdimen}
+% \DoNotIndex{\MessageBreak,\multiply}
+% \DoNotIndex{\NeedsTeXFormat,\newcommand,\newdimen,\newlanguage}
+% \DoNotIndex{\nfss@text,\noexpand,\normalfont,\normalmarginpar,\number}
+% \DoNotIndex{\obeyspaces,\openout,\or}
+% \DoNotIndex{\PackageError,\PackageInfo,\PackageWarning}
+% \DoNotIndex{\PackageWarningNoLine,\pagestyle,\paperwidth,\parbox,\part}
+% \DoNotIndex{\ProcessOptions,\protect,\protected@edef,\protected@write}
+% \DoNotIndex{\protected@xdef,\ProvidesPackage}
+% \DoNotIndex{\raggedleft,\raggedright,\rangle,\relax,\renewcommand}
+% \DoNotIndex{\repeat,\RequirePackage}
+% \DoNotIndex{\setbox,\setlength,\sixt@@n,\space,\string,\strut,\strutbox}
+% \DoNotIndex{\textasciicircum,\textasciitilde,\textbackslash,\textbar}
+% \DoNotIndex{\textbf,\textbraceleft,\textbraceright,\textdollar}
+% \DoNotIndex{\textgreater,\textless,\textquotedbl,\textquoteleft}
+% \DoNotIndex{\textquoteright,\texttt,\textunderscore,\textvisiblespace}
+% \DoNotIndex{\textwidth,\the,\topsep,\trivlist,\tw@}
+% \DoNotIndex{\uccode,\unhbox,\unrestored@protected@xdef,\unvbox}
+% \DoNotIndex{\uppercase}
+% \DoNotIndex{\vbox,\vss,\vtop,\write,\xdef,\z@}
+% 
+% \changes{prot1}{2000/06/15}{Started writing first prototype. (LH)}
+% \changes{prot2}{2000/07/13}{Began work on the second prototype. (LH)}
+% 
+% \begin{abstract}
+%   The \package{xdoc} package contains reimplementations of some of 
+%   the features found in the standard \LaTeX\ \package{doc} 
+%   package~\cite{doc} by Mittelbach \emph{et~al. }The ultimate goals 
+%   for these reimplementations are that the commands should be better, 
+%   easily configurable, and be easy to extend, but this is only a 
+%   second prototype implementation and nothing in it is guaranteed to 
+%   be the same in the third prototype.\footnote{But there are no 
+%   guarantees there will ever be a third prototype either.}
+% \end{abstract}
+% 
+% \tableofcontents
+% 
+% 
+% \section{Usage}
+% 
+% When I began working on this package I thought that there would be no 
+% need for a usage section (at least on the prototype stage)---either you 
+% are interested in using the new features and then you might just as 
+% well read the descriptions of the commands in the implementation part 
+% of this document (they are written as specifications of what the 
+% commands do), or else you can simply insert a |\usepackage|\B|{xdoc2}| 
+% in the preamble and see how things work a little better than when you 
+% simply use \package{doc}---but with some features it became natural 
+% to introduce incompatible changes and some new features ought to be 
+% mentioned. Hence I wrote a short section on usage after all.
+% 
+% It is my intention that this document will eventually evolve into the 
+% source for a package \package{xdoc}\footnote{The name \package{doc2} 
+% has also been discussed; we'll see when we get there.} which will 
+% either build on the \package{doc} package and provide better 
+% implementations of many of its features, or replace it completely, 
+% but this document is still only the source for a prototype for that 
+% package. As I believe that the need for some improvement in this area 
+% is rather large however, I have decided to release this prototype so 
+% that other people can use it in their documents or create packages that 
+% are based on it. In doing so, one must of course bear in mind that this 
+% prototype needs not be compatible with the final \package{xdoc} 
+% package, and to overcome most incompatibility problems I therefore 
+% release it under the variant name \package{xdoc2}. This way, documents 
+% based on this prototype can still be typeset using the package they 
+% were written for long after the next \package{xdoc} prototype (or final 
+% version) is released.
+% 
+% Thus although this document frequently speaks of \package{xdoc}, you 
+% might just as well read it as \package{xdoc2}.
+% 
+% 
+% \subsection{Changes to old features}
+% 
+% Whereas \package{doc} more or less assumes that all pages have the 
+% same layout, \package{xdoc} takes measures to ensure that the 
+% \package{doc} features support two-sided document designs. If the 
+% left margin has been widened to better accommodate long macro names 
+% however (like for example the \package{ltxdoc} document class does), 
+% then you may find that the outer margin on right (odd) pages is too 
+% narrow for printing macro names in. The remedy for this is the
+% \GenericDescribePrint{\MacroFont dolayout \normalfont option}^^A
+% \SortIndex{dolayout}{\texttt{dolayout} option\encapchar 
+% usage}\texttt{dolayout} option; in two-sided mode it causes 
+% \package{xdoc} to recompute the |\oddsidemargin| so that the outer 
+% margin has the same size on right pages as it previously did on left 
+% pages. In documents which are not processed in two-sided mode the 
+% \texttt{dolayout} option has no effect.
+% 
+% |\DocInput| has been changed to not make percent a comment character 
+% upon return unless it was before the |\DocInput|. This makes |\DocInput| 
+% nestable and I recommend that \texttt{.dtx} files which input other 
+% \texttt{.dtx} files use |\DocInput| for this.
+% 
+% The |\DocInclude| command, which is defined by the \package{ltxdoc} 
+% document class rather than \package{doc}, is also by default 
+% redefined in an incompatible manner by \package{xdoc}, but you can 
+% stop \package{xdoc} from making incompatible changes if you pass it the 
+% option \GenericDescribePrint{\MacroFont olddocinclude \normalfont
+% option}\SortIndex{olddocinclude}{\texttt{olddocinclude} option^^A
+% \encapchar usage}\texttt{olddocinclude}. The main incompatibility 
+% lies in that the default redefinition of |\DocInclude| behaves purely 
+% as an |\include| command which |\DocInput|s a \texttt{.dtx} file rather 
+% than merely |\input|ting a \texttt{.tex} file---you must pass the 
+% \GenericDescribePrint{\MacroFont fileispart \normalfont option}^^A
+% \SortIndex{fileispart}{\texttt{fileispart} option\encapchar 
+% usage}\texttt{fileispart} option to \package{xdoc} to get the |\part| 
+% headings etc.\ for each new file---but there are also minor changes 
+% in the appearance of these headings, in how page styles are set, and 
+% in how the information presented in the page footer is obtained.
+% 
+% Other changes are as far as I can tell minor and within the bounds of 
+% expected behaviour, but code that relies on the implementation of some 
+% feature in \package{doc} may of course behave differently or break 
+% completely. Note in particular that the formats of the internal 
+% \package{doc} variables |\saved@macroname|, |\macro@namepart|, and 
+% |\index@excludelist| have changed completely (see 
+% Section~\ref{Sec:Changes}, Subsection~\ref{Ssec:Scanning macrocode}, 
+% and Subsection~\ref{Ssec:Index-exclude} respectively)---hence any hack 
+% involving one of these must be revised before it is used with 
+% \package{xdoc}. These are however exceptions; in my experience the most 
+% noticeable changes not listed above are that the index exclude 
+% mechanism actually works for control sequences whose names consist of 
+% a single non-letter and that symbols get sorted in a different order.
+% 
+% 
+% \subsection{Some notable new features}
+% 
+% The main new feature is the \DescribeMacro\NewMacroEnvironment
+% |\NewMacroEnvironment| command, which defines a new \texttt{macro}-like 
+% environment. The command offers complete control of the argument 
+% structure, the formatting of the marginal heading, the code for making 
+% index entries, and the change entry sorting and formatting, but the 
+% syntax is too complex to explain here. Those who are interested in 
+% using it should read Section~\ref{Sec:Macro-environments}. In 
+% particular, Subsections~\ref{Ssec:Macro&environment}--^^A
+% \ref{Ssec:More macros} contain several examples of how it can be 
+% used. In addition to using |\New|\-|Macro|\-|Environment| for 
+% redefining the \DescribeEnv{macro}\texttt{macro} and 
+% \DescribeEnv{environment}\texttt{environment} environments, 
+% \package{xdoc} also defines an \DescribeEnv{option}\texttt{option} 
+% environment (which is intended for document class and package 
+% options) and a \DescribeEnv{switch}\texttt{switch} environment (which 
+% is intended for switches defined using |\newif|; the argument should 
+% not include the |\if|).
+% 
+% There is also a companion command \DescribeMacro\NewDescribeCommand
+% |\NewDescribeCommand| which defines new commands similar to 
+% |\Describe|\-|Macro| and |\Describe|\-|Env|. The syntax of 
+% |\New|\-|Describe|\-|Command| is also too complex to explain here, so 
+% I have to refer readers who want to use it to Section~^^A
+% \ref{Sec:Describing}. Two more commands which are defined in that 
+% section are \DescribeMacro\describeoption|\describe|\-|option|, which 
+% is the \texttt{describe}\dots\ companion of the \texttt{option} 
+% environment, and \DescribeMacro\describecsfamily
+% |\describe|\-|cs|\-|family| which is meant for describing control 
+% sequence families (see the table on page~\pageref{Tab:CS-families} for 
+% examples of what I mean). The argument of this latter command is simply 
+% the material you would put between |\csname| and |\endcsname|. Variant 
+% parts are written as |\meta|\B\marg{text} and print as one would expect 
+% them to (but notice that the \meta{text} is a moving argument) whereas 
+% most other characters can be written verbatim without any special 
+% quoting (but |\|, |{|, |}|, and |%| need quoting; see the comments to 
+% the definition of |\describe|\-|cs|\-|family| for information on how 
+% to do that).
+% 
+% The \DescribeMacro\DoNotIndexBy|\DoNotIndexBy| command tells the 
+% commands that make index entries for macros to ignore a certain 
+% character sequence when the index entries are sorted. The 
+% |\DoNotIndexBy| command takes one argument: the character sequence to 
+% ignore. If |\DoNotIndexBy| is used more than once then the indexing 
+% commands will look for, and if it finds it ignore, each of the 
+% character sequences given to it, starting with the one specified last.
+% 
+% It has already been mentioned that the |\DocInclude| command has been 
+% changed. What has not been mentioned is its companion 
+% \DescribeMacro\setfileinfo|\setfileinfo|, 
+% which the partfiles should use for setting the date and version 
+% information presented in the page footer, but that is explained in 
+% detail in Subsection~\ref{Ssec:New DocInclude}.
+% 
+% Finally there is a new variant of the |\changes| command which is 
+% intended for changes that, although not limited to a single macro and 
+% thus being ``general'' changes in the \package{doc} terminology, affect 
+% only a few (probably widely dispersed) macros (or whatever). The basic 
+% idea is that you can define a change with a specific version, date, 
+% and text using the \DescribeMacro{\definechange}|\definechange| command 
+% and then recall those parameters later using the 
+% \DescribeMacro{\usechange}|\usechange| command. Primarily this ensures 
+% that the entry texts are identical so that \package{makeindex} will 
+% combine them into one entry, but it is also specified which macro 
+% was changed at which page. See Section~\ref{Sec:Changes} for more 
+% details. Another new feature concerning |\changes| is that there is 
+% now support for sorting version numbers according to mathematical 
+% order rather than ASCII order. Traditionally the version numbers 
+% \texttt{2}, \texttt{11}, and \texttt{100} would have been sorted so 
+% that \texttt{100}${}<{}$\texttt{11}${}<{}$\texttt{2}, but if they are 
+% entered as \DescribeMacro{\uintver}|\uintver{2}|, |\uintver{11}|, and 
+% |\uintver{100}| then they will be sorted as 
+% \texttt{2}${}<{}$\texttt{11}${}<{}$\texttt{100}. The argument of 
+% |\uintver| must be a \TeX\ \meta{number}.
+% 
+% \medskip
+% 
+% \package{xdoc} also contains several features which are of little use 
+% as direct user commands, but which can simplify the definitions of other 
+% commands. The foremost of these are the `harmless character strings', 
+% which can be seen as a datatype for (short pieces of) verbatim text. 
+% \TeX\ typesets a harmless character string in pretty much the same way 
+% as the corresponding string of `other' tokens, but the harmless 
+% character string can also be written to file and read back arbitrarily 
+% many times without getting garbled, it doesn't make \package{makeindex} 
+% choke, and it survives being fed to a |\protected@edef|. The most 
+% important commands related to harmless character strings are 
+% \DescribeMacro\PrintChar|\PrintChar|, which is used for representing 
+% problematic characters, and \DescribeMacro\MakeHarmless|\MakeHarmless|, 
+% which converts arbitrary \TeX\ code to the corresponding harmless 
+% character string.
+% 
+% The superfluity of indexing commands in \package{doc} has been 
+% replaced by the single command \DescribeMacro\IndexEntry|\IndexEntry|, 
+% which has been designed with the intention that it should provide a 
+% clear interface between the user level macros and the index sorting 
+% program. It takes three arguments: the index entry specification, the 
+% name of the encapsulation scheme that should be used, and the number to 
+% put in the index. The index entry specification is a sequence of 
+% |\LevelSame| and\slash or |\LevelSorted| commands, which have the 
+% respective syntaxes
+% \begin{quote}
+%   \DescribeMacro\LevelSame|\LevelSame|\marg{text}\\
+%   \DescribeMacro\LevelSorted|\LevelSorted|\marg{sort key}\marg{text}
+% \end{quote}
+% Each such command specifies one level of the index entry. In the case of 
+% |\LevelSorted|, the \meta{text} is what will be written in the sorted 
+% index at that level and \meta{sort key} is what the index-sorting 
+% program should look at when sorting the entry (at that level). In the 
+% case of |\LevelSame|, the \meta{text} is used both as sort key and 
+% contents of entry in the sorted index. The first command is for the 
+% topmost level and each subsequent command is for the next sublevel. 
+% The complete description appears in Subsection~\ref{Ssec:IndexEntry}.
+% 
+% \package{xdoc} also contains support for external cross-referencing 
+% programs (see Subsection~\ref{Ssec:XXR} for details) and a system for 
+% determining whether a piece of text falls on an even or an odd page 
+% (see Section~\ref{Sec:Twoside} for details). I expect that the latter 
+% system will eventually migrate out of \package{xdoc}, either to a 
+% package of its own, or into oblivion because the \LaTeXplus\ output 
+% routine makes it obsolete.
+% 
+% 
+% \subsection{The \package{docindex} package}
+% 
+% As of prototype version 2.2, the \package{xdoc} package has a companion 
+% package \package{docindex}~\cite{docindex} which provides improved 
+% formatting of the index and list of changes. \package{xdoc} works fine 
+% without \package{docindex}, however.
+% 
+% 
+% \subsection{A note on command names}
+% 
+% The \package{doc} package defines several commands with mixed-case 
+% names which (IMHO) should really have all-lower-case names (according 
+% to the rule of thumb spelled out in \cite[Ssec.~2.4]{clsguide}) since 
+% people use them in the capacity of being the author of a \texttt{.dtx} 
+% file rather than in the capacity of being the writer of a class or 
+% package. The names in question are
+% \begin{longtable}{ll}
+%   \textbf{Name in \package{doc}}& \textbf{Better (?) name}\endhead
+%   \cs{AlsoImplementation}& \cs{alsoimplementation}\\
+%   \cs{CharacterTable}& \cs{charactertable}\\
+%   \cs{CharTableChanges}& \cs{chartablechanges}\\
+%   \cs{CheckModules}& \cs{checkmodules}\\
+%   \cs{CheckSum}& \cs{checksum}\\
+%   \cs{CodelineIndex}& \cs{codelineindex}\\
+%   \texttt{CodelineNo} (counter)& \texttt{codelineno}\\
+%   \cs{CodelineNumbered}& \cs{codelinenumbered}\\
+%   \cs{DeleteShortVerb}& \cs{deleteshortverb}\\
+%   \cs{DescribeEnv}& \cs{describeenv}\\
+%   \cs{DescribeMacro}& \cs{describemacro}\\
+%   \cs{DisableCrossrefs}& \cs{disablecrossrefs}\\
+%   \cs{DocInput}& \cs{docinput}\\
+%   \cs{DoNotIndex}& \cs{donotindex}\\
+%   \cs{DontCheckModules}& \cs{dontcheckmodules}\\
+%   \cs{EnableCrossrefs}& \cs{enablecrossrefs}\\
+%   \cs{Finale}& \cs{finale}\\
+%   \texttt{GlossaryColumns} (counter)& \texttt{glossarycolumns}\\
+%   \cs{GlossaryPrologue}& \cs{glossaryprologue}\\
+%   \texttt{IndexColumns} (counter)& \texttt{indexcolumns}\\
+%   \cs{IndexInput}& \cs{indexinput}\\
+%   \cs{IndexPrologue}& \cs{indexprologue}\\
+%   \cs{MakePrivateLetters}& \cs{makeprivateletters}\\
+%   \cs{MakeShortVerb}& \cs{makeshortverb}\\
+%   \cs{OnlyDescription}& \cs{onlydescription}\\
+%   \cs{PageIndex}& \cs{pageindex}\\
+%   \cs{PrintChanges}& \cs{printchanges}\\
+%   \cs{PrintIndex}& \cs{printindex}\\
+%   \cs{RecordChanges}& \cs{recordchanges}\\
+%   \cs{SortIndex}& \cs{sortindex}\\
+%   \cs{SpecialEscapechar}& \cs{specialescapechar}\\
+%   \texttt{StandardModuleDepth} (counter)& \texttt{standardmoduledepth}\\
+%   \cs{StopEventually}& \cs{stopeventually}
+% \end{longtable}
+% \noindent With the exception for \texttt{CodelineNo},\footnote{Where I 
+% recommend using \texttt{codelineno} instead of \texttt{CodelineNo}, 
+% \cs{PrintCodelineNo} instead of \cs{theCodelineNo}, and 
+% \cs{thecodelineno} instead of \cs{number}\cs{c@CodelineNo}; see 
+% Subsection~\ref{Ssec:CodelineNo}.} I haven't changed any of the 
+% \package{doc} names in this \package{xdoc} prototype, nor introduced any 
+% of the ``better names'' as alternatives, but I think the matter should 
+% be given a bit of thought during the future development of 
+% \package{doc}\slash \package{xdoc}. 
+% 
+% For completeness, I should also remark that there are several macros 
+% that \package{doc} gives mixed-case names which I haven't listed above. 
+% The logo command names have special capitalizing rules by tradition. 
+% Some macros and named registers---for example |\Docstyle|\-|Parms|, 
+% |\Index|\-|Parms|, |\Macro|\-|Font|, |\Macro|\-|Topsep|, 
+% |\Make|\-|Percent|\-|Ignore|, and |\Print|\-|Macro|\-|Name|---are part 
+% of the package or document class writer's interface to \package{doc}, 
+% although I cannot claim it to be obvious that for example 
+% |\Index|\-|Parms| and the \texttt{IndexColumns} counter should belong 
+% to different classes here (but several of these control sequences will 
+% probably disappear from the interface in \LaTeXplus\ anyway, so the 
+% problem isn't that important). The |\Special|\dots\B|Index| commands 
+% (and their even more special variants, such as 
+% |\Left|\-|Brace|\-|Index|) are internal commands rather than user level 
+% commands. Finally there is the |\Get|\-|File|\-|Info| command, which I 
+% doubt there is any point in having.
+% 
+% 
+% \StopEventually{}
+% 
+% 
+% \subsection{\package{docstrip} modules}
+% 
+% The \package{docstrip} modules in \texttt{xdoc2.dtx} are:
+% \begin{description}
+%   \item[\textsf{pkg}]
+%     This module directive surrounds the code for the \package{xdoc} 
+%     package.
+%   \item[\textsf{driver}]
+%     The driver.
+%   \item[\textsf{internals}]
+%     This module contains an alternative replacement text for the 
+%     |\Print|\-|Visible|\-|Char| command that uses ``\LaTeX\ internal 
+%     character representation'' (i.e., as much as possible 
+%     encoding-specific commands---|\text|\textellipsis\ commands and 
+%     the like) rather than the primitive |\char| command for 
+%     typesetting visible characters. 
+%     It is provided as a separate module mainly for compability with 
+%     prototype version~2.0, as this alternative definition can (as of 
+%     prot.\,2.1) be chosen by passing the option 
+%     \describeoption{notrawchar}\texttt{notrawchar} to \package{xdoc}.
+%   \item[\textsf{economical}]
+%     There is little point in storing the harmless representations of 
+%     the 161 non-visible-ASCII characters as these representations are 
+%     always the same and can be formed on the fly whenever they are 
+%     needed. The \textsf{economical} modules contain some alternative 
+%     code which makes use of this fact to reduce the number of control 
+%     sequences used for storing the table of harmless representations. 
+%     The \Module{economical} module appears inside the \Module{pkg} 
+%     module.
+%   \item[\textsf{xdoc2}]
+%     This module contains code for compability with previous releases 
+%     of \package{xdoc2}. It will not be included in \package{xdoc3} 
+%     or \package{xdoc} (whichever is the next major version).
+%   \item[\textsf{enccmds}]
+%     This module contains the code for defining two \texttt{macro}-like 
+%     environments for encoding-specific commands. These are not included 
+%     in the \package{xdoc} package since so few \texttt{.dtx} files 
+%     define encoding-specific commands.
+%   \item[\textsf{rsrccmd}]
+%     Similar to the \textsf{enccmds} module, but demonstrates the 
+%     |\New|\-|Describe|\-|Command| command instead.
+%   \item[\textsf{example}]
+%     This surrounds some code which to \package{docstrip} looks like it 
+%     should be copied, but isn't meant to.
+% \end{description}
+% 
+% 
+% 
+% \section{Initial stuff}
+% 
+% First there's the usual |\NeedsTeXFormat| and |\ProvidesPackage|.
+%    \begin{macrocode}
+%<*pkg>
+\NeedsTeXFormat{LaTeX2e}[1995/12/01]
+\ProvidesPackage{xdoc2}[2003/07/06 prot2.5 doc reimplementation package]
+%    \end{macrocode}
+% 
+% \subsection*{Options}
+% 
+% The first option has to do with the page layout. 
+% Although \package{doc} itself doesn't modify any of the main layout 
+% parameters, it is well known that using it does tend to restrict 
+% one's choices in terms of document layout. In particular the 
+% \texttt{macro} and \texttt{environment} environments require a rather 
+% large left margin since they will otherwise print long macro names 
+% partially outside the paper. It is furthermore hard to decrease the 
+% |\textwidth| as it should be wide enough to contain about 70 columns of 
+% |\MacroFont| text. Thus the only solution is to do as the 
+% \package{ltxdoc}~\cite{ltxdoc} document class and enlarge the left 
+% margin at the expense of the right. 
+% 
+% The resulting layout has a left--right asymmetry with the main galley 
+% (the text rectangle) on the right and a very wide left margin (in 
+% which marginal headings and marginal notes appears). Although this 
+% layout is not uncommon in technical manuals, it is inappropriate for 
+% two-sided designs since the vertical line at which the two pages of a 
+% spread meet becomes the natural vertical symmetry axis for the entire 
+% spread and it breaks this symmetry to let the left margin be the 
+% widest on all pages. It would look better to always let the outer 
+% margin be the largest.
+% 
+% \begin{option}{dolayout}
+% \begin{macro}{\oddsidemargin}
+%   The \texttt{dolayout} option modifies |\oddsidemargin| so that 
+%   spreads are symmetric around the center in two-sided mode. As size 
+%   of the outer margin is taken the size of the left margin on left 
+%   (even) pages, i.e., |\evensidemargin|${}+1\,\mathrm{in}$.
+%   
+%   In one-sided mode, the \texttt{dolayout} option does nothing.
+%    \begin{macrocode}
+\DeclareOption{dolayout}{%
+   \if@twoside
+      \setlength\oddsidemargin{\paperwidth}
+      \addtolength\oddsidemargin{-\textwidth}
+      \addtolength\oddsidemargin{-\evensidemargin}
+      \addtolength\oddsidemargin{-2in}
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}\end{option}
+% 
+% \begin{option}{olddocinclude}
+% \begin{option}{fileispart}
+%   The \texttt{olddocinclude} and \texttt{fileispart} options are 
+%   related to the |\DocInclude| command defined by the \package{ltxdoc} 
+%   document class. Some of the code related to that command relies on 
+%   modifying the \package{doc} internal macro |\codeline@wrindex|, but 
+%   that has no effect with \package{xdoc} so in order to get the 
+%   expected results one has to reimplement the |\DocInclude| command as 
+%   well. The \texttt{olddocinclude} and \texttt{fileispart} options 
+%   control how this should be done.
+%   
+%   If the \texttt{olddocinclude} option is passed to \package{xdoc} 
+%   then only the parts of the implementation of |\DocInclude| which 
+%   must be altered to make the command work with the \package{xdoc} 
+%   implementation of indexing and cross-referencing are changed. These 
+%   redefinitions will furthermore only be made if the \package{ltxdoc} 
+%   document class has been loaded; nothing is done if the 
+%   \texttt{olddocinclude} option is passed and \package{ltxdoc} hasn't 
+%   been loaded. Passing the \texttt{olddocinclude} option can be 
+%   considered as requesting a ``compatibility mode'' for |\DocInclude|.
+%   
+%   If the \texttt{olddocinclude} option is not passed then the 
+%   |\DocInclude| command is reimplemented from scratch, regardless of 
+%   whether some definition of it has already been given or not. The 
+%   basis of this reimplementation is the observation that the 
+%   |\DocInclude| command of \package{ltxdoc} really does two quite 
+%   distinct things at once---it is an |\include| command which 
+%   |\DocInput|s files rather than |\input|ting them, but it also starts 
+%   a new |\part|, sets the pagestyle, and changes how the values of 
+%   some counters are typeset. This latter function is by default 
+%   disabled in the \package{xdoc} implementation of |\DocInclude|, but 
+%   passing the \texttt{fileispart} option enables it.
+%   
+%   There is no code for these two options here, as it is rather long; 
+%   instead that code appears in Section~\ref{Sec:DocInclude}. The 
+%   |\Pass|\-|Options|\-|To|\-|Package| commands make sure that these 
+%   options are registered as local options for \package{xdoc}, so that 
+%   one can test for them using |\@if|\-|package|\-|with| below.
+%    \begin{macrocode}
+\DeclareOption{olddocinclude}{%
+   \PassOptionsToPackage{\CurrentOption}{xdoc2}%
+}
+\DeclareOption{fileispart}{%
+   \PassOptionsToPackage{\CurrentOption}{xdoc2}%
+}
+%    \end{macrocode}
+% \end{option}\end{option}
+%
+% \changes{prot2.5}{2003/07/06}{Reregeristing options in case
+%   they were global. (LH)}
+% 
+% \begin{option}{notrawchar}
+%   The \texttt{notrawchar} option controls how the |\PrintVisibleChar| 
+%   command is defined, and thereby what method is used for typesetting 
+%   visible characters in e.g.\ macro names. The default is to use the 
+%   |\char| primitive (which is better for \texttt{T1}-encoded fonts and 
+%   non-italic \texttt{OT1}-encoded typewriter fonts), but the 
+%   \texttt{notrawchar} option causes things to go via the ``\LaTeX\ 
+%   internal character representation'' instead (which is necessary 
+%   for e.g.\ \texttt{OT1}-encoded non-typewriter fonts).
+%   
+%   There is no code for this option here; instead that code is found 
+%   in the definition of |\Print|\-|Visible|\-|Char|.
+%    \begin{macrocode}
+\DeclareOption{notrawchar}{%
+   \PassOptionsToPackage{\CurrentOption}{xdoc2}%
+}
+%    \end{macrocode}
+% \end{option}
+% 
+% 
+% Then options are processed.
+%    \begin{macrocode}
+\ProcessOptions\relax
+%    \end{macrocode}
+% And finally the \package{doc} package is loaded.
+%    \begin{macrocode}
+\RequirePackage{doc}
+%    \end{macrocode}
+% 
+% 
+% \section{Character strings}
+% 
+% A source of much of the complexity in \package{doc} is that it has to 
+% be able to deal with rather arbitrary strings of characters (mainly 
+% the names of control sequences). Once the initial problems with 
+% characters having troublesome catcodes have been overcome however, it 
+% is usually no problem to manage such things in \TeX. \package{doc} 
+% does however complicate things considerably by also putting these 
+% things in the index and list of changes. Not only must they then be 
+% formatted so that the \package{makeindex} program doesn't choke on 
+% them, but they must also be wrapped up in code that allows \TeX\ to 
+% make sense of them when they are read back. \package{doc} manages the 
+% \package{makeindex} problems mainly by allowing the user to change what 
+% characters are used as \package{makeindex} metacharacters and the 
+% reading back problem by making abundant use of |\verb|.
+% 
+% All this relies on that the author of a document is making sure that 
+% the metacharacters aren't used for anything else. If for example the 
+% |\verbatimchar| (by default |+|) is one of the ``private letters'' 
+% then names of control sequences containing that character will be 
+% typeset incorrectly because the |\verb| used to typeset it is 
+% terminated prematurely---control sequence names such as `|\lost+found|' 
+% will be typeset as `|\lost|found+'. On top of that, one also has to 
+% make sure that the font used for typesetting these |\verb| sections 
+% contains all the characters needed.
+% 
+% For \package{xdoc}, I have chosen a completely different approach. 
+% Instead of allowing the strings (after they have converted to the 
+% internal format) to contain \TeX\ character tokens with arbitrary 
+% character codes, they may only contain \TeX\ character tokens which 
+% are unproblematic---the normal catcode should be 11 (letter) or 12 
+% (other), they should not be outside visible ASCII, and they may not 
+% be one of the \package{makeindex} metacharacters. All other characters 
+% are represented using a robust command which takes the character code 
+% (in decimal) as the argument. This takes care of all ``moving 
+% argument'' type problems that may occur.
+% 
+% An important observation about these character strings is that 
+% they are strings of \emph{input} characters. This means that rather 
+% than using the characters in some special font for typesetting 
+% control sequences like |\^^M| (recall that the |^^| substitutions 
+% take place before tokenization), one should typeset them using only 
+% visible ASCII characters. (After all, that's the only way they are 
+% written in \TeX\ code.) The default definition is to typeset 
+% invisible characters as precisely the |^^|-sequences that \TeX\ 
+% normally uses for these characters when they are written to a file.
+% 
+% 
+% \subsection{Typesetting problematic characters}
+% 
+% \begin{macro}{\PrintChar}
+% \begin{macro}{\XD@threedignum}
+%   The |\PrintChar| command has the syntax
+%   \begin{quote}
+%     |\PrintChar|\marg{8-bit number}
+%   \end{quote}
+%   where \meta{8-bit number} is a \TeX\ number in the range 0--255. 
+%   For arguments in the range 0--31, |\PrintChar| prints 
+%   `\textit{\ttfamily\string^\string^@}'--`\textit{\ttfamily
+%   \string^\string^\string_}'. For an argument in the range 32--126, 
+%   |\PrintChar| calls |\Print|\-|Visible|\-|Char| which by default 
+%   simply does |\char| on that argument (but which can be redefined 
+%   if the font set-up requires it); in particular, |\PrintChar{32}| 
+%   should print a ``visible space'' character. |\PrintChar{127}| prints 
+%   `\textit{\ttfamily\string^\string^?}'. For arguments in the range 
+%   128--255, |\PrintChar| prints 
+%   `\textit{\ttfamily\string^\string^80}'--`\textit{\ttfamily
+%   \string^\string^ff}'.
+%   
+%   |\PrintChar| is robust. |\PrintChar| also has a special behaviour 
+%   when it is written to a file (when |\protect| is |\noexpand|): it 
+%   makes sure that the argument consists of three decimal digits, to 
+%   ensure external sorting gets it right.
+%    \begin{macrocode}
+\@ifundefined{PrintChar}{}{%
+   \PackageInfo{xdoc2}{Redefining \protect\PrintChar}%
+}
+\def\PrintChar{%
+   \ifx \protect\@typeset@protect
+      \expandafter\XD@PrintChar
+   \else\ifx \protect\noexpand
+      \string\PrintChar
+      \expandafter\expandafter \expandafter\XD@threedignum
+   \else
+      \noexpand\PrintChar
+   \fi\fi
+}
+%    \end{macrocode}
+%   
+%   |\XD@threedignum| does a |\number| on its argument, possibly prepends 
+%   a |0| or two, and wraps it all up in a ``group'' (the braces have 
+%   category other, not beginning and end of group).
+%   \changes{prot2.1}{2000/11/15}{Braces inserted by 
+%      \cs{XD@threedignum} are given catcode other. (LH)}
+%    \begin{macrocode}
+\edef\XD@threedignum#1{%
+   \string{%
+   \noexpand\ifnum #1<100 %
+      \noexpand\ifnum #1<10 0\noexpand\fi
+      0%
+   \noexpand\fi
+   \noexpand\number#1%
+   \string}%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@PrintChar}
+% \begin{macro}{\InvisibleCharPrefix}
+% \begin{macro}{\InvisibleCharSuffix}
+%   |\XD@PrintChar| manages the typesetting for |\PrintChar|. It 
+%   distinguishes between visible characters (code 32--126) and 
+%   invisible characters. The visible characters are typeset directly 
+%   using |\PrintVisibleChar|, whereas the invisible characters are 
+%   typeset as |^^|-sequences.
+%   
+%   The macros |\InvisibleCharPrefix| and |\InvisibleCharSuffix| begin 
+%   and end a |^^|-sequence. |\InvisibleCharPrefix| should print the 
+%   actual |^^|, but it may also for example select a new font for 
+%   the |^^|-sequence (such font changes are restored at the end of 
+%   |\XD@PrintChar|).
+%    \begin{macrocode}
+\def\XD@PrintChar#1{%
+   \leavevmode
+   \begingroup
+      \count@=#1\relax
+      \ifnum \@xxxii>\count@
+         \advance \count@ 64%
+         \InvisibleCharPrefix
+         \PrintVisibleChar\count@
+         \InvisibleCharSuffix
+      \else\ifnum 127>\count@
+         \PrintVisibleChar\count@
+      \else
+         \InvisibleCharPrefix
+         \ifnum 127=\count@ \PrintVisibleChar{63}\else
+            \@tempcnta=\count@
+            \divide \count@ \sixt@@n
+            \@tempcntb=\count@
+            \multiply \count@ \sixt@@n
+            \advance \@tempcnta -\count@
+            \advance \@tempcntb \ifnum 9<\@tempcntb 87\else 48\fi
+            \advance \@tempcnta \ifnum 9<\@tempcnta 87\else 48\fi
+            \char\@tempcntb \char\@tempcnta
+         \fi
+         \InvisibleCharSuffix
+      \fi\fi
+   \endgroup
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\newcommand\InvisibleCharPrefix{%
+   \/\em
+   \PrintVisibleChar{`\^}\PrintVisibleChar{`\^}%
+}
+\newcommand\InvisibleCharSuffix{\/}
+%    \end{macrocode}
+%   There are some alternative methods for making hexadecimal numbers 
+%   which should perhaps be mentioned. The \LaTeX\ kernel contains a 
+%   macro |\hexnumber@| which uses |\ifcase| to produce one hexadecimal 
+%   digit, but that uses upper case letters, and things like `8E' look 
+%   extremely silly if the upper case letters doesn't line with the 
+%   digits. Applying |\meaning| to a \meta{chardef token} or 
+%   \meta{mathchardef token} expands to |\char"|\meta{hex} and 
+%   |\mathchar"|\meta{hex} respectively, where \meta{hex} is the 
+%   corresponding number in hexadecimal, but that too has upper case A--F 
+%   and leading zeros are removed.
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\PrintVisibleChar}
+%   \changes{prot2.1}{2000/12/18}{Made it possible to select the 
+%      alternative defintion of \cs{PrintVisibleChar} through an 
+%      \package{xdoc} package option. (LH)}
+%   The |\PrintVisibleChar| command should print the visible ASCII 
+%   character whose character code is given in the argument. There are 
+%   currently two definitions of this command: one which uses the \TeX\ 
+%   primitive |\char| and one which goes via the ``\LaTeX\ internal 
+%   character representation'' for the character. By default 
+%   \package{xdoc} uses the former definition, but if \package{xdoc} 
+%   is passed the 
+%   \SortIndex{notrawchar}{\texttt{notrawchar} option\encapchar usage}
+%   \texttt{notrawchar} option then it will use the latter.
+%   
+%   The reason there are two definitions is a deficiency in how the NFSS 
+%   encoding attribute has been assigned to fonts; even though the 
+%   encodings of Computer Modern Roman and Computer Modern Typewriter 
+%   are quite different, \LaTeXe\ uses the \texttt{OT1} encoding for 
+%   both. As a result of this, the \LaTeX\ internal representation will 
+%   in some important cases use characters from non-typewriter fonts 
+%   despite the fact that typewriter forms are immediately available.
+%   Since the cases in which the |\char| primitive produces results as 
+%   least as good as those made through the \LaTeX\ internal 
+%   character representation includes those that the current font is 
+%   \texttt{T1}-encoded or an \texttt{OT1}-encoded nonitalic typewriter 
+%   font, the shorter |\char| primitive defintion has been made the 
+%   default.
+%   
+%   For compability with prototype version~2.0 of \package{xdoc}, the 
+%   replacement text for |\Print|\-|Visible|\-|Char| that uses \LaTeX\ 
+%   internal character representation can alternatively be extracted by 
+%   \package{docstrip}ping \texttt{xdoc2.dtx} with the option 
+%   \Module{internals}.
+%    \begin{macrocode}
+\@ifpackagewith{xdoc2}{notrawchar}{%
+   \newcommand\PrintVisibleChar[1]{%
+%</pkg>
+%<*pkg|internals>
+      \ifcase #1%
+      \or\or\or\or\or\or\or\or \or\or\or\or\or\or\or\or 
+      \or\or\or\or\or\or\or\or \or\or\or\or\or\or\or\or
+      % "20
+         \textvisiblespace \or!\or\textquotedbl \or\#\or\textdollar 
+         \or\%\or\&\or\textquoteright\or(\or)\or*\or+\or,\or-\or.\or/%
+      \or % "30
+         0\or1\or2\or3\or4\or5\or6\or7\or8\or9\or:\or;\or
+         \textless\or=\or\textgreater\or?%
+      \or % "40
+         @\or A\or B\or C\or D\or E\or F\or G\or 
+         H\or I\or J\or K\or L\or M\or N\or O%
+      \or % "50
+         P\or Q\or R\or S\or T\or U\or V\or W\or X\or Y\or Z\or [\or
+         \textbackslash \or]\or\textasciicircum \or\textunderscore
+      \or % "60
+         \textquoteleft \or a\or b\or c\or d\or e\or f\or g\or h\or 
+         i\or j\or k\or l\or m\or n\or o%
+      \or % "70
+         p\or q\or r\or s\or t\or u\or v\or w\or x\or y\or z\or
+         \textbraceleft \or\textbar \or\textbraceright \or
+         \textasciitilde
+      \fi
+   }%
+%</pkg|internals>
+%<*pkg>
+}{%
+   \newcommand\PrintVisibleChar[1]{\char #1\relax}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \begin{macro}{\Bslash}
+%   It turns out that it is very common to say |\PrintChar{92}| 
+%   (backslash), so a macro which expands to that reduces typing.
+%    \begin{macrocode}
+\newcommand\Bslash{\PrintChar{92}}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \subsection{Rendering character strings harmless}
+% 
+% Replacing all problematic characters with |\PrintChar| calls certainly 
+% makes the strings easier to manage, but actually making those 
+% replacements is a rather complicated task. Therefore this subsection 
+% contains the macros necessary for doing these replacements.
+% 
+% The first problem is how to efficiently recognise the problematic 
+% characters. A first solution which gets rather far is to mainly look 
+% in the |\catcode| register for that character and keep the character 
+% as it is if the category found there is 11 or 12, but replace it with 
+% a |\PrintChar| command if the category is anything else. Two extra 
+% tests can be performed to take care of invisible ASCII, and the 
+% \package{makeindex} metacharacters can be cared for by locally 
+% changing their catcodes for when the string is processed. 
+% Unfortunately this doesn't work inside \texttt{macrocode} 
+% environments (where one would like to use it for the macro 
+% cross-referencing) since that environment changes the catcodes of 
+% several characters from being problematic to being unproblematic and 
+% vice versa.\footnote{As the entire \texttt{macrocode} environment is 
+% tokenized by the expansion of \cs{xmacro@code} one could alternatively 
+% solve this problem by reimplementing the \texttt{macrocode} 
+% environment so that normal catcodes are in force when the contents are 
+% being typeset.} As furthermore harmless character strings should be 
+% possible to move to completely different parts of the document, the 
+% test used for determining whether a character is problematic should 
+% yield the same result throughout the document.
+% 
+% Because of this, I have chosen a brute strength solution: build a 
+% table (indexed by character code) that gives the harmless form of 
+% every character. This table is stored in the
+% \describecsfamily{XD@harmless@\meta{code}}^^A
+% |\XD@harmless@|\meta{code} family of control sequences, where the 
+% \meta{code} is in the range |0|--|255|. Assignments to this table are 
+% global. In principle, the table should not change after the preamble, 
+% but there is a command |\SetHarmState| which can be used at any time 
+% for setting a single table entry. This could be useful for documents 
+% which, like for example~\cite{fontinst}, have nonstandard settings of 
+% |\catcode|s.
+% 
+% \begin{macro}{\SetHarmState}
+%   The |\SetHarmState| command takes three arguments:
+%   \begin{quote}
+%     |\SetHarmState|\marg{type}\marg{char}\marg{harm}
+%   \end{quote}
+%   \meta{char} is the character whose entry should be set. \meta{type} 
+%   is a flag which specifies what format \meta{char} is given in. If 
+%   \meta{type} is |\BooleanTrue| then \meta{char} is the \TeX\ 
+%   \meta{number} of the table entry to set, and if \meta{type} is 
+%   |\BooleanFalse| then \meta{char} is something which expands to a 
+%   single character token whose entry should be set. The expansion is 
+%   carried out by an |\edef|, so it needs not be only one level. 
+%   \meta{harm} is |\BooleanTrue| if the character is problematic and 
+%   |\BooleanFalse| if it is not.
+%   
+%   The \meta{type} and \meta{harm} arguments are currently not subject 
+%   to any expansion. In the future they probably should be, but I 
+%   don't want to make assumptions about the actual definitions of 
+%   |\BooleanTrue| and |\BooleanFalse| at this point.
+%    \begin{macrocode}
+\begingroup
+   \catcode\z@=12
+   \@ifdefinable\SetHarmState{
+      \gdef\SetHarmState#1#2#3{%
+         \begingroup
+            \ifx #1\BooleanTrue
+               \count@=#2\relax
+            \else
+               \protected@edef\@tempa{#2}%
+               \count@=\expandafter`\@tempa\relax
+            \fi
+            \ifx #3\BooleanTrue
+               \edef\@tempa{\noexpand\PrintChar{\the\count@}}%
+            \else
+               \uccode\z@=\count@
+               \uppercase{\def\@tempa{^^@}}%
+            \fi
+            \global\expandafter\let
+               \csname XD@harmless@\the\count@ \endcsname \@tempa
+         \endgroup
+      }%
+   }
+\endgroup
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{trivlist}\item[]\leavevmode ^^A Just for the look of it
+%   \GenericDescribePrint{\small\cs{XD@harmless@}\meta{code}}^^A
+%   ^^A There should have been a "main" index entry here as well,
+%   ^^A but generating that with \package{doc} commands is more than I 
+%   ^^A bother to do right now.
+%   Initializing the |\XD@harmless@|\meta{code} table is a 
+%   straightforward exercise of |\loop| \dots\ |\repeat|.
+%    \begin{macrocode}
+%<*!economical>
+\count@=\z@
+\loop
+   \expandafter\xdef \csname XD@harmless@\the\count@ \endcsname
+      {\noexpand\PrintChar{\the\count@}}%
+   \advance \count@ \@ne
+\ifnum 33>\count@ \repeat
+%</!economical>
+%<economical>\count@=\@xxxii
+\begingroup
+   \catcode\z@=12\relax
+   \@firstofone{%
+\endgroup
+   \loop
+      \if \ifnum 11=\catcode\count@ 1\else \ifnum 12=\catcode\count@
+            1\else 0\fi\fi 1%
+         \uccode\z@=\count@
+         \uppercase{\def\@tempa{^^@}}%
+      \else
+         \edef\@tempa{\noexpand\PrintChar{\the\count@}}%
+      \fi
+      \global\expandafter\let
+         \csname XD@harmless@\the\count@ \endcsname \@tempa
+      \advance \count@ \@ne
+   \ifnum 127>\count@ \repeat
+}
+%<*!economical>
+\loop
+   \expandafter\xdef \csname XD@harmless@\the\count@ \endcsname
+      {\noexpand\PrintChar{\the\count@}}%
+\ifnum \@cclv>\count@ 
+   \advance \count@ \@ne
+\repeat
+%</!economical>
+%    \end{macrocode}
+%   Marking the \package{makeindex} metacharacters as harmful is 
+%   deferred until |\begin|\nolinebreak[2]|{document}|, since it is not 
+%   unreasonable that these are changed in the preamble.
+%    \begin{macrocode}
+\AtBeginDocument{%
+   \SetHarmState\BooleanFalse\actualchar\BooleanTrue
+   \SetHarmState\BooleanFalse\encapchar\BooleanTrue
+   \SetHarmState\BooleanFalse\levelchar\BooleanTrue
+   \SetHarmState\BooleanFalse\quotechar\BooleanTrue
+}
+%    \end{macrocode}
+%   \package{doc}'s |\verbatimchar| is not harmful, since it isn't used 
+%   at all in \package{xdoc}.
+% \end{trivlist}
+% 
+% 
+% \begin{macro}{\MakeHarmless}
+%   To render a character string harmless, you do
+%   \begin{quote}
+%     |\MakeHarmless|\marg{macro}\marg{string}
+%   \end{quote}
+%   This locally assigns to \meta{macro} the harmless character string 
+%   which corresponds to \meta{string}. During the conversion the converted 
+%   part of the string is stored in |\toks@|, but that is local to 
+%   |\MakeHarmless|.
+%    \begin{macrocode}
+\def\MakeHarmless#1#2{%
+   \begingroup
+      \toks@={}%
+      \escapechar=`\\%
+      \XD@harmless@#2\XD@harmless@
+   \expandafter\endgroup \expandafter\def \expandafter#1%
+      \expandafter{\the\toks@}%
+}
+%    \end{macrocode}
+% 
+% \begin{macro}{\XD@harmless@iii}
+% \begin{macro}{\XD@harmless@iv}
+% \begin{macro}{\XD@harmless@v}
+%   \changes{prot2}{2000/07/27}{Moved code for adding to \cs{toks@} here 
+%      and changed it to append the contents of \cs{XD@harmless@32}, not 
+%      necessarily a \cs{PrintChar}. (LH)}
+% \begin{macro}{\XD@harmless@vi}
+%   What one has to be most careful about when rendering strings 
+%   harmless are the space tokens, since many of \TeX's primitives gladly 
+%   snatches an extra space (or more) where you don't want them to in 
+%   this case. Macro parameters can be particularly dangerous, as \TeX\ 
+%   will skip any number of spaces while looking for the replacement 
+%   text for an undelimited macro argument. Therefore the algorithm for 
+%   rendering a character token harmless begins 
+%   (|\XD@|\B|harmless@iii|) with |\string|ing the next token in the 
+%   string---this preserves the character code and sets the category to 
+%   12 for all characters except the ASCII space, which gets category 10 
+%   (space)---and then |\futurelet| is used to peek at the next token. If 
+%   it is a space token (|\XD@|\B|harmless@iv|) then the character code 
+%   is 32 and the actual space can be gobbled (|\XD@|\B|harmless@v|), and 
+%   if it isn't then the next token can be grabbed in an undelimited macro 
+%   argument (|\XD@|\B|harmless@vi|). In either case, the harmless form 
+%   is given by the |\XD@|\B|harmless@|\meta{code} table entry 
+%   (in |\XD@|\B|harmless@v| or |\XD@|\B|harmless@vi|).
+%    \begin{macrocode}  
+\def\XD@harmless@iii{%
+   \expandafter\futurelet \expandafter\@let@token 
+   \expandafter\XD@harmless@iv \string
+}
+%    \end{macrocode}  
+%    \begin{macrocode}  
+\def\XD@harmless@iv{%
+   \ifx \@let@token\@sptoken
+      \expandafter\XD@harmless@v
+   \else
+      \expandafter\XD@harmless@vi
+   \fi
+}
+%    \end{macrocode}
+%   ^^A Hack:
+%   \begingroup
+%   \expandafter\def \expandafter\MakePrivateLetters \expandafter{^^A
+%      \MakePrivateLetters
+%      \catcode`3=11
+%      \catcode`2=11
+%   }
+%    \begin{macrocode}
+\begingroup
+   \catcode`3=\catcode`a
+   \catcode`2=\catcode`a
+   \@firstofone{\gdef\XD@harmless@v} {%
+      \toks@=\expandafter{\the \expandafter\toks@ \XD@harmless@32}%
+      \XD@harmless@
+   }
+\endgroup
+%    \end{macrocode}
+%   \endgroup
+%   In the \Module{economical} (with hash table space) variant 
+%   implementation the |\XD@harmless@|\meta{code} table has entries only 
+%   for the characters in visible ASCII. Thus the harmless forms of 
+%   characters outside visible ASCII must be constructed on the fly.
+%    \begin{macrocode}  
+\def\XD@harmless@vi#1{%
+%<*economical>
+   \if \ifnum `#1<\@xxxii 1\else \ifnum `#1>126 1\else 0\fi\fi 1%
+      \toks@=\expandafter{\the\expandafter\toks@
+         \expandafter\PrintChar \expandafter{\number`#1}%
+      }%
+   \else
+%</economical>   
+   \toks@=\expandafter{\the\expandafter\expandafter\expandafter\toks@
+      \csname XD@harmless@\number`#1\endcsname}%
+%<economical>   \fi
+   \XD@harmless@
+}
+%    \end{macrocode}  
+% \end{macro}\end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@harmless@}
+% \begin{macro}{\XD@harmless@i}
+% \begin{macro}{\XD@harmless@ii}
+%   But that is not all |\MakeHarmless| can do. In some cases (as for 
+%   example when one is describing a family of control sequences) one 
+%   might want to include things in the string that are not simply 
+%   characters, but more complex items---such as for example |\meta| 
+%   constructions like \meta{code}. To accommodate for this, 
+%   |\XD@harmless@| (which is the first step in converting a token) 
+%   always begins by checking whether the next token to render harmless 
+%   is a control sequence. If it is then it is checked (in 
+%   |\XD@harmless@ii|) whether the control sequence 
+%   \describecsfamily{XD@harmless\Bslash\meta{cs-name}}^^A
+%   |\XD@harmless\|\meta{cs-name}, where \meta{cs-name} is the name 
+%   without |\| of the control sequence encountered, is defined. If it 
+%   isn't then the encountered control sequence is |\string|ed and 
+%   conversion continues as above, but if it is defined then the 
+%   encountered control sequence begins such a more complex item.
+%    \begin{macrocode}
+\def\XD@harmless@{\futurelet\@let@token \XD@harmless@i}
+%    \end{macrocode}  
+%    \begin{macrocode}
+\def\XD@harmless@i{%
+   \ifcat \noexpand\@let@token \noexpand\XD@harmless@
+      \expandafter\XD@harmless@ii
+   \else
+      \expandafter\XD@harmless@iii
+   \fi
+}
+%    \end{macrocode}  
+%    \begin{macrocode}
+\def\XD@harmless@ii#1{%
+   \@ifundefined{XD@harmless\string#1}{%
+      \expandafter\XD@harmless@vi \string#1%
+   }{\csname XD@harmless\string#1\endcsname}%
+}
+%    \end{macrocode}  
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@harmless\XD@harmless@}
+%   A control sequence |\XD@harmless\|\meta{cs-name} is responsible for 
+%   interpreting the string item that begins with the control sequence 
+%   |\|\meta{cs-name} and appending a harmless representation of it to 
+%   |\toks@|. Harmless representations should only contain robust 
+%   control sequences and they must not rely on changing any catcodes. 
+%   Normal |\XD@harmless\|\meta{cs-name} control sequences must also 
+%   end by inserting |\XD@harmless@| in front of what remains of the 
+%   string after the complex string item has been removed. This sees to 
+%   that the rest of the string is also rendered harmless. The only such
+%   control sequence which does not insert |\XD@harmless@| is 
+%   |\XD@harmless\XD@harmless@|, but that is as it should be since 
+%   |\MakeHarmless| itself appends a |\XD@harmless@| to every character 
+%   string it should convert to mark the end of it.
+%    \begin{macrocode}
+\expandafter\let 
+   \csname XD@harmless\string\XD@harmless@\endcsname \@empty
+%    \end{macrocode}
+% \end{macro}
+% \end{macro}
+% 
+% \begin{macro}{\XD@harmless\PrintChar}
+%   It is occasionally convenient to use a |\PrintChar| command as part 
+%   of a string that is to be rendered harmless instead of using the raw 
+%   character. The definition is very similar to that of 
+%   |\XD@harmless@vi|.
+%    \begin{macrocode}  
+\@namedef{XD@harmless\string\PrintChar}#1{%
+%<*economical>
+   \if \ifnum #1<\@xxxii 1\else \ifnum #1>126 1\else 0\fi\fi 1%
+      \toks@=\expandafter{\the\expandafter\toks@
+         \expandafter\PrintChar \expandafter{\number#1}%
+      }%
+   \else
+%</economical>   
+   \toks@=\expandafter{\the\expandafter\expandafter\expandafter\toks@
+      \csname XD@harmless@\number#1\endcsname}%
+%<economical>   \fi
+   \XD@harmless@
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \subsection{Interaction with mechanisms that make characters 
+%    problematic}
+% 
+% If additional visible characters are made problematic after the 
+% initial |\XD@harmless@|\meta{code} table is formed then problems may 
+% indeed arise, because some character which is expected to be 
+% unproblematic when read from (for example) an \texttt{.ind} file will 
+% actually not be. In fortunate cases this will only lead to that 
+% characters will print strangely or not at all, but it can quite 
+% conceivably lead to errors that prevent further typesetting and it 
+% should therefore be prevented if possible.
+% 
+% Right now, I can think of two mechanisms that make characters 
+% problematic, and both do that by making them active. One is the 
+% shorthand mechanism of \package{babel}, but I think I'll delay 
+% implementing any interaction with that until some later prototype; I 
+% don't know it well enough and anyway I don't think it is that likely 
+% to cause any problems. The other mechanism is the short verb mechanism 
+% of \package{doc} itself, and this should be taken care of right away.
+% 
+% The main difficulty is that the |\XD@harmless@|\meta{code} table should 
+% be the same throughout the document body (otherwise you may get more 
+% than one index entry for the same thing, with index references 
+% arbitrarily distributed between the two) whereas short verb characters 
+% can be made and deleted at any time. It would actually be wrong to 
+% always have the |\XD@harmless@|\meta{code} table entry mirroring the 
+% current state of the character! Instead a character will be considered 
+% as problematic even if it is only made problematic temporarily (with 
+% the exception for characters that are made problematic in 
+% \texttt{verbatim} environments and the like---the index file isn't 
+% being read in while those catcodes are active). Since it is impossible 
+% to know in the beginning of a document whether a character will be made 
+% a short verb character at some later point, the modifications to the 
+% |\XD@harmless@|\meta{code} table that will be made because of short verb 
+% characters will (at least partially) be based on which characters were 
+% made short verbs on the previous run.
+% 
+% \begin{macro}{\SetCharProblematic}
+%   \changes{prot2}{2000/07/26}{Command added. (LH)}
+%   The |\SetCharProblematic| command should be called by commands which 
+%   make a character problematic (e.g.\ makes it active) in the general 
+%   context (commands which make some character problematic only in some 
+%   very special context, such as the \texttt{verbatim} environment, 
+%   need not call |\Set|\-|Char|\-|Problematic|). The syntax is
+%   \begin{quote}
+%     |\SetCharProblematic|\marg{code}
+%   \end{quote}
+%   and it sets the ``harm state'' of the character whose code is 
+%   \meta{code} to problematic.
+%   
+%   When |\SetCharProblematic| is called in the preamble, it sets the 
+%   harm state on the current run. When it is called in the document 
+%   body however, it sets the harm state on the next run by writing a 
+%   |\SetHarmState| command to the \texttt{.aux} file. This is done to 
+%   ensure that the contents of the |\XD@harmless@|\meta{code} table 
+%   doesn't change during the body of a document.
+%    \begin{macrocode}
+\newcommand\SetCharProblematic[1]{%
+   \SetHarmState\BooleanTrue{#1}\BooleanTrue
+}
+\AtBeginDocument{%
+   \gdef\SetCharProblematic#1{%
+      \if@filesw
+         \immediate\write\@auxout{\string\SetHarmState 
+            \string\BooleanTrue {\number#1}\string\BooleanTrue}%
+      \fi
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\add@specials}
+%   \changes{prot2}{2000/07/26}{Redefinition added. (LH)}
+%   |\MakeShortVerb|'s call to |\SetCharProblematic| is put in the 
+%   |\add@|\B|specials| macro, which anyway already adds the character 
+%   to the |\dospecials| and |\@sanitize| lists. Only familiar 
+%   definitions of |\add@special| are changed.
+%    \begin{macrocode}
+\def\@tempa#1{%
+  \rem@special{#1}%
+  \expandafter\gdef\expandafter\dospecials\expandafter
+    {\dospecials \do #1}%
+  \expandafter\gdef\expandafter\@sanitize\expandafter
+    {\@sanitize \@makeother #1}}
+\ifx \@tempa\add@special
+   \def\add@special#1{%
+      \rem@special{#1}%
+      \expandafter\gdef\expandafter\dospecials\expandafter
+         {\dospecials \do #1}%
+      \expandafter\gdef\expandafter\@sanitize\expandafter
+         {\@sanitize \@makeother #1}%
+      \SetCharProblematic{`#1}%
+   }
+\else
+   \PackageWarningNoLine{xdoc2}{Unfamiliar definition of 
+      \protect\add@special;\MessageBreak the macro was not patched}
+\fi
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% 
+% \section{Indexing}
+% \label{Sec:Indexing}
+% 
+% Each type of index entry \package{doc} produces is implemented through 
+% a different indexing command.\footnote{Sometimes there are 
+% even more than one command per entry type---the \cs{SpecialIndex}, 
+% \cs{LeftBraceIndex}, \cs{RightBraceIndex}, and \cs{PercentIndex} 
+% commands all generate entries of the same type.} This might be 
+% manageable when there are only \texttt{macro}s and 
+% \texttt{environment}s to distinguish between, but it soon gets 
+% unmanageable if more environments of this type are added. Therefore 
+% all \package{xdoc} index entries are made with a single 
+% command---|\IndexEntry|.
+% 
+% 
+% \subsection{New basic indexing commands}
+% \label{Ssec:IndexEntry}
+% 
+% \begin{macro}{\IndexEntry}
+% \begin{macro}{\LevelSame}
+%   \changes{prot2.1}{2000/11/18}{New name for \cs{levelsame}. (LH)}
+% \begin{macro}{\LevelSorted}
+%   \changes{prot2.1}{2000/11/18}{New name for \cs{levelsorted}. (LH)}
+% \begin{macro}{\XD@if@index}
+%   The |\IndexEntry| command writes one index entry to the \texttt{.idx} 
+%   file. It takes three arguments:
+%   \begin{quote}
+%     |\IndexEntry|\marg{entry text}\marg{encap}\marg{thenumber}
+%   \end{quote}
+%   The \meta{entry text} contains the text for the entry. It is a 
+%   nonempty sequence of commands in which each item is one of
+%   \begin{quote}
+%     |\LevelSame|\marg{text}\\
+%     |\LevelSorted|\marg{sort key}\marg{text}
+%   \end{quote}
+%   Each such item specifies one level of the entry that is to be 
+%   written. In the case of |\LevelSorted|, the \meta{text} is what will 
+%   be written in the sorted index at that level and \meta{sort key} is 
+%   a key which the index-sorting program should use for sorting that 
+%   entry at that level. In the case of |\LevelSame|, the \meta{text} is 
+%   used both as sort key and contents of entry in the sorted index.
+%   The first item is for the topmost level and each subsequent item is 
+%   for the next sublevel. The \meta{entry text} will be fully expanded 
+%   by the |\IndexEntry| command.
+%   
+%   \meta{thenumber} is the number (if any) that the index entry refers 
+%   to. It can consist of explicit characters, but it can also be a 
+%   |\the|\meta{counter} control sequence or a macro containing such 
+%   control sequences. \meta{thenumber} is fully expanded by the 
+%   |\IndexEntry| command, with the exception for occurrences of 
+%   |\thepage|---expansion of |\thepage| will instead be delayed until 
+%   the page is shipped out, so that the page numbers will be right. 
+%   \textbf{Note:} \meta{thenumber} must not contain any formatting that 
+%   will upset the index-sorting program. \package{doc}'s default 
+%   definition of |\theCodelineNo| contains such formatting, so one 
+%   must instead use |\thecodelineno| as \meta{thenumber} in that case.
+%   
+%   \meta{encap} is the name of the encapsulation scheme that should be 
+%   applied to \meta{thenumber}. All encapsulation schemes that have been 
+%   implemented instruct the index sorting program to wrap up 
+%   \meta{thenumber} in some code that gives it special formatting when 
+%   the sorted index is written, but one could also use the \meta{encap} 
+%   to specify `beginning of range' and `end of range' index entries. 
+%   Use \GenericDescribePrint{\small\texttt{none}}^^A
+%   \SortIndex{none}{\texttt{none}\encapchar usage}\texttt{none} as 
+%   \meta{encap} if you don't want any special formatting.
+%   
+%   \textbf{Note:} |\IndexEntry| uses |\@tempa| internally, so you 
+%   cannot use that in argument \#2 or \#3. Using it in argument \#1 
+%   presents no problems, though.
+%    \begin{macrocode}
+\newcommand\IndexEntry[3]{%
+   \@bsphack
+   \begingroup
+      \def\LevelSame##1{\levelchar##1}%
+      \def\LevelSorted##1##2{\levelchar##1\actualchar##2}%
+      \protected@edef\@tempa{#1}%
+      \protected@edef\@tempa{\expandafter\@gobble\@tempa\@empty}%
+      \@ifundefined{XD@idxencap@#2}{%
+         \PackageError{xdoc2}{Index entry encap `#2' unknown}\@eha
+      }{%
+         \XD@if@index{%
+            \csname XD@idxencap@#2\endcsname\@tempa{#3}%
+         }{}%
+      }%
+   \endgroup
+   \@esphack
+}
+%    \end{macrocode}
+%   |\IndexEntry| does (like |\index|) not contribute any material to the 
+%   current list if indices aren't being made.
+%   
+%   |\XD@if@index| is |\@firstoftwo| if index entries are being written 
+%   and |\@second|\-|of|\-|two| if they are not.
+%    \begin{macrocode}
+\let\XD@if@index=\@secondoftwo
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}\end{macro}
+% 
+% In \LaTeXplus, the \cs{IndexEntry} command should probably be 
+% implemented using templates, e.g. the \meta{encap}s could be names of 
+% instances.
+% 
+% \begin{macro}{\levelsame}
+% \begin{macro}{\levelsorted}
+%   These names were used for |\LevelSame| and |\LevelSorted| 
+%   respectively in prototype version~2.0, but the macros should belong 
+%   to the same capitalization class as |\IndexEntry| so their names 
+%   were changed in prototype version~2.1. The old names |\levelsame| 
+%   and |\levelsorted| will continue to work in \package{xdoc2}, though.
+%    \begin{macrocode}
+%<*xdoc2>
+\newcommand*\levelsame{\LevelSame}
+\newcommand*\levelsorted{\LevelSorted}
+%</xdoc2>
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \describecsfamily{XD@idxencap@\meta{encap}}^^A
+% Macros in the family |\XD@idxencap@|\meta{encap} takes two 
+% arguments as follows
+% \begin{quote}
+%   |\XD@idxencap@|\meta{encap}\,\marg{entry}\,\marg{thenumber}
+% \end{quote}
+% They should write an entry with the \meta{encap} encapsulation of the 
+% \meta{thenumber} to the index file. They need not check whether index 
+% generation is on or not, but they must be subject to the \LaTeX\ kernel 
+% \texttt{@filesw} switch. They must expand both arguments fully at the 
+% time of the command, with the exception for the control sequence 
+% |\thepage|, which should not be expanded until the page on which the 
+% write appears is output. Both these conditions are met if the macro 
+% is implemented using |\protected@write|.
+% 
+% \begin{macro}{\XD@idxencap@none}
+% \begin{macro}{\XD@idxencap@main}
+% \begin{macro}{\XD@idxencap@usage}
+%   These macros implement the encapsulation schemes that are used in 
+%   \package{doc}.
+%    \begin{macrocode}
+\def\XD@idxencap@none#1#2{%
+   \protected@write\@indexfile{}{\XD@index@keyword{#1}{#2}}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\XD@idxencap@main#1#2{%
+   \protected@write\@indexfile{}%
+      {\XD@index@keyword{#1\encapchar main}{#2}}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\XD@idxencap@usage#1#2{%
+   \protected@write\@indexfile{}%
+      {\XD@index@keyword{#1\encapchar usage}{#2}}%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@index@keyword}
+%   \changes{prot2.2}{2001/02/13}{Macro added and \meta{encap} macros 
+%      changed to use it. (LH)}
+%   The |\XD@index@keyword| is a hook for changing the index entry 
+%   keyword (the text that is put in front of every index entry in the 
+%   \texttt{.idx} file). It is changed by e.g.\ the \package{docindex} 
+%   package~\cite{docindex}.
+%    \begin{macrocode}
+\@ifundefined{XD@index@keyword}{%
+   \edef\XD@index@keyword{\@backslashchar indexentry}%
+}{}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\CodelineIndex}
+%   \changes{prot2.1}{2000/10/08}{Using \cs{thecodelineno}. (LH)}
+% \begin{macro}{\PageIndex}
+% \begin{macro}{\TheXDIndexNumber}
+%   The |\CodelineIndex| and |\PageIndex| commands do the same things as 
+%   in \package{doc}, but work with the \package{xdoc} internals instead 
+%   of the \package{doc} ones. |\TheXDIndexNumber| is used as 
+%   \meta{thenumber} argument to |\IndexEntry| by all indexing commands 
+%   that would have used |\special@index| in \package{doc}.
+%    \begin{macrocode}
+\renewcommand\CodelineIndex{%
+   \makeindex
+   \let\XD@if@index=\@firstoftwo
+   \codeline@indextrue
+   \def\TheXDIndexNumber{\thecodelineno}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\renewcommand\PageIndex{%
+   \makeindex
+   \let\XD@if@index=\@firstoftwo
+   \codeline@indexfalse
+   \def\TheXDIndexNumber{\thepage}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\TheXDIndexNumber{??}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% 
+% \subsection{Making good sort keys}
+% 
+% \changes{prot2.1}{2000/11/15}{Sort key making commands added. (LH)}
+% A common nuisance in \package{doc} indices is that many macros are 
+% sorted by parts of the name that do not carry any interesting 
+% information. In the \LaTeX\ kernel many macro names begin with a 
+% silent |@|, whereas the names of private macros in many packages 
+% (including this one) begin with some fixed abbreviation of the 
+% package name. Since such prefixes usually are harder to remember than 
+% the rest of the macro name, it is not uncommon that the index position 
+% one thinks of first isn't the one where the macro actually is put. 
+% Hence a mechanism for removing such annoying prefixes from the macro 
+% names might be useful, and that is presicely what is defined below.
+% 
+% The actual mechanism is based on having a set of macros called 
+% \emph{operators} which operate on the harmless character string that 
+% is to become the sort key. Each operator has a specific prefix string 
+% which it tries to match against the beginning of the to-be sort key, 
+% and if they match then the prefix is moved to the end of the sort key. 
+% Automatically constructed operators (see below) have names of the form 
+% \describecsfamily{XD@operatorA@\meta{prefix}}|\XD@operatorA@|^^A
+% \meta{prefix}, but operators can be given arbitrary names.
+% 
+% \begin{macro}{\XD@operators@list}
+%   The |\XD@operators@list| macro contains the list of all currently 
+%   active operators.
+%    \begin{macrocode}
+\let\XD@operators@list\@empty
+%    \end{macrocode}
+% \end{macro}
+% 
+% The operators do all their work at expand-time. When an operator 
+% macro is expanded, it is in the context
+% \begin{quote}
+%   \meta{operator} \meta{subsequent operators} |\@firstofone|
+%   \meta{sort key text} |\@empty|
+% \end{quote}
+% There may not be any |\@empty|s or |\@firstofone|s amongst the 
+% \meta{subsequent operators} or in the \meta{sort key text}. This should 
+% expand to
+% \begin{quote}
+%   \meta{subsequent operators} |\@firstofone| \meta{operated-on sort 
+%   key text} |\@empty|
+% \end{quote}
+% The purpose of the |\@firstofone| after the \meta{subsequent 
+% operators} is to remove any spaces that some operator might have put 
+% in front of the sort key. This happens if the entire sort key text has 
+% been ignored by some operator.
+% 
+% \begin{macro}{\MakeSortKey}
+%   The |\MakeSortKey| command is called to make the acutal sort key. 
+%   The syntax of this command is
+%   \begin{quote}
+%     |\MakeSortKey|\marg{macro}\marg{text}\marg{extras}
+%   \end{quote}
+%   This locally defines \meta{macro} to be the sort key that the 
+%   currently active operators manufacture from \meta{text}. The 
+%   \meta{extras} argument can contain additional assignments needed for 
+%   handling macros with special harmless forms, such as |\meta|.
+%    \begin{macrocode}
+\newcommand\MakeSortKey[3]{%
+   \begingroup
+      \def\PrintChar{\string\PrintChar\XD@threedignum}%
+      #3%
+      \unrestored@protected@xdef\@gtempa{#2}%
+   \endgroup
+   \protected@edef#1{%
+      \expandafter\XD@operators@list \expandafter\@firstofone 
+      \@gtempa\@empty
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\XD@make@operator}
+%   The |\XD@make@operator| macro takes a harmless character sequence as 
+%   argument, constructs the corresponding operator, and returns the 
+%   operator control sequence in the |\toks@| token list register.
+%   
+%   More precisely, given a harmless character string \meta{string}, 
+%   |\XD@make@operator| will construct a sequence of other tokens 
+%   \meta{text} from \meta{string} by replacing all |\PrintChar| 
+%   commands in the same way as |\MakeSortKey| does. Then it defines the 
+%   macro |\XD@operatorA@|\meta{text} to be
+%   \begin{quote}
+%     \raggedright \spaceskip=0.16666em
+%     \#1\,|\@firstofone|\,\#2\,|\@empty| \ $\rightarrow$ \ %
+%     |\XD@operatorB@|\meta{text} |\@firstofone| \#2 
+%     |\@firstofone| \meta{text} |\@firstofone| |\relax| \#1 |\@empty|
+%   \end{quote}
+%   and the macro |\XD@operatorB@|\meta{text} to do
+%   \begin{quote}
+%     \raggedright
+%     \#1\,|\@firstofone|\,\meta{text}\,\#2\,|\@firstofone|\,\#3\,^^A
+%     |\relax|\,\#4\,|\@empty| $\rightarrow$ 
+%     \#4\,\( \left\{ \begin{array}{ll} 
+%     \mbox{\cs{@firstofone}\,\#2\,\textvisiblespace\,\meta{text}\,^^A
+%     \cs{@empty}}& \mbox{if \#1 is empty}\\ 
+%     \mbox{\#1\,\cs{@empty}}& \mbox{otherwise}
+%     \end{array} \right.\)
+%   \end{quote}
+%   
+%    \begin{macrocode}
+\def\XD@make@operator#1{%
+   \begingroup
+      \def\PrintChar{\string\PrintChar\XD@threedignum}%
+      \let\protect\@gobble
+      \xdef\@gtempa{#1}%
+   \endgroup
+   \expandafter\edef \csname XD@operatorA@\@gtempa\endcsname
+      ##1\@firstofone##2\@empty{%
+      \expandafter\noexpand \csname XD@operatorB@\@gtempa\endcsname
+      \noexpand\@firstofone ##2\noexpand\@firstofone \@gtempa
+      \noexpand\@firstofone \relax##1\noexpand\@empty
+   }%
+   \expandafter\edef \csname XD@operatorB@\@gtempa \expandafter\endcsname
+      \expandafter##\expandafter1\expandafter\@firstofone \@gtempa
+      ##2\@firstofone##3\relax##4\@empty{%
+      \noexpand\ifx $##1$%
+         \noexpand\expandafter \noexpand\@firstoftwo
+      \noexpand\else
+         \noexpand\expandafter \noexpand\@secondoftwo
+      \noexpand\fi{%
+         ##4\noexpand\@firstofone ##2 \@gtempa
+      }{##4##1}%
+      \noexpand\@empty
+   }%
+   \toks@=\expandafter{\csname XD@operatorA@\@gtempa\endcsname}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\DoNotIndexBy}
+%   The |\DoNotIndexBy| command has the syntax
+%   \begin{quote}
+%     |\DoNotIndexBy|\marg{morpheme}
+%   \end{quote}
+%   It causes the \meta{morpheme} to be put \emph{last} in the index 
+%   sort key for each macro name which begins by \meta{morpheme}. This 
+%   can be used to ignore e.g.\ ``silent'' |@|s at the beginning of a 
+%   macro name.
+%    \begin{macrocode}
+\newcommand\DoNotIndexBy[1]{%
+   \MakeHarmless\@tempa{#1}%
+   \XD@make@operator\@tempa
+   \expandafter\def \expandafter\XD@operators@list \expandafter{%
+      \the\expandafter\toks@ \XD@operators@list
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+%   
+% 
+% 
+% \subsection{Reimplementations of \package{doc} indexing commands}
+% 
+% The \package{doc} indexing commands aren't that interesting in 
+% \package{xdoc}, since they take `raw' control sequences as 
+% arguments rather than the harmless strings that the \package{xdoc} 
+% commands will want to put in the index. But it can be instructive to 
+% see how they would be implemented in this context.
+% 
+% \begin{macro}{\SortIndex}
+%   \changes{prot2.2}{2001/02/13}{Redefinition added. (LH)}
+%   The |\SortIndex| takes a sort key and an entry text as argument, and 
+%   writes a one-level index entry for that.
+%    \begin{macrocode}
+\renewcommand*\SortIndex[2]{%
+   \IndexEntry{\LevelSorted{#1}{#2}}{none}{\thepage}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\SpecialIndex}
+% \begin{macro}{\SpecialMainIndex}
+% \begin{macro}{\SpecialUsageIndex}
+%   The |\SpecialIndex|, |\SpecialMainIndex|, and |\SpecialUsageIndex| 
+%   commands take a control sequence (or more often something which looks 
+%   like a |\string|ed control sequence) as their only argument. The 
+%   entry text is that item verbatim, and the initial backslash is 
+%   ignored in sorting (|\Special|\-|Index| always ignores the first 
+%   character regardless of whether it is a backslash or not, the other 
+%   two checks first). |\Special|\-|Index| has \texttt{none} formatting, 
+%   |\Special|\-|Main|\-|Index| has \texttt{main} formatting, and 
+%   |\Special|\-|Usage|\-|Index| has \texttt{usage} formatting of the 
+%   index number.
+%   
+%   Although these definitions will (or at least are supposed to) yield 
+%   the same typeset results as the \package{doc} definitions in the 
+%   mainstream cases, I doubt that they will do so in all cases. At any 
+%   rate, they shouldn't perform worse.
+%    \begin{macrocode}
+\renewcommand\SpecialIndex[1]{%
+   \expandafter\MakeHarmless \expandafter\@tempa 
+      \expandafter{\string#1}%
+   \IndexEntry{%
+      \LevelSorted{%
+         \expandafter\XD@unbackslash \@tempa\@empty
+      }{\texttt{\@tempa}}%
+   }{none}{\TheXDIndexNumber}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\renewcommand\SpecialMainIndex[1]{%
+   \expandafter\MakeHarmless \expandafter\@tempa 
+      \expandafter{\string#1}%
+   \IndexEntry{%
+      \LevelSorted{%
+         \expandafter\XD@unbackslash \@tempa\@empty
+      }{\texttt{\@tempa}}%
+   }{main}{\TheXDIndexNumber}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\renewcommand\SpecialUsageIndex[1]{%
+   \expandafter\MakeHarmless \expandafter\@tempa 
+      \expandafter{\string#1}%
+   \IndexEntry{%
+      \LevelSorted{%
+         \expandafter\XD@unbackslash \@tempa\@empty
+      }{\texttt{\@tempa}}%
+   }{usage}{\thepage}%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@unbackslash}
+% \begin{macro}{\XD@unbackslash@}
+%   |\XD@unbackslash| is a utility macro which removes the first 
+%   character from a harmless character string if that character is a 
+%   backslash (i.e., if it is |\PrintChar{92}|). The \package{doc} 
+%   commands have traditionally used |\@gobble| for doing this, but the 
+%   \cs{@SpecialIndexHelper@} macro that was comparatively recently added 
+%   tries to do better.
+%    \begin{macrocode}
+\def\XD@unbackslash#1{%
+   \ifx \PrintChar#1%
+      \expandafter\XD@unbackslash@
+   \else
+      \expandafter#1%
+   \fi
+}
+\def\XD@unbackslash@#1{\ifnum #1=92 \else \PrintChar{#1}\fi}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\SpecialMainEnvIndex}
+% \begin{macro}{\SpecialEnvIndex}
+%   These are similar to the above, but \package{doc} thinks that the 
+%   arguments don't need any special care, and it produces two index 
+%   entries per command. |\Special|\-|Env|\-|Index| should  really have 
+%   been called |\Special|\-|Usage|\-|Env|\-|Index|. 
+%    \begin{macrocode}
+\renewcommand\SpecialMainEnvIndex[1]{%
+   \IndexEntry{\LevelSorted{#1}{\texttt{#1} (environment)}}{main}%
+      {\TheXDIndexNumber}%
+   \IndexEntry{\LevelSame{environments:}\LevelSorted{#1}{\texttt{#1}}}%
+      {main}{\TheXDIndexNumber}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\renewcommand\SpecialEnvIndex[1]{%
+   \IndexEntry{\LevelSorted{#1}{\texttt{#1} (environment)}}{usage}%
+      {\thepage}%
+   \IndexEntry{\LevelSame{environments:}\LevelSorted{#1}{\texttt{#1}}}%
+      {usage}{\thepage}%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\it@is@a}
+% \begin{macro}{\XD@special@index}
+%   The |\it@is@a| macro is a specialized version of |\SpecialIndex|, 
+%   but the format of its argument is quite different. After full 
+%   expansion the argument will become a single category 12 token 
+%   (\meta{t}, say), and the control sequence for which an entry should 
+%   be made is |\|\meta{t}. \package{doc} uses |\it@is@a| for control 
+%   sequences with one-character names. Note: The following 
+%   definition should really have special code for the \Module{economical} 
+%   \package{docstrip} module, but I don't think that is necessary 
+%   since the \package{doc} macros which used |\it@is@a| will be
+%   redefined so that they don't.
+%   
+%   |\XD@special@index| does the same thing as |\SpecialIndex|, but it 
+%   does it with \package{xdoc} datatypes---the argument must be a 
+%   harmless character string that does not include the initial escape 
+%   (backslash).
+%   \changes{prot2.1}{2000/11/15}{Using \cs{MakeSortKey} to make the 
+%      sort key. (LH)}
+%    \begin{macrocode}
+\def\it@is@a#1{%
+   \edef\@tempa{#1}%
+   \XD@special@index{\csname XD@harmless@\number
+      \expandafter`\@tempa\endcsname}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\XD@special@index#1{%
+   \MakeSortKey\@tempa{#1}{}%
+   \IndexEntry{\LevelSorted{\@tempa}{\texttt{\Bslash#1}}}{none}%
+      {\TheXDIndexNumber}%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\LeftBraceIndex}
+% \begin{macro}{\RightBraceIndex}
+% \begin{macro}{\PercentIndex}
+% \begin{macro}{\OldMakeIndex}
+%   More specialised forms of |\SpecialIndex|. The |\OldMakeIndex| 
+%   command can safely be made a no-op.
+%    \begin{macrocode}
+\renewcommand\LeftBraceIndex{\XD@special@index{\PrintChar{123}}}
+\renewcommand\RightBraceIndex{\XD@special@index{\PrintChar{125}}}
+\renewcommand\PercentIndex{\XD@special@index{\PrintChar{37}}}
+\let\OldMakeIndex\relax
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\@wrindex}
+%   \changes{prot2.2}{2001/02/13}{Redefinition added. (LH)}
+%   Finally, while we're at redefining indexing commands, let's redefine 
+%   |\@wrindex| as well to ensure that the index entry keyword is the 
+%   same for all indexing commands.
+%    \begin{macrocode}
+\def\@wrindex#1{%
+   \protected@write\@indexfile{}{\XD@index@keyword{#1}{\thepage}}%
+   \endgroup
+   \@esphack
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \section{Cross-referencing}
+% 
+% \subsection{Scanning \texttt{macrocode} for \TeX\ control sequences}
+% \label{Ssec:Scanning macrocode}
+% 
+% The cross-referencing mechanism in \package{doc} isn't problematic in 
+% the same way as the indexing mechanism is, so one could pretty much 
+% leave it as it is, but there are things that are better done 
+% differently when the basic indexing commands are based on harmless 
+% character strings. Rather than storing control sequence names (without 
+% escape character) as sequences of category 11 tokens, they will be 
+% stored as the equivalent harmless character strings.
+% 
+% \begin{macro}{\macro@switch}
+%   As in \package{doc}, |\macro@switch| determines whether the control 
+%   sequence name that follows consists of letters (call |\macro@name|) 
+%   or a single non-letter (call |\short@macro|). Unlike \package{doc}, 
+%   \package{xdoc} accumulates the characters from a multiple-letter 
+%   control sequence name in a token register (|\@toks|), which is why 
+%   that is cleared here.
+%    \begin{macrocode}
+\def\macro@switch{%
+   \ifcat\noexpand\next a%
+      \toks@={}%
+      \expandafter\macro@name
+   \else
+      \expandafter\short@macro
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\scan@macro}
+%   Since |\macro@namepart| isn't used as in \package{doc}, I might as 
+%   well remove the command that cleared it from |\scan@macro|.
+%    \begin{macrocode}
+\def\scan@macro{%
+   \special@escape@char
+   \step@checksum
+   \ifscan@allowed
+      \def\next{\futurelet\next\macro@switch}%
+   \else \let\next\@empty \fi
+   \next}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% 
+% \begin{macro}{\short@macro}
+%   This macro will be invoked (with a single character as parameter)
+%   when a single-character macro name has been spotted whilst
+%   scanning within the \texttt{macrocode} environment. It will produce 
+%   an index entry for that macro, unless that macro has been excluded 
+%   from indexing, and it will also typeset the character that 
+%   constitutes the name of the macro.
+%    \begin{macrocode}
+\def\short@macro#1{%
+   \protected@edef\macro@namepart{%
+%<*economical>
+      \ifnum `#1<\@xxxii
+         \noexpand\PrintChar{\number`#1}%
+      \else\ifnum `#1>126
+         \noexpand\PrintChar{\number`#1}%
+      \else
+%</economical>   
+         \csname XD@harmless@\number`#1\endcsname
+%<economical>      \fi\fi
+   }%
+   \ifnot@excluded \XD@special@index{\macro@namepart}\fi
+%    \end{macrocode}
+%   The cross-referencing mechanism is disabled for when the actual 
+%   character is printed, as it could be the escape character. The index 
+%   entry must be generated before the character is printed to ensure 
+%   that no page break intervenes (recall that a |^^M| will start a new 
+%   line).
+%    \begin{macrocode}
+   \scan@allowedfalse #1\scan@allowedtrue
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% There is one mechanism in |\TeX|'s control sequence tokenization that 
+% |\short@|\B|macro| doesn't cover, and that is the |^^| sequence 
+% substitution---|\^^M| is (with default catcodes) seen as the three 
+% tokens |\^|, |^|, and |M|, not as the single control 
+% sequence token that \TeX\ will make out of it. But this is the way it 
+% is done in \package{doc}.
+% 
+% 
+% \begin{macro}{\macro@name}
+% \begin{macro}{\more@macroname}
+% \begin{macro}{\macro@finish}
+%   Then there's the macros for assembling a control sequence name which 
+%   consists of one or more letters (category 11 tokens). (This includes 
+%   both the characters which are normally letters in the document and 
+%   those that are made letters by |\MakePrivateLetters|.) They're 
+%   pretty straightforward.
+%    \begin{macrocode}
+\def\macro@name#1{%
+%<*economical>
+   \if \ifnum `#1<\@xxxii 1\else \ifnum `#1>126 1\else 0\fi\fi 1%
+      \toks@=\expandafter{\the\expandafter\toks@
+         \expandafter\PrintChar \expandafter{\number`#1}%
+      }%
+   \else
+%</economical>   
+   \toks@=\expandafter{\the\expandafter\expandafter\expandafter\toks@
+      \csname XD@harmless@\number`#1\endcsname}%
+%<economical>   \fi
+   \futurelet\next\more@macroname}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\more@macroname{%
+   \ifcat\noexpand\next a%
+      \expandafter\macro@name
+   \else
+      \macro@finish
+   \fi
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\macro@finish{%
+   \edef\macro@namepart{\the\toks@}%
+   \ifnot@excluded \XD@special@index{\macro@namepart}\fi
+   \macro@namepart
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+%
+%
+%
+% \subsection{The index exclude list}
+% \label{Ssec:Index-exclude}
+% 
+% The index exclude list mechanisms are not quite as simple to convert 
+% for use with harmless character strings as the construction of macro 
+% names are. This is because the trick used for searching the exclude 
+% list for a certain string doesn't work if the string one is looking 
+% for contains tokens with category 1 or 2 (beginning and end of group), 
+% as the \meta{parameter text} of a |\def| cannot contain such tokens. 
+% On the other hand the only groups that can appear in the harmless 
+% character strings one will be looking for are the ones around the 
+% argument of some |\PrintChar|, and these can easily be converted to 
+% something else. Therefore an item in the index exclude list of 
+% \package{xdoc} will have the format
+% \begin{quote}
+%   |\do|\,\meta{string}
+% \end{quote}
+% where the \meta{string} is different from a harmless character string 
+% only in that all |\PrintChar|\marg{num} have been replaced by 
+% |\PrintChar|\parg{num}. The \meta{string} does not include an escape 
+% character. The |\do| serves only to separate the item from the one 
+% before, but it could in principle be used for other purposes as well 
+% (such as in typesetting the entire exclude list).
+% 
+% \begin{macro}{\XD@paren@PrintChar}
+%   |\XD@paren@PrintChar| is a definition of |\PrintChar| which, when it 
+%   is used in an |\edef|, merely replaces the group around the argument 
+%   by a parenthesis and normalizes the number in the argument.
+%   \changes{prot2.1}{2000/09/16}{\cs{number} added. (LH)}
+%    \begin{macrocode}
+\def\XD@paren@PrintChar#1{\noexpand\PrintChar(\number#1)}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\DoNotIndex}
+%   \changes{prot2.1}{2000/09/16}{Also changing catcode of \%. (LH)}
+% \begin{macro}{\do@not@index}
+% \begin{macro}{\XD@do@not@index}
+%   These are the macros which add elements to the index exclude list. 
+%   |\DoNotIndex| is pretty much as in \package{doc}, but I have added 
+%   resetting of the catcodes of `|,|' (since |\XD@do@not@index| relies 
+%   on it) and `|#|' (since it can otherwise mess things up for the 
+%   |\def\@tempa| in |\do@not@index|).
+%    \begin{macrocode}
+\renewcommand\DoNotIndex{%
+   \begingroup
+      \MakePrivateLetters
+      \catcode`\#=12\catcode`\\=12\catcode`,=12\catcode`\%=12
+   \expandafter\endgroup \do@not@index
+}
+%    \end{macrocode}
+%   
+%   |\do@not@index|, on the other hand, is quite different, as it more 
+%   or less has to convert the argument from the format used in 
+%   \package{doc} to that of \package{xdoc}. The bulk of the work is 
+%   done by |\XD@do@not@index|, which grabs one of the elements in the 
+%   argument of |\do@not@index| and converts it (minus the initial 
+%   backslash) to a harmless character string. That harmless character 
+%   string is then converted by |\XD@paren@PrintChar|, so that the 
+%   string can be searched for using |\expanded@notin|.
+%   
+%   The reason for using a special loop structure here, as opposed to 
+%   using for example |\@for|, is that one cannot use either of |\| 
+%   or |,| alone as item separators, as they may both be part of control 
+%   sequence names (consider for example |\DoNotIndex{\a,\\,\b,\,,\c}|), 
+%   but they should be sufficient when combined.
+%   
+%   The reason for storing new elements in |\toks@| until the end of 
+%   the loop and only then inserting them into the index exclude list 
+%   is speed; the index exclude list can get rather large, so you don't 
+%   want to expand it more often than you have to. I don't know if the 
+%   difference is noticeable, though.
+%    \begin{macrocode}
+\begingroup
+   \catcode`\|=0
+   \catcode`\,=12
+   \catcode`\\=12
+%    \end{macrocode}
+%   \SpecialEscapechar{\|}
+%    \begin{macrocode}
+   |gdef|do@not@index#1{%
+      |def|@tempa{#1}%
+      |ifx |@empty|@tempa |else
+         |toks@={}%
+         |expandafter|XD@do@not@index |@gobble #1,\|XD@do@not@index,\%
+      |fi
+   }
+   |gdef|XD@do@not@index#1,\{%
+      |ifx |XD@do@not@index#1%
+         |index@excludelist=|expandafter{%
+            |the|expandafter|index@excludelist |the|toks@
+         }%
+         |expandafter|@gobble
+      |else
+         |MakeHarmless|@tempa{#1}%
+         |begingroup
+            |let|PrintChar|XD@paren@PrintChar
+            |unrestored@protected@xdef|@gtempa{|noexpand|do|@tempa}%
+         |endgroup
+         |toks@=|expandafter{|the|expandafter|toks@ |@gtempa}%
+      |fi
+      |XD@do@not@index
+   }
+|endgroup
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\DoNotIndexHarmless}
+%   The |\DoNotIndexHarmless| command takes a harmless character string 
+%   as argument and locally adds the control sequence whose name is that 
+%   character string to the index exclude list.
+%    \begin{macrocode}
+\newcommand\DoNotIndexHarmless[1]{%
+   \begingroup
+      \let\PrintChar\XD@paren@PrintChar
+      \unrestored@protected@xdef\@gtempa{\noexpand\do#1}%
+   \endgroup
+   \index@excludelist=\expandafter{%
+      \the\expandafter\index@excludelist \@gtempa
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\index@excludelist}
+%   In case the index exclude list is not empty, its contents are 
+%   converted to \package{xdoc} format.
+%    \begin{macrocode}
+\edef\@tempa{\the\index@excludelist}
+\index@excludelist{}
+\ifx \@tempa\@empty \else
+   \def\@tempb#1,\@nil{\do@not@index{#1}}
+   \expandafter\@tempb \@tempa \@nil
+   \let\@tempa\@empty
+   \let\@tempb\@empty
+\fi
+%    \end{macrocode}
+%   The fact that the |\XD@|\B|harmless@|\B\meta{code} table has not 
+%   yet reached its final form means that some of these control sequences 
+%   listed in the exclude list might get a different form here than they 
+%   actually should, but there isn't much that can be done about that. It 
+%   is furthermore unusual that control sequence are given such names 
+%   that they would be affected by this.
+% \end{macro}
+% 
+% \begin{macro}{\ifnot@excluded}
+%   The |\ifnot@excluded| macro ultimately boils down to an 
+%   \texttt{if}, which evaluates to true if and only if the string in 
+%   |\macro@namepart| is not one of the items in the index exclude 
+%   list. Before |\expanded@notin| gets to carry out the actual test, 
+%   the |\PrintChar| calls in |\macro@namepart| are converted by 
+%   |\XD@paren@PrintChar| (it's OK to use an unprotected |\edef| for 
+%   this, since |\PrintChar| is the only control sequence that can 
+%   appear in |\macro@namepart|) so that |\expanded@notin| can be used 
+%   to test for its presence.
+%    \begin{macrocode}
+\def\ifnot@excluded{%
+   \begingroup
+      \let\PrintChar\XD@paren@PrintChar
+      \edef\@tempa{\macro@namepart}%
+   \expandafter\endgroup \expandafter\expanded@notin 
+      \expandafter{\expandafter\do \@tempa\do}%
+      {\the\index@excludelist}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \subsection{External cross-referencing}
+% \label{Ssec:XXR}
+% 
+% (This subsection is a bit speculatory, but I think the structures it 
+% describes may come in handy.)
+% 
+% \changes{prot2}{2000/07/31}{I finally decided that it would be better 
+%    to make the XXR-commands look like comments to \TeX. (LH)}
+% 
+% It's rather easy to write macros for scanning \TeX\ code for the names 
+% of control sequences---just look for the escape (category 0) 
+% character, and whatever follows is the name of a control sequence. 
+% Doing the same thing for other languages may lay anywhere between 
+% ``a~tricky exercise in advanced \TeX\ programming'' and ``possible in 
+% theory'',\footnote{I.e., you know it can be implemented as a computer 
+% program (in some language), you know that any computer program can be 
+% translated to a Turing machine (or if you prefer that, expressed in 
+% lambda calculus), and you know that a Turing machine can be emulated 
+% by \TeX, but that's the closest thing to a solution you've managed to 
+% come up with.} but in most cases the available solutions turn out to be 
+% too complicated and\slash or slow to be of practical use. When that 
+% happens, one might instead want to use some external piece of software 
+% for doing the cross-referencing.
+% 
+% The commands in this subsection implement basic support for such an 
+% external cross-referencing program (or XXR,\footnote{Maybe not the 
+% most logical name, but it looks much cooler than ECR.} for short). The 
+% idea is that an XXR should communicate with \LaTeX\ like \BibTeX\ 
+% does---scan the \texttt{.aux} file (or files, if we're |\include|ing 
+% things) for certain ``commands'' and use them to locate the files to 
+% cross-reference, get parameter settings (like for example entries for 
+% the index exclude list), and so on. It should then cross-reference the 
+% file(s) and write the index entries in a suitable format to some file 
+% (appending them to the \texttt{.idx} file is probably the easiest 
+% solution). This way, it is (almost) as simple to use as the built-in 
+% cross-referencing and the extra work for supporting it is (in 
+% comparison to not supporting it) negligible.
+% 
+% \begin{xrefcmd}{ExternalXRefMsg}
+% \begin{macro}{\SendExternalXRefMsg}
+%   \changes{prot2}{2000/07/28}{Added \cs{if@filesw} test. (LH)}
+%   It's hardly possible to predict all kinds of information that one 
+%   might want to give to an XXR, and neither can one assume that 
+%   there is only one XXR program that will read the \texttt{.aux} 
+%   file. A complicated project might involve code in several languages, 
+%   and each language might have its own XXR. 
+%   Therefore the general XXR-command (text in an \texttt{.aux} file which 
+%   is used for communicating information to an XXR) simply has the syntax
+%   \begin{quote}
+%     \verb*|%%ExternalXRefMsg |\marg{who}\verb*| |\marg{what}
+%   \end{quote}
+%   \meta{who} identifies the XXR this message is meant for. It must be 
+%   balanced text to \TeX\ and may not contain any whitespace, but can 
+%   otherwise be rather arbitrary. \meta{what} is the actual message. It 
+%   too must be balanced text to \TeX\ and it may not contain any 
+%   newlines, but it is otherwise arbitrary. 
+%   \index{whitespace restrictions}^^A
+%   The reason for these restrictions on the contents of \meta{who} and 
+%   \meta{what} is that many (maybe even most) scripting languages 
+%   (which is what at least the \texttt{.aux}-scanning part of an 
+%   XXR will probably be written in) are much better at recognising 
+%   words on a line than they are at recognising a brace-delimited group. 
+%   By accepting these restrictions, one can make sure that all XXRs can 
+%   correctly determine whether a message is for them, even if they see 
+%   the \texttt{.aux} file as a sequence of lines composed of 
+%   whitespace-delimited words.
+%   
+%   |\SendExternalXRefMsg| is the basic command for writing 
+%   |ExternalXRefMsg|s to the \texttt{.aux} file, but it might be 
+%   recommendable that XXR writers provide users with a set of commands 
+%   that have more specific purposes. The syntax of the 
+%   |\Send|\-|External|\-|XRef|\-|Msg| command is (hardly surprising)
+%   \begin{quote}
+%     |\SendExternalXRefMsg|\marg{who}\marg{what}
+%   \end{quote}
+%   |\SendExternalXRefMsg| does a protected full expansion (like 
+%   |\protected@edef|) of its arguments at the time it is called.
+%    \begin{macrocode}
+\newcommand\SendExternalXRefMsg[2]{%
+   \begingroup
+      \if@filesw
+         \let\protect\@unexpandable@protect
+         \immediate\write\@auxout{\@percentchar\@percentchar
+            ExternalXRefMsg {#1} {#2}}%
+      \fi
+   \endgroup
+}
+%    \end{macrocode}
+% \end{macro}\end{xrefcmd}
+% 
+% The remaining commands in this subsection address complications that 
+% exist because of how \texttt{.dtx} files are generally written, and 
+% thus constitutes difficulties that all XXRs will have to face.
+% 
+% \begin{xrefcmd}{ExternalXRefFile}
+%   The usual way to write \texttt{.dtx} files is to include a 
+%   driver---a~short piece of uncommented \LaTeX\ code which contains 
+%   the necessary preamble material and a document body which mainly 
+%   contains a |\DocInput| for the \texttt{.dtx} file itself---but it 
+%   is also usually understood that this driver may be copied to another 
+%   file if necessary and larger projects usually have a completely 
+%   separate driver file. Therefore an XXR cannot be expected to be 
+%   able to find the file(s) to cross-reference simply by changing 
+%   suffix on the name of the \texttt{.aux} file it reads its commands 
+%   from. A more intricate method must be used.
+%   
+%   To tell the XXR that ``here I input the file \dots'', one includes 
+%   an |External|\-|XRef|\-|File| XXR-command in the \texttt{.aux} file. 
+%   Its syntax is
+%   \begin{quote}
+%     \verb*|%%ExternalXRefFile |\marg{cmd}\verb*| |\marg{file}^^A
+%     \verb*| |\marg{what}
+%   \end{quote}
+%   \meta{file} is the name (as given to |\input| or the like) of the 
+%   file to input. \meta{cmd} is either \texttt{begin} (begin of 
+%   \meta{file}) or \texttt{end} (end of \meta{file}). \meta{what} is a 
+%   declaration of what is in the file; XXRs should use it to determine 
+%   whether they should process this file or not. \meta{what} is empty 
+%   if all XXRs should process the file, but for example |\IndexInput| 
+%   will put \texttt{TeX} here to declare that the contents of this file 
+%   are \TeX\ code and only XXRs that cross-reference \TeX\ code need to 
+%   process this file.
+%   
+%   In connection to this, it should be mentioned that XXRs must also look 
+%   for (and act on) |\@input|\penalty\hyphenpenalty\marg{auxfile} commands 
+%   that |\include| or |\DocInclude| has written to the \texttt{.aux} file, 
+%   since these \meta{auxfile}s can also contain commands for the XXR 
+%   that should result in output to the same \texttt{.idx} file. In 
+%   particular, the |ExternalXRefFile| XXR-commands that are written 
+%   because of a |\DocInclude| will be written to such an \meta{auxfile}.
+% \end{xrefcmd}
+% 
+% \begin{xrefcmd}{ExternalXRefSync}
+%   Most XXRs will probably find it an unreasonable task to keep exact 
+%   track of all codelines in all documents, i.e., they will sometimes 
+%   think that a piece of code contains more or fewer numbered 
+%   codelines than it actually does. If for example a document contains 
+%   code such as\iffalse
+%<*example>
+%  \fi
+%\begin{verbatim}
+%% \iffalse
+%%    \begin{macrocode}
+%Etaoin Shrldu
+%%    \end{macrocode}
+%% \fi
+%\end{verbatim}\iffalse
+%</example>
+%\fi
+%   then all reasonable XXRs will probably be fooled into thinking that 
+%   the \texttt{Etaoin Shrldu} line is a numbered codeline. This would 
+%   of course be very bad if an XXR thought it should cross-reference 
+%   the contents of this line, but that shouldn't usually be a problem 
+%   since the specifications\footnote{I imagine these specifications 
+%   will consist of a list of \package{docstrip} options (modules), 
+%   possibly used in combination with restrictions on the names of 
+%   surrounding environments.} of what code should be cross-referenced 
+%   will probably make it clear that the above line should not be 
+%   cross-referenced. Code such as the above will still be problematic 
+%   however, as it will cause the XXR to believe that the 
+%   \texttt{codelineno} counter has another value on any following 
+%   line that is indexed than it actually has in the typeset 
+%   document. This will cause index entries to refer to another line 
+%   than it actually should.
+%   
+%   To overcome this, the |ExternalXRefSync| XXR-command can be used to 
+%   tell the XXR what the corresponding values of |\inputlineno| and 
+%   \texttt{codelineno} are. Its syntax is
+%   \begin{quote}
+%     \verb*|%%ExternalXRefSync |\marg{inputlineno}\verb*| |^^A
+%     \marg{codelineno}
+%   \end{quote}
+%   where \meta{inputlineno} is the expansion of |\the\inputlineno| and 
+%   \meta{codelineno} is the expansion of |\thecodelineno|, both 
+%   expanded at the same point in the program. Note here that the first 
+%   line of a file is line number 1, that line number 0 is used to 
+%   denote ``just before the first line'', and that \texttt{codelineno} 
+%   gets increased immediately before the number is typeset (i.e., 
+%   \texttt{codelineno} contains the number of the last numbered 
+%   codeline).
+% \end{xrefcmd}
+%   
+% This doesn't support external cross-referencing by pages, since doing 
+% that requires that the document outputs a lot more information to the 
+% \texttt{.aux} file. In principle, one could put a |\mark|\penalty0
+% |{\thecodelineno}| in |\PrintCodelineNo| and a |\write| in the page 
+% header which outputs to the \texttt{.aux} file which range of 
+% codelines correspond to a given page, but the \LaTeXe\ sectioning 
+% commands' use of marks tends to interfere with this. The \LaTeXplus\ 
+% package \package{xmarks} will probably solve that problem, though.
+% 
+% \begin{macro}{\syncexternalxref}
+%   \changes{prot2}{2000/07/28}{New name for \cs{SendExternalXRefSync}. 
+%      Also added \cs{if@filesw} test. (LH)}
+%      ^^A Johann Sebastian Bach: 1685/03/21--1750/07/28
+%   The |\syncexternalxref| command writes an |ExternalXRefSync| 
+%   XXR-command for the current line number and value of the 
+%   \texttt{codelineno} counter to \texttt{.aux} file. It is used for 
+%   synchronizing the numbered codeline counter that an XXR maintains with 
+%   the \texttt{codelineno} counter that is used for numbering codelines 
+%   in the typeset document after a piece of code in the document that 
+%   some XXR is likely to misinterpret. |\sync|\-|external|\-|xref| 
+%   shouldn't be used inside \texttt{macrocode} environments (or the 
+%   like) as they tend to read ahead in the file---instead it is best 
+%   placed shortly after such an environment. |\sync|\-|external|\-|xref| 
+%   has no arguments.
+%    \begin{macrocode}
+\newcommand\syncexternalxref{%
+   \if@filesw
+      \immediate\write\@auxout{\@percentchar\@percentchar 
+         ExternalXRefSync {\the\inputlineno} {\thecodelineno}%
+      }%
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{xrefcmd}{ExternalXRefWrap}
+%   The |\DocInclude| command complicates matters for XXRs by redefining 
+%   things so that the \texttt{codelineno} counter only makes up a part 
+%   of the line numbers appearing in the index. The purpose of the 
+%   |External|\-|XRef|\-|Wrap| XXR-command is to inform XXRs about such 
+%   changes. The command
+%   \begin{quote}
+%     \verb*|%%ExternalXRefWrap {|\meta{prefix}\verb*|} {|^^A
+%     \meta{suffix}|}|
+%   \end{quote}
+%   means that codeline numbers written to the index should have the form 
+%   \begin{quote}
+%     \meta{prefix}\meta{codelineno}\meta{suffix}
+%   \end{quote}
+%   This setting takes effect from the next |External|\-|XRef|\-|Sync| 
+%   and stays in effect until the end of the document or until another 
+%   |External|\-|XRef|\-|Wrap| overrides it. The state at the beginning 
+%   of the document is to have both \meta{prefix} and \meta{suffix} 
+%   empty.
+% \end{xrefcmd}
+% 
+% 
+% \begin{macro}{\XD@input}
+%   The |\XD@input| command is a version of |\input| which takes care 
+%   to inform XXRs that another file is being |\input|ted. Its syntax is
+%   \begin{quote}
+%     |\XD@input|\marg{file}\marg{what}
+%   \end{quote}
+%   where \meta{file} is the name of the file to |\input| and \meta{what} 
+%   is the contents of the file, as specified in 
+%   |External|\-|XRef|\-|File| commands.
+%    \begin{macrocode}
+\def\XD@input#1#2{%
+   \if@filesw
+      \immediate\write\@auxout{\@percentchar\@percentchar
+         ExternalXRefFile {begin} {#1} {#2}%
+      }%
+      \immediate\write\@auxout{\@percentchar\@percentchar
+         ExternalXRefSync {0} {\thecodelineno}%
+      }%
+   \fi
+   \input{#1}%
+   \if@filesw
+      \immediate\write\@auxout{\@percentchar\@percentchar
+         ExternalXRefFile {end} {#1} {#2}%
+      }%
+      \immediate\write\@auxout{\@percentchar\@percentchar
+         ExternalXRefSync {\the\inputlineno} {\thecodelineno}%
+      }%
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\DocInput}
+%   The |\DocInput| command is redefined so that it writes 
+%   |External|\-|XRef|\-|File| and |External|\-|XRef|\-|Sync| XXR-commands 
+%   to the \texttt{.aux} file. Furthermore, with \package{xdoc} one 
+%   should always use the |\DocInput| command (or some command based on 
+%   it, like |\DocInclude|) for inputting a file where percent is an 
+%   `ignore' character---even when one such file inputs another. (Doing 
+%   that didn't work with the \package{doc} definition, as it always 
+%   called |\MakePercentComment| upon return, but the \package{xdoc} 
+%   definition contains code for dealing with that.)
+%    \begin{macrocode}
+\renewcommand\DocInput[1]{%
+   \relax
+   \ifnum \catcode`\%=14
+      \expandafter\@firstoftwo
+   \else
+      \expandafter\@secondoftwo
+   \fi{%
+      \MakePercentIgnore\XD@input{#1}{}\MakePercentComment
+   }{\XD@input{#1}{}}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\IndexInput}
+%   The |\IndexInput| command also needs to be redefined to write 
+%   XXR-commands to the \texttt{.aux} file. It would 
+%   probably be enough here to write an |External|\-|XRef|\-|Sync| 
+%   after the file has been |\input| since no external 
+%   cross-referencing of |\IndexInput|ted files is needed, but I do the 
+%   more verbose variant here just to exemplify how these things would 
+%   look for other languages.
+%    \begin{macrocode}
+\renewcommand\IndexInput[1]{%
+   \begingroup
+      \macro@code
+      \frenchspacing
+      \@vobeyspaces
+      \XD@input{#1}{TeX}%
+      \endmacrocode
+   \endgroup
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% 
+% \section{Two-sided printing}
+% \label{Sec:Twoside}
+% 
+% The main problem one faces when reimplementing \package{doc} so that 
+% the marginal material always appears in the outer margin in two-sided 
+% documents is that the justification of \package{doc}'s marginal 
+% material is asymmetric; it always extends outwards. This means that 
+% the justification to use when typesetting the marginal material must 
+% depend on whether it is to be put on a left or a right 
+% page---something which cannot be determined for sure when the 
+% material is typeset! This is a minor difficulty if the marginal material 
+% is put in place using \LaTeX's |\marginpar| command, as that allows the 
+% user to supply different versions of the marginal paragraph for left and 
+% right margin placements. It is however a major difficulty if the 
+% marginal material is displaced out into the margin from within the main 
+% galley (like the \texttt{macro} environment of \package{doc} does), 
+% since the output routine is never involved.
+% 
+% Even though this difficulty provides arguments for using a |\marginpar| 
+% mechanism for all text that is put in the margin, that will not be 
+% done in \package{xdoc} (but maybe it will in some successor). 
+% Instead \package{xdoc} contains a general mechanism which uses data 
+% written to the \texttt{.aux} file for determining whether a piece of 
+% text was put on an odd or even numbered page the \emph{last} time the 
+% document was typeset. By the usual convergence of page breaks in a 
+% \LaTeX\ document, this will eventually produce a typeset document 
+% with the marginal material consistently in the outer margin.
+% 
+% The mechanism works as follows. The places in the document (the 
+% document source) at which it is necessary to determine whether 
+% something is going to appear on an even (left) or an odd (right) page 
+% are called ``page situations''\footnote{I know it's not a particularly 
+% good name. Suggestions for better names are gracefully accepted.} or 
+% just ``situations''. In each situation, a relatively simple test (is 
+% the \texttt{page} counter currently even or odd?) which is right more 
+% often than not is used as a first guess, and both the guess, the 
+% placement actually used, and the correct answer (determined from the 
+% value of \texttt{page} when the piece of text is shipped out) are 
+% recorded in the \texttt{.aux} file. If the guess (for the current 
+% situation) coincided with the correct answer the last time the 
+% document was typeset then the guess determined now is used, otherwise 
+% the opposite of the guess determined now is used. Finally, when at 
+% |\end{document}| the \texttt{.aux} file is inputted to check for 
+% changed labels, the placements used are also checked and the user is 
+% given a suitable warning if there was an incorrect one.
+% 
+% \begin{macro}{\IfOddPageSituation}
+%   The |\IfOddPageSituation| macro is the user level test for whether 
+%   the current page situation appears on an odd or an even page. It 
+%   has the syntax
+%   \begin{quote}
+%     |\IfOddPageSituation|\marg{odd}\marg{even}
+%   \end{quote}
+%   and this will expand to \meta{odd} if the current situation is 
+%   expected to end up on an odd page (based on how correct it was to 
+%   look at the value of \texttt{page} last time) and to \meta{even} 
+%   otherwise. In single-sided mode, it always expands to \meta{even}. 
+%   In two-sided mode, |\IfOddPageSituation| is redefined for the new 
+%   situation each time |\StepPageSituation| is called.
+%    \begin{macrocode}
+\let\IfOddPageSituation=\@secondoftwo
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\StepPageSituation}
+%   \changes{prot2.1}{2000/12/19}{Now also setting 
+%      \cs{IfOddPageSituation}, instead of having that macro performing 
+%      the test each time it is used. This fixes a rarely occuring bug 
+%      which occurs when a page is shipped out between 
+%      \cs{StepPageSituation} and a corresponding 
+%      \cs{IfOddPageSituation}. (LH)}
+% \begin{macro}{\macro@cnt}
+% \begin{macro}{\XD@next@wrong}
+% \begin{macro}{\XD@wrongs@list}
+%   The |\StepPageSituation| command is called to inform the page 
+%   situation mechanism that a new situation has begun. The rule for 
+%   when you need to use |\Step|\-|Page|\-|Situation| is simple: if you 
+%   use |\IfOdd|\-|Page|\-|Situation| in two places which may end up on 
+%   different pages, then there must be a |\Step|\-|Page|\-|Situation| 
+%   between them. There is no code which automatically calls 
+%   |\Step|\-|Page|\-|Situation|---not even |\clearpage| or other 
+%   macros which force page breaks do this---hence macros which use 
+%   the page situation mechanism must always call |\Step|\-|Page|\-^^A
+%   |Situation| explicitly when a new situation begins.
+% 
+%   Since the |\macro@cnt| count register isn't used for stacking 
+%   marginal headings (``macro'' names) anymore (see below), it is 
+%   employed for enumerating page situation. |\XD@next@wrong| is a macro 
+%   which contains the number of the next situation in which the guess 
+%   was wrong last time. Unless |\XD@next@wrong|${}={}$|\macro@cnt|, the 
+%   guess was right last time. All assignments to |\macro@cnt| and
+%   |\XD@next@wrong| are global.
+%   
+%   |\XD@wrongs@list| is a list of all the wrong guesses. It has the 
+%   syntax
+%   \begin{quote}
+%     |\@elt|\marg{guess no.}|\@elt|\marg{guess no.}\dots
+%     |\@elt|\marg{guess no.}
+%   \end{quote}
+%   where the \meta{guess no.}s are the numbers of the wrong guesses, in 
+%   increasing order. The contents of |\XD@wrongs@list| are collected 
+%   when the \texttt{.aux} file is inputted at |\begin|\B|{document}|, 
+%   and they are removed again as \TeX\ passes the situation in the 
+%   document that they apply to. All assignments to |\XD@wrong@list| are 
+%   global.
+%   
+%   Calling |\StepPageSituation| increases |\macro@cnt| by one, 
+%   updates |\XD@|\B|next@|\B|wrong| and |\XD@|\B|wrong@|\B|list| 
+%   appropriately, and sets |\IfOdd|\B|Page|\B|Situation| to 
+%   |\@firstoftwo| or |\@secondoftwo| (whichever is correct for this 
+%   situation). |\@next| is a list management macro from the \LaTeX\ 
+%   kernel.
+%    \begin{macrocode}
+\if@twoside
+   \def\StepPageSituation{%
+      \global\advance \macro@cnt \@ne
+      \ifnum \XD@next@wrong<\macro@cnt
+         \global\@next\XD@next@wrong\XD@wrongs@list{}{%
+            \let\XD@next@wrong\maxdimen
+         }%
+      \fi
+      \ifnum \ifodd\c@page -\fi \@ne=%
+         \ifnum \XD@next@wrong=\macro@cnt -\fi \@ne
+         \global\let\IfOddPageSituation\@secondoftwo
+      \else
+         \global\let\IfOddPageSituation\@firstoftwo
+      \fi
+   }
+   \def\XD@next@wrong{-\maxdimen}
+   \let\XD@wrongs@list\@empty
+\else
+   \let\StepPageSituation=\relax
+\fi
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}\end{macro}
+% 
+% 
+% \begin{macro}{\RecordPageSituation}
+%   The |\RecordPageSituation| command generates a |\write| whatsit node 
+%   which records the outcome of the current page situation. It is the 
+%   location of this whatsit node that determines on which page a 
+%   certain situation is considered to occur. If you don't execute this 
+%   macro for a certain page situation, the first guess will always be 
+%   used for that situation and no warnings will be given if that guess 
+%   is incorrect. In single-sided mode, this is a no-op (thus you should 
+%   better place it somewhere where it doesn't affect spacing). 
+%   Furthermore you must make sure that \TeX\ does not change the value 
+%   of the \texttt{page} counter between a |\StepPageSituation| and its 
+%   corresponding |\RecordPageSituation|, since the |\ifodd| test must 
+%   yield the same result in both cases.
+%   
+%    \begin{macrocode}
+\if@twoside
+   \def\RecordPageSituation{%
+      \if@filesw
+         \edef\@tempa{%
+            \string\XD@situation{\the\macro@cnt}{%
+               \ifodd\c@page 1\else 0\fi
+            }{\IfOddPageSituation{1}{0}}%
+         }%
+         \write\@auxout\expandafter{\@tempa{\ifodd\c@page 1\else 0\fi}}%
+      \fi
+   }%
+\else
+   \let\RecordPageSituation=\relax
+\fi
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \begin{macro}{\XD@situation}
+%   \changes{prot2}{2000/07/13}{Changed to allow multiple 
+%     \cs{XD@situation} commands for the same situation. This is 
+%     necessary for coping with documents which \cs{include} files. (LH)}
+%   \changes{prot2}{2000/07/26}{Made redefinition at begin document 
+%      global. (LH)}
+% \begin{macro}{\XD@check@situation}
+%   |\XD@situation| is the command that will be written to the 
+%   \texttt{.aux} file with the data about how the situation turned out. 
+%   Its syntax is
+%   \begin{quote}
+%     |\XD@situation|\marg{number}\marg{guess}\marg{did}\marg{correct}
+%   \end{quote}
+%   where \meta{number} is the number of the situation, and 
+%   \meta{guess}, \meta{did}, and \meta{correct} describe what the 
+%   guess, the actual action done, and what the correct action to do 
+%   respectively was. \meta{guess}, \meta{did}, and \meta{correct} are 
+%   either |0| (denoting even page) or |1| (denoting odd page).
+%   
+%   The definition for |\XD@situation| set here is the one which will 
+%   be in force when the \texttt{.aux} file is inputted at |\begin|\B
+%   |{document}|; its purpose is to build the |\XD@wrongs@list|. 
+%   |\XD@check@situation| is the definition for |\XD@situation| which 
+%   will be in force when the \texttt{.aux} file is inputted at 
+%   |\end|\B|{document}|; its purpose is to check if anything was 
+%   incorrectly placed.
+%   
+%   The main problem |\XD@situation| has to face is that text in the 
+%   \texttt{.dvi} file needs not appear in exactly the same order as it 
+%   was typeset, and it is therefore possible that |\XD@situation|s in 
+%   the \texttt{.aux} file do not appear in increasing \meta{number} 
+%   order. Because of this, |\XD@situation| must sort the 
+%   |\XD@wrongs@list| while constructing it. The only reasonable 
+%   algorithm for this seems to be insertion sort, but as the items to 
+%   insert are almost surely almost sorted, a special check is done in 
+%   the beginning to see if that is the case. |\XD@next@wrong| is used 
+%   in this to store the number of the last item so far inserted into 
+%   the |\XD@wrongs@list|. By only assigning |\XD@next@wrong| locally 
+%   here, one is relieved of having to reset it in |\AtBeginDocument| 
+%   code.
+%   
+%   When sorting is actually applied, a new item |\@elt|\marg{insert} 
+%   is inserted through expanding the list. When doing that, the |\@elt| 
+%   macro has the syntax
+%   \begin{quote}
+%     |\@elt|\,\meta{flag}\,\marg{number}\,\meta{next}
+%   \end{quote}
+%   where \meta{flag} is |\BooleanTrue| or |\BooleanFalse|, \meta{number} 
+%   is the item that the |\@elt| belong to, and \meta{next} is either the 
+%   next |\@elt| or |\@gobble| (if this is the last). The \meta{flag} 
+%   specifies whether the item has been inserted; |\Boolean|\B|True| means 
+%   that it has. The above |\@elt|-sequence will expand to
+%   \begin{quote}
+%     |\noexpand|\,|\@elt|\,\marg{number}\,\meta{next}\,|\BooleanTrue|
+%   \end{quote}
+%   if \meta{flag} is |\BooleanTrue|, or \meta{flag} is |\BooleanFalse| 
+%   and \meta{number} is equal to \meta{insert}. It will expand to
+%   \begin{quote}
+%     |\noexpand|\,|\@elt|\,\marg{number}\,\meta{next}\,|\BooleanFalse|
+%   \end{quote}
+%   if \meta{flag} is |\BooleanFalse| and \meta{number} is less than 
+%   \meta{insert}. It expands to
+%   \begin{quote}
+%     |\noexpand|\,|\@elt|\,\marg{insert}\,|\noexpand|\,|\@elt|^^A
+%       \,\marg{number}\\
+%     \meta{next}\,|\BooleanTrue|
+%   \end{quote}
+%   if \meta{flag} is |\BooleanFalse| and \meta{number} is greater than 
+%   \meta{insert}.
+%   
+%    \begin{macrocode}
+\if@twoside
+   \def\XD@situation#1#2#3#4{%
+      \if #2#4\else
+         \ifnum #1<\XD@next@wrong
+            \begingroup
+               \def\@elt##1##2##3{%
+                  \noexpand\@elt
+                  \ifcase
+                     \ifx ##1\BooleanTrue 0%
+                     \else\ifnum ##2<#1 1%
+                     \else\ifnum ##2>#1 2%
+                     \else 0%
+                     \fi\fi\fi
+                  \space
+                     {##2}\expandafter\@secondoftwo
+                  \or
+                     {##2}\expandafter\@firstoftwo
+                  \else
+                     {#1}\noexpand\@elt{##2}\expandafter\@secondoftwo
+                  \fi{##3\BooleanFalse}{##3\BooleanTrue}%
+               }%
+               \xdef\XD@wrongs@list{%
+                  \expandafter\expandafter \expandafter\@elt 
+                  \expandafter\@firstoftwo \expandafter\BooleanFalse
+                  \XD@wrongs@list \@gobble
+               }%
+            \endgroup
+         \else\ifnum #1>\XD@next@wrong
+            \def\XD@next@wrong{#1}%
+            \expandafter\gdef \expandafter\XD@wrongs@list
+               \expandafter{\XD@wrongs@list \@elt{#1}}%
+         \fi\fi
+      \fi
+   }
+   \def\XD@check@situation#1#2#3#4{%
+      \if #3#4\else
+         \PackageWarningNoLine{xdoc2}{Page breaks may have changed.%
+            \MessageBreak Rerun to get marginal material right}%
+         \let\XD@situation\@gobblefour
+      \fi
+   }
+   \AtBeginDocument{\global\let\XD@situation\XD@check@situation}
+\else
+   \let\XD@situation\@gobblefour
+\fi
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% 
+% \begin{macro}{\XD@set@situation}
+% \begin{macro}{\XD@write@situation@ckpt}
+% \begin{macro}{\cl@@ckpt}
+%   The page situation counter |\macro@cnt| is closely related to the 
+%   \texttt{page} counter and it needs to be among the counters whose 
+%   values are recorded in |\include| checkpoints, since the enumeration 
+%   of situations will otherwise change when files are added to or 
+%   removed from the |\@partlist|. It is not sufficient to simply set 
+%   the value of |\macro@cnt| however; one must also advance to the 
+%   correct position in the |\XD@wrongs@list| list and set 
+%   |\XD@next@wrong| accordingly. The |\XD@set@situation| command has 
+%   the syntax
+%   \begin{quote}
+%     |\XD@set@situation|\marg{number}
+%   \end{quote}
+%   It sets |\macro@cnt| to \meta{number} and updates |\XD@wrongs@list| 
+%   and |\XD@|\B|next@|\B|wrong| accordingly.
+%    \begin{macrocode}
+\if@twoside
+   \def\XD@set@situation#1{%
+      \global\macro@cnt=#1\relax
+      \loop \ifnum \XD@next@wrong<\macro@cnt
+         \global\@next\XD@next@wrong\XD@wrongs@list{}{%
+            \let\XD@next@wrong\maxdimen
+         }%
+      \repeat
+   }
+\else \let\XD@set@situation=\@gobble \fi
+%    \end{macrocode}
+%   
+%   The |\XD@write@situation@ckpt| macro writes an |\XD@set@situation| 
+%   command to the \texttt{.aux} file in the way that |\@wckptelt| 
+%   writes |\setcounter| commands for normal counters. A problem for 
+%   |\XD@write@situation@ckpt| is that it will have to appear in a 
+%   macro which is regularly subjected to the |\xdef| in |\@cons|. For 
+%   that reason, it will simply expand to itself whenever |\@elt| isn't 
+%   |\@wckptelt|.
+%    \begin{macrocode}
+\if@twoside
+   \def\XD@write@situation@ckpt{%
+      \ifx \@elt\@wckptelt
+         \immediate\write\@partaux{%
+            \string\XD@set@situation{\the\macro@cnt}%
+         }%
+      \else
+         \noexpand\XD@write@situation@ckpt
+      \fi
+   }
+   \expandafter\def \expandafter\cl@@ckpt
+      \expandafter{\cl@@ckpt \XD@write@situation@ckpt}
+\fi
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% 
+% 
+% \section{The list of changes}
+% \label{Sec:Changes}
+% 
+% Reimplementations elsewhere have required a few modifications related 
+% to the |\changes| command. There are a lot of other things that could 
+% and perhaps should be done with these mechanisms, though.
+% 
+% \begin{macro}{\saved@macroname}
+%   The contents of the |\saved@macroname| macro now have the syntax
+%   \begin{quote}
+%     \marg{sort key}\marg{text}
+%   \end{quote}
+%   i.e., exactly like the argument sequence of |\LevelSorted|. It's not 
+%   fed to that macro right now, but it is not unlikely that it will in 
+%   the future. The default definition corresponds to the default 
+%   definition in \package{doc}.
+%    \begin{macrocode}
+\def\saved@macroname{{ }{\generalname}}
+%    \end{macrocode}
+%   Unlike the case in \package{doc}, the formatting of the text in 
+%   |\saved@macroname| must be included.
+% \end{macro}
+% 
+% \begin{macro}{\if@version@key@}
+%   The |@version@key@| switch is used for supporting intelligent 
+%   sorting of version numbers. It is normally false, but at times 
+%   where the version number argument of |\changes| is being expanded 
+%   because it will be used as a sort key then it is true. This is used 
+%   by the |\uintver| macro. Assignments to this switch are as a rule 
+%   global, since it is never true for any longer time.
+%   \changes{prot2.4}{2002/11/01}{Switch added. (LH)}
+%    \begin{macrocode}
+\newif\if@version@key@
+\@version@key@false
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\uintver}
+%   The |\uintver| command can be used in the \meta{version} argument 
+%   of |\changes| to ensure that (unsigned) integers are sorted in 
+%   mathematical rather than ASCII order by \package{makeindex}. Thus 
+%   if for example version |1.10| is later than version |1.9| then one 
+%   should write this as
+%   \begin{quote}
+%     |\changes{1.\uintver{10}}{|\dots
+%   \end{quote}
+%   The general syntax is
+%   \begin{quote}
+%     |\uintver|\marg{number}
+%   \end{quote}
+%   and this expands completely in \TeX's mouth.
+%   \changes{prot2.4}{2002/11/01}{Command added. (LH)}
+%   
+%   The idea is that 0--9 are compared as 0--9, whereas 10--99 are 
+%   compared as A10--A99, 100--999 are compared as B100-B999, and so on. 
+%   The comparisons are correct up to 99999, but it could easily be 
+%   extended further.
+%    \begin{macrocode}
+\newcommand*\uintver[1]{%
+   \if@version@key@
+      \ifnum #1>9
+         \ifnum #1<100
+            A%
+         \else\ifnum #1<\@m
+            B%
+         \else\ifnum #1<\@M
+            C%
+         \else
+            D%
+         \fi\fi\fi
+      \fi
+   \fi
+   \expandafter\@firstofone \expandafter{\number#1}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+%   
+% \begin{macro}{\changes@}
+%   This |\changes@| is a simple redefinition of the \package{doc} 
+%   macro with the same name. The main difference is that all 
+%   formatting of the second entry level has been taken out---it is 
+%   supposed to be provided in |\saved@macroname|---but in addition to 
+%   that the date is being used as a third level sort key and |\uintver| 
+%   may be used in the version number to correct the data.
+%   \changes{prot2.4}{2002/11/01}{Added support for \cs{uintver}. (LH)}
+%   
+%   The former makes more sense for projects where the date is 
+%   increased faster than the version number and it doesn't change 
+%   anything relevant in the remaining cases. The latter is necessary 
+%   if version numbers are assigned for example by CVS.
+%    \begin{macrocode}
+\def\changes@#1#2#3{%
+   \global\@version@key@true
+   \protected@edef\@tempa{#1}%
+   \global\@version@key@false
+   \protected@edef\@tempa{%
+      \noexpand\glossary{%
+         \@tempa\actualchar#1\levelchar
+         \expandafter\@firstoftwo\saved@macroname\actualchar
+            \expandafter\@secondoftwo\saved@macroname:\levelchar
+         #2\actualchar#3%
+      }%
+   }%
+   \@tempa
+   \endgroup
+   \@esphack
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\@wrglossary}
+%   \changes{prot2.2}{2001/02/13}{Redefinition added. (LH)}
+% \begin{macro}{\XD@glossary@keyword}
+%   \changes{prot2.2}{2001/02/13}{Macro added. (LH)}
+%   The |\@wrglossary| macro is the one which actually writes entries 
+%   to the \texttt{.glo} file. It is redefined by \package{xdoc} to put 
+%   the contents of |\XD@glossary@keyword|, rather than a hardwired 
+%   |\glossaryentry|, in front of the glossary entry. 
+%   |\XD@glossary@keyword| is redefined by the \package{docindex} 
+%   package~\cite{docindex}.
+%    \begin{macrocode}
+\def\@wrglossary#1{%
+   \protected@write\@glossaryfile{}%
+      {\XD@glossary@keyword{#1}{\thepage}}%
+   \endgroup
+   \@esphack
+}
+\@ifundefined{XD@glossary@keyword}{%
+   \edef\XD@glossary@keyword{\@backslashchar glossaryentry}%
+}{}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\definechange}
+% \begin{macro}{\XD@definechange}
+%   The |\definechange| command has the syntax
+%   \begin{quote}
+%     |\definechange|\marg{name}\marg{version}\marg{date}\marg{text}
+%   \end{quote}
+%   The three last arguments are precisely like the arguments of 
+%   |\changes|, but |\definechange| doesn't write the change to the 
+%   \texttt{.glo} file; instead it stores them away as the ``named 
+%   change'' \meta{name}, for later use in the |\usechange| command.
+%    \begin{macrocode}
+\newcommand\definechange{%
+   \begingroup\@sanitize
+   \catcode`\\\z@ \catcode`\ 10 \MakePercentIgnore
+   \expandafter\endgroup \XD@definechange
+}
+\def\XD@definechange#1#2#3#4{\@namedef{XD@ch-#1}{{#2}{#3}{#4}}}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% The named changes are stored in the 
+% \describecsfamily{XD@ch-\meta{name}}|\XD@ch-|\meta{name} family of 
+% control sequences. These are parameterless macros with replacement 
+% texts of the form
+% \begin{quote}
+%   \marg{version}\marg{date}\marg{text}
+% \end{quote}
+% 
+% \begin{macro}{\usechange}
+% \begin{macro}{\XD@usechange}
+%   \changes{prot2.4}{2002/11/01}{Added support for \cs{uintver}. (LH)}
+%   To use a named change defined earlier, one of course uses the 
+%   command |\usechange|, which has the syntax
+%   \begin{quote}
+%     |\usechange|\marg{name}
+%   \end{quote}
+%   The effect of this is similar to that of a general |\changes| 
+%   (i.e., it appears outside all \texttt{macro}-like environments) with 
+%   the arguments specified in the |\definechange|, but this also 
+%   includes the macro (or whatever) name with the page number, using 
+%   the encapsulation mechanism in \package{makeindex}.
+%    \begin{macrocode}
+\newcommand*\usechange[1]{%
+   \@ifundefined{XD@ch-#1}{%
+      \PackageError{xdoc2}{Named change `#1' undefined}\@eha
+   }{%
+      \expandafter\expandafter \expandafter\XD@usechange
+         \csname XD@ch-#1\endcsname
+   }%
+}
+\def\XD@usechange#1#2#3{%
+   \def\@tempa{{ }{\generalname}}%
+   \ifx \@tempa\saved@macroname
+      \let\@tempa\@empty
+   \else
+      \protected@edef\@tempa{%
+         \encapchar labelednumber%
+         {\expandafter\@secondoftwo\saved@macroname}%
+      }
+   \fi
+   \global\@version@key@true
+   \protected@edef\@tempb{#1}%
+   \global\@version@key@false
+   \glossary{%
+      \@tempb\actualchar #1\levelchar
+      \space\actualchar\generalname:\levelchar
+      #2\actualchar#3\@tempa
+   }%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\labelednumber}
+%   The |\labelednumber| macro belongs to the same category as the 
+%   |\main| and |\usage| macros, but it takes an extra argument. The 
+%   syntax is
+%   \begin{quote}
+%     |\labelednumber|\marg{extra}\marg{number}
+%   \end{quote}
+%   which typesets as
+%   \begin{quote}
+%     \meta{number} (\meta{extra})
+%   \end{quote}
+%    \begin{macrocode}
+\newcommand*\labelednumber[2]{#2\nolinebreak[2] (#1)}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% 
+% \section{\texttt{macro}-like environments}
+% \label{Sec:Macro-environments}
+% 
+% There are several reasons one might want to improve the \texttt{macro} 
+% and \texttt{environment} environments.
+% \begin{itemize}
+%   \item
+%     The code in them cannot be reused if you want to define other 
+%     things than \TeX\ macros or \LaTeX\ environments. (During the 
+%     last year or so, I have defined \texttt{macro}-like environments 
+%     for over a dozen different things.)
+%   \item
+%     They always put the macro\slash environment name to the left of 
+%     the current column. This is inappropriate for two-sided printing, 
+%     as there should be a symmetry over an entire spread in that case.
+%   \item
+%     The vertical extent of a macro\slash environment name must not 
+%     exceed that of the |\strut|, since they will otherwise overprint 
+%     each other when stacked. In particular this makes it impossible to 
+%     make line breaks in macro names---something which would otherwise 
+%     be of interest in projects (such as for example \cite{fontinst}) 
+%     where some names are very long and obvious breakpoints are 
+%     available.
+% \end{itemize}
+% (I'm quite sure there are more things that have annoyed me, but I can't 
+% remember which they are right now.) The redefinitions below take care 
+% of the all these problems.
+% 
+% 
+% \subsection{Grabbing arguments}
+% 
+% A special feature of the \texttt{macro}-like environments is that (at 
+% least some) of their arguments must be given rather special treatment. 
+% This special treatment usually consists of making temporary |\catcode| 
+% changes for the time these arguments are tokenized---since the standard 
+% |\catcode|s for some important characters tend to be unsatisfactory in 
+% these cases---but there are other possibilities as well. For that 
+% reason, the \package{xdoc} package employs a mechanism that is very 
+% similar to that used in the Mittelbach--Rowley--Carlisle 
+% \package{xparse} package~\cite{xparse}, although it does not share 
+% any code with that. I call this mechanism the argument grabber.
+% 
+% The heart of the argument grabber is the macro |\XD@grab@arguments|, 
+% which has the following syntax:
+% \begin{quote}
+%   |\XD@grab@arguments|\marg{call}\marg{grabber sequence}^^A
+%      \meta{arguments to grab}
+% \end{quote}
+% \meta{call} is something which will eventually be placed in front of 
+% all the arguments grabbed. It can simply be a single macro, but it 
+% can also contain some arguments for that macro. \meta{grabber sequence} 
+% is a sequence of grabbers. A \emph{grabber} is typically a macro which 
+% grabs the next argument and stores it in a token list together with the 
+% arguments that were grabbed before. A grabber could however be some 
+% more complex piece of code that performs a similar action.
+% 
+% \begin{table}
+%   \begin{minipage}{\columnwidth}
+%     \begin{center}\small
+%     \begin{tabular}{lll>{\raggedright}p{0.3\linewidth}}
+%       \textbf{Grabber}& \textbf{Arg.\ type}& 
+%         \textbf{Catcodes\footnote[1]{Catcode settings key: 
+%         --- = no change, PL = changes made by \cs{MakePrivateLetters}, 
+%         OB = set the catcode of backslash to ordinary.}}&
+%         \textbf{Post-processing}\tabularnewline
+%       |\XD@grab@marg|& Mandatory& ---& None\tabularnewline
+%       |\XD@grab@oarg|& Optional& ---& None\tabularnewline
+%       |\XD@grab@sarg|\marg{char}& 1-char optional&
+%         ---& Returns |\BooleanTrue| if the character was present 
+%         and |\BooleanFalse| otherwise.\tabularnewline
+%       |\XD@grab@withprivate|& Mandatory& PL& None\tabularnewline
+%       |\XD@grab@asmacro|\footnote[2]{This grabber is probably obsolete; 
+%         it is included because it grabs the argument in precisely the 
+%         way that the \texttt{macro} environment of \package{doc} does.}& 
+%         Mandatory& OB+PL& None\tabularnewline
+%       |\XD@grab@harmless|\meta{proc}& Mandatory& ---& 
+%         |\MakeHarmless| followed by \meta{proc}\tabularnewline
+%       |\XD@grab@harmless@oarg|& Optional& ---& 
+%         |\MakeHarmless|\tabularnewline
+%       \multicolumn{3}{l}{\cs{XD@grab@harmless@asmacro}}\tabularnewline
+%       & Mandatory& OB+PL& 
+%         |\MakeHarmless| followed by |\XD@unbackslash|\tabularnewline
+%       |\XD@grab@harmless@cs|& Mandatory\footnote[3]{The argument is 
+%         normally precisely one control sequence.}& PL& 
+%         |\string| whilst |\escapechar| is set to \textminus1, 
+%         followed by |\MakeHarmless|\tabularnewline
+%       \multicolumn{3}{l}{^^A
+%         \cs{XD@grab@harmless@withprivate}\marg{proc}}\\
+%       & Mandatory& PL& |\MakeHarmless| followed by \meta{proc}
+%     \end{tabular}
+%     \end{center}
+%   \end{minipage}
+%     
+%   \caption{Grabbers currently defined by \package{xdoc}}
+%   \label{Tab:Grabbers}
+% \end{table}
+% 
+% When arguments are being grabbed, the \meta{call} is stored in |\toks@| 
+% and the arguments are appended to |\toks@| as they are grabbed. For 
+% that reason, a grabber may not itself call |\XD@grab@arguments|, nor 
+% may it use a command defined through \package{xparse}'s 
+% |\Declare|\-|Document|\-|Command| or anything else which uses this 
+% token register in a bad way.
+% 
+% When a grabber is expanded, it is in the context
+% \begin{quote}
+%   \meta{grabber}\,\meta{following grabbers}\,|\XD@endgrab|\penalty0
+%   \thinspace\meta{ungrabbed arguments}
+% \end{quote}
+% After it has grabbed its argument, everything of the above should be 
+% put back except for the \meta{grabber} and the argument it grabbed. 
+% The argument itself should be wrapped in a group and appended to 
+% |\toks@|.
+% 
+% \textbf{Note:} In prototype~2 the format in which the argument grabber 
+% returns the grabbed arguments was changed so that it can now be 
+% unified with argument grabbing mechanisms of \package{xparse}. I 
+% think this should be done some time in the future, but for the moment 
+% it seems best not to rely on \LaTeXplus\ packages like \package{xparse}.
+% 
+% \begin{macro}{\XD@grab@arguments}
+% \begin{macro}{\XD@endgrab}
+%   \changes{prot2}{2000/07/13}{The grabbed arguments are no longer 
+%      returned wrapped up in a group. There is no longer a need for 
+%      storing the base call separately in \cs{toks}\,\texttt{2}. (LH)}
+%   The |\XD@grab@arguments| and |\XD@endgrab| macros set up and finish 
+%   off argument grabbing.
+%    \begin{macrocode}
+\def\XD@grab@arguments#1#2{%
+   \toks@={#1}%
+   #2\XD@endgrab
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\def\XD@endgrab{\the\toks@}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@grab@marg}
+%   A grabber for ordinary arguments, like the \texttt{m} arguments of 
+%   \package{xparse}.
+%    \begin{macrocode}
+\long\def\XD@grab@marg#1\XD@endgrab#2{%
+   \addto@hook\toks@{{#2}}%
+   #1\XD@endgrab
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\XD@grab@oarg}
+% \begin{macro}{\XD@grab@oarg@}
+%   A grabber for optional arguments (\texttt{o} arguments in 
+%   \package{xparse}). It looks ahead for an optional argument and 
+%   grabs that argument if there was one. If it doesn't find anything 
+%   which looks like an optional argument (i.e., if the next character 
+%   isn't a |[|), then the grabber will not grab anything (although it 
+%   may have tokenized the next argument), but it will still append 
+%   |\NoValue| to |\toks@|.
+%   
+%    \begin{macrocode}
+\def\XD@grab@oarg#1\XD@endgrab{%
+   \@ifnextchar[{\XD@grab@oarg@{#1}}{%
+      \addto@hook\toks@\NoValue
+      #1\XD@endgrab
+   }%
+}
+%    \end{macrocode}
+%   |\XD@grab@oarg@| is a helper to remove the brackets around the 
+%   optional argument.
+%    \begin{macrocode}
+\long\def\XD@grab@oarg@#1[#2]{%
+   \addto@hook\toks@{{#2}}%
+   #1\XD@endgrab
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@grab@sarg}
+%   A grabber for `star'-type arguments (\texttt{s} arguments in 
+%   \package{xparse}). The syntax is
+%   \begin{quote}
+%     |\XD@grab@sarg|\marg{char}
+%   \end{quote}
+%   It looks ahead to see if the next character is the \meta{char}. In 
+%   that case it gobbles it and adds a |\BooleanTrue| to the grabbed 
+%   arguments, otherwise it adds a |\BooleanFalse| to the grabbed 
+%   arguments.
+%   \changes{prot2.3}{2001/11/03}{Macro added. (LH)}
+%    \begin{macrocode}
+\def\XD@grab@sarg#1#2\XD@endgrab{%
+   \@ifnextchar#1{%
+      \addto@hook\toks@\BooleanTrue
+      \@firstoftwo{#2\XD@endgrab}%
+   }{%
+      \addto@hook\toks@\BooleanFalse
+      #2\XD@endgrab
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\XD@grab@withprivate}
+%   |\XD@grab@withprivate| is like |\XD@grab@marg| but grabs the 
+%   argument when the catcodes are as set by |\MakePrivateLetters|.
+%    \begin{macrocode}
+\def\XD@grab@withprivate{%
+   \begingroup\MakePrivateLetters\relax\expandafter\endgroup
+   \XD@grab@marg
+}
+%    \end{macrocode}
+%   To think about: Perhaps things like |\XD@grab@withprivate| should 
+%   rather be considered a modifier for a grabber? Instead of having 
+%   |\XD@grab@withprivate| be the entire grabber, one could let the 
+%   grabber be something like
+%   \begin{quote}
+%     |\XD@grab@withprivate\XD@grab@marg|
+%   \end{quote}
+%   where the |\XD@grab@withprivate| should only expand to
+%   \begin{quote}
+%     |\begingroup\MakePrivateLetters\relax\expandafter\endgroup|
+%   \end{quote}
+% \end{macro}
+% 
+% \begin{macro}{\XD@grab@asmacro}
+%   |\XD@grab@asmacro| is very similar to |\XD@grab@withprivate|, but it 
+%   sees to that the catcode settings are exactly those used by 
+%   \package{doc}'s \texttt{macro} environment.
+%    \begin{macrocode}
+\def\XD@grab@asmacro{%
+   \begingroup
+      \catcode`\\=12 \MakePrivateLetters\relax
+   \expandafter\endgroup
+   \XD@grab@marg
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\XD@grab@harmless}
+% \begin{macro}{\XD@grab@harmless@oarg}
+%   \changes{prot2.1}{2000/09/30}{Macro added. (LH)}
+% \begin{macro}{\XD@grab@harmless@oarg@}
+%   \changes{prot2.1}{2000/09/30}{Macro added. (LH)}
+%   The |\XD@grab@harmless| grabber grabs one mandatory argument and 
+%   converts it to a harmless character string, which it contributes to 
+%   the list of arguments. The syntax is
+%   \begin{quote}
+%     |\XD@grab@harmless|\marg{post-processing}
+%   \end{quote}
+%   where \meta{post-processing} are commands that will be performed 
+%   after the grabbed argument has been made harmless, but before it is 
+%   contributed to the list of arguments. Thus the 
+%   \meta{post-processing} can modify the argument some more, but 
+%   \meta{post-processing} can just as well be empty.
+%    \begin{macrocode}
+\def\XD@grab@harmless#1#2\XD@endgrab#3{%
+   \MakeHarmless\@tempa{#3}%
+   #1%
+   \toks@=\expandafter{\the\expandafter\toks@ \expandafter{\@tempa}}%
+   #2\XD@endgrab
+}
+%    \end{macrocode}
+%   
+%   The |\XD@grab@harmless@oarg| grabber grabs one optional argument and 
+%   converts it to a harmless character string. This string is 
+%   contributed to the list of arguments if the optional argument, or 
+%   else the token |\NoValue| is contributed instead.
+%    \begin{macrocode}
+\def\XD@grab@harmless@oarg#1\XD@endgrab{%
+   \@ifnextchar[{\XD@grab@harmless@oarg@{#1}}{%
+      \addto@hook\toks@\NoValue
+      #1\XD@endgrab
+   }%
+}
+%    \end{macrocode}
+%   |\XD@grab@harmless@oarg@| is a helper to remove the brackets around 
+%   the optional argument.
+%    \begin{macrocode}
+\long\def\XD@grab@harmless@oarg@#1[#2]{%
+   \MakeHarmless\@tempa{#2}%
+   \toks@=\expandafter{\the\expandafter\toks@ \expandafter{\@tempa}}%
+   #1\XD@endgrab
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@grab@harmless@asmacro}
+% \begin{macro}{\XD@grab@harmless@cs}
+% \begin{macro}{\XD@grab@harmless@cs@}
+%   The |\XD@grab@harmless@asmacro| grabber combines the features of 
+%   |\XD@grab@|\B|asmacro| and |\XD@grab@harmless|, since when the 
+%   argument to grab is tokenized the catcode of |\| is set to 12 and 
+%   the catcode assignments in |\MakePrivateLetters| are made. Then the 
+%   grabbed argument is converted to a harmless character sequence, and 
+%   finally the first character is removed if it is a backslash.
+%    \begin{macrocode}
+\def\XD@grab@harmless@asmacro{%
+   \begingroup
+      \catcode`\\=12 \MakePrivateLetters\relax
+   \expandafter\endgroup
+   \XD@grab@harmless{%
+      \protected@edef\@tempa{%
+         \expandafter\XD@unbackslash\@tempa\@empty
+      }%
+   }%
+}
+%    \end{macrocode}
+%   
+%   The |\XD@grab@harmless@cs| grabber is for use with commands like 
+%   \package{doc}'s |\Describe|\-|Macro|, which take an actual control 
+%   sequence as the argument. It grabs one argument while having 
+%   catcodes changed as indicated by |\Make|\-|Private|\-|Letters|, 
+%   |\string|s the argument while |\escapechar| is |-1| (so that there 
+%   is no escape character inserted), and continues as 
+%   |\XD@grab@harmless|.
+%    \begin{macrocode}
+\def\XD@grab@harmless@cs{%
+   \begingroup
+      \MakePrivateLetters\relax
+   \expandafter\endgroup \XD@grab@harmless@cs@
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\long\def\XD@grab@harmless@cs@#1\XD@endgrab#2{%
+   \begingroup
+      \escapechar=\m@ne
+   \expandafter\endgroup
+   \expandafter\MakeHarmless \expandafter\@tempa 
+      \expandafter{\string#2}%
+   \toks@=\expandafter{\the\expandafter\toks@ \expandafter{\@tempa}}%
+   #1\XD@endgrab
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@grab@harmless@withprivate}
+%   |\XD@grab@harmless@withprivate| is like |\XD@grab@harmless| but 
+%   grabs the argument when the catcodes are as set by 
+%   |\Make|\-|Private|\-|Letters|. 
+%   Like |\XD@|\B|grab@|\B|harmless|, |\XD@grab@|\B|harmless@|\B
+%   |withprivate| takes an argument which can contain code that 
+%   modifies the harmless character string after it has been formed.
+%    \begin{macrocode}
+\def\XD@grab@harmless@withprivate{%
+   \begingroup\MakePrivateLetters\relax\expandafter\endgroup
+   \XD@grab@harmless
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \subsection{The \cs{XD@m@cro} and \cs{NewMacroEnvironment} commands}
+% 
+% In \package{doc} the macro that contains most of the code for the 
+% \texttt{macro} and \texttt{environment} environments is called 
+% |\m@cro@|. In \package{xdoc} the corresponding macro is |\XD@m@cro|.
+% 
+% At this point, it is helpful to recall what |\m@cro@| actually does. 
+% It can be summarized in the following four points:
+% \begin{itemize}
+%   \item It starts a |\trivlist|.\footnote{Seriously, can someone 
+%     explain to me why it seems just about every non-math \LaTeX\ 
+%     environment that doesn't start a \cs{list} starts a \cs{trivlist}? 
+%     What good does all these \cs{trivlist}s do? Is it (a)~that people 
+%     just like the basic design, (b)~that there's some deep technical 
+%     reason, or (c)~that people in general doesn't have a clue but all 
+%     other environments do that so it's best to include it just in 
+%     case?}
+%   \item It prints the name of the macro\slash environment that is 
+%     about to be defined in the margin.
+%   \item It writes an index entry (and inhibits cross-referencing of 
+%     the macro inside the environment).
+%   \item It sets |\saved@macroname| to the name of the macro\slash 
+%     environment (for use by |\changes|).
+% \end{itemize}
+% 
+% The first and fourth points are simple, and commands for the third 
+% were defined in Section~\ref{Sec:Indexing}, but the second point 
+% needs a few helper macros.
+% 
+% 
+% \begin{macro}{\XDStackItemLabels}
+%   \changes{prot2}{2000/07/28}{Made it work like a \cs{vtop} (but hide 
+%      the height) if \cs{XD@macro@dimen} is \texttt{-}\cs{maxdimen}. 
+%      (LH)}
+% \begin{macro}{\XD@macro@dimen}
+%   The |\XDStackItemLabels| macro is a definition of |\makelabel| which 
+%   is used in the \texttt{macro}-like environments for stacking the 
+%   names printed by subsequent environments under each other. It makes 
+%   a box which has zero height and depth (it should have zero width as 
+%   well, but that is left as a restriction on the argument) and the 
+%   printed names will be stacked if the reference points of the 
+%   subsequent boxes generated by |\XD|\-|Stack|\-|Item|\-|Labels| 
+%   coincide.
+%   
+%   |\XD@macro@dimen| (always assigned globally) stores the vertical 
+%   distance from the reference point of the box that 
+%   |\XD|\-|Stack|\-|Item|\-|Labels| makes to the (bottommost) baseline 
+%   of the previous printed name. |\XD@macro@dimen| is updated by each 
+%   new |\XD|\-|Stack|\-|Item|\-|Labels|. The baseline of the next printed 
+%   name will be put one |\baselineskip| lower than that of the previous 
+%   printed name, except for when |\XD@macro@dimen| is |-\maxdimen| (see 
+%   below). To avoid that printed names clash into each other, this 
+%   additional |\baselineskip| is generated as normal interline glue 
+%   where the upper box has the same depth as a strut and the new value 
+%   of |\XD@macro@dimen| is measured in such a way that the printed 
+%   name's depth below the nominal baseline will not exceed the depth of 
+%   a strut (that's what the |\boxmaxdepth| assignment is for). 
+%   When |\XD@macro@dimen| is |-\maxdimen| the (topmost) baseline of the 
+%   printed name will instead go through the reference point of the box. 
+%   This case is intended for the first item label in a stack.
+%   
+%   The reason |\everypar| is cleared is that that is where the list 
+%   environments put the commands which actually insert the item label 
+%   into the paragraph. If that code gets executed inside |\makelabel|, 
+%   the list environments get seriously confused with not at all nice 
+%   consequences.
+%    \begin{macrocode}
+\def\XDStackItemLabels#1{%
+   \setbox\z@=\vbox{%
+      \ifdim \XD@macro@dimen=-\maxdimen
+         \setbox\z@=\vtop{%
+            \color@begingroup
+            \everypar={}%
+            #1%
+            \color@endgroup
+         }%
+         \kern-\ht\z@
+         \unvbox\z@
+      \else
+         \color@begingroup
+         \everypar={}%
+         \kern\XD@macro@dimen
+         \setbox\z@=\copy\strutbox \ht\z@=\z@ \box\z@
+         #1%
+         \color@endgroup
+      \fi
+      \boxmaxdepth=\dp\strutbox
+   }%
+   \global\XD@macro@dimen=\ht\z@
+   \vtop to\z@{\unvbox\z@ \vss}%
+}
+%    \end{macrocode}
+%    \begin{macrocode}
+\newdimen\XD@macro@dimen
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\XDToMargin}
+%   \changes{prot2.1}{2000/11/26}{New name for \cs{XD@to@margin}. (LH)}
+%   The |\XDToMargin| macro takes one argument, which is assumed to be 
+%   some horizontal material, and puts that material in a |\hbox| of 
+%   width zero, horizontally shifted out into the the outer margin, in 
+%   such a way that longer arguments extend further out. |\marginparsep| 
+%   is used as the distance between the argument and the main galley. All 
+%   these placements assume that the |\hbox| will be put |\labelsep| to 
+%   the left of the beginning of a nonindented paragraph, since that is 
+%   where it will be put by the |\item| of a |\trivlist|.
+%   
+%   A question is where the margin should be considered to start if the 
+%   |\@total|\-|left|\-|margin| isn't zero. The corresponding 
+%   \package{doc} action would be to consider the margin as everything 
+%   outside the |\linewidth| width, but I don't think that would be 
+%   appropriate here (especially not since \package{doc} always puts the 
+%   codeline numbers at the edge of the |\textwidth| width).
+%    \begin{macrocode}
+\newcommand\XDToMargin[1]{%
+   \hb@xt@\z@{%
+      \IfOddPageSituation{%
+         \dimen@=-\@totalleftmargin
+         \advance \dimen@ \labelsep
+         \advance \dimen@ \textwidth
+         \advance \dimen@ \marginparsep
+         \kern\dimen@
+      }\hss
+      #1%
+      \IfOddPageSituation\hss{%
+         \dimen@=\@totalleftmargin
+         \advance \dimen@ -\labelsep
+         \advance \dimen@ \marginparsep
+         \kern\dimen@
+      }%
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\XDParToMargin}
+%   The |\XDParToMargin| command is in syntax and use similar to the 
+%   |\XDToMargin| command, but it will try to linebreak an argument 
+%   that is too long rather than letting it extend outside the paper.
+%   
+%   The implementation first tries to break the argument without 
+%   considering justification or positioning, but with a rather high 
+%   |\linepenalty|. If the result of that try is a single line paragraph 
+%   then |\XDToMargin| will be called to actually typeset the argument. 
+%   Otherwise the argument is typeset as a paragraph which gets 
+%   displaced out into the outer margin by giving |\leftskip| and 
+%   |\rightskip| nonzero natural widths. The practical line width in 
+%   the paragraph is the |\marginparwidth|, but the hboxes containing 
+%   the individual lines will have width zero. The first line of the 
+%   paragraph will be set flush outwards, the last line of the paragraph 
+%   will be set flush inwards, and the remaining lines will be centered.
+%   
+%   \changes{prot2.1}{2000/11/26}{Command added. (LH)}
+%    \begin{macrocode}
+\newcommand\XDParToMargin[1]{%
+   \parindent=\z@
+   \setbox\z@=\vbox{%
+      \leftskip=\z@skip
+      \rightskip=\z@\@plus 1fil%
+      \parfillskip=\z@skip
+      \hsize=\marginparwidth
+      \linepenalty=1000%
+      \color@begingroup
+      \noindent\ignorespaces #1\@@par
+      \color@endgroup
+   \expandafter}%
+   \expandafter\ifnum \the\prevgraf<\tw@
+      \XDToMargin{#1}%
+   \else
+      \hsize=\z@
+      \leftskip=\z@ \@plus \marginparwidth
+      \rightskip=\leftskip
+      \IfOddPageSituation{%
+         \dimen@=-\@totalleftmargin
+         \advance \dimen@ \labelsep
+         \advance \dimen@ \textwidth
+         \advance \dimen@ \marginparsep
+         \advance \leftskip \dimen@
+         \advance \rightskip -\dimen@ \@minus \p@
+         \advance \rightskip -\marginparwidth
+         \parfillskip=\z@ \@plus 1fil%
+      }{%
+         \dimen@=\@totalleftmargin
+         \advance \dimen@ -\labelsep
+         \advance \dimen@ \marginparsep
+         \advance \leftskip -\dimen@ \@minus \p@
+         \advance \leftskip -\marginparwidth
+         \advance \rightskip \dimen@
+         \parfillskip=\z@ \@plus -\marginparwidth%
+      }
+      \noindent\nobreak\hskip\parfillskip
+      \ignorespaces #1\@@par
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+%   
+% In the following I exploit the implementation of the |\item| command 
+% in a slightly hackish way. Instead of starting a new paragraph with 
+% the item label (which is what one at first would believe |\item| 
+% does), |\item| actually puts the label in the box |\@labels| register, 
+% and stores code in |\everypar| that inserts that box into the new 
+% paragraph. Therefore I can make sure that various |\write| whatsits 
+% that need to be as the same page as an |\item| label will be there by 
+% adding them to the contents of the |\@labels| box. This seems more 
+% reliable to me than putting them on the vertical list followed by a 
+% |\nobreak| as \package{doc} does, but that would probably work as 
+% well.
+% 
+% [A funny thing in that which confused me a while was the question of 
+% whether the |\box| command that inserts the box into the paragraph and 
+% simultaneously clears the register acted globally or locally. It turns 
+% out that the question was ill-posed, as the distinction between local 
+% and global assignments is determined by what restore items they put 
+% on \TeX's save stack. The |\box| command doesn't put anything there, 
+% so the assignment it makes will essentially appear at the same 
+% grouping level as the |\setbox| command that set the contents of the 
+% box register. As all |\setbox|es for the |\@labels| box register are 
+% global, the box register will be globally void after |\box\@labels|.]
+% 
+% 
+% \begin{macro}{\XD@m@cro}
+%   \changes{prot2}{2000/07/24}{Put the \meta{changes} argument before 
+%      the \meta{assign} argument. Executing the \meta{assign} code 
+%      after the \meta{changes} \cs{edef}. Changed the descriptions of 
+%      these arguments a little. (LH)}
+%   \changes{prot2.1}{2000/11/26}{Removed \cs{XDToMargin} from the 
+%      argument of \cs{item}. It should now be included in \#1 
+%      instead. (LH)}
+%   This is the workhorse of all the \texttt{macro}-like environments. 
+%   It calls |\trivlist| and sets related parameters, prints the 
+%   ``macro'' name in the proper place, updates the representation of 
+%   the ``macro'' name that |\changes| will use, and writes appropriate 
+%   index entries (possibly making temporary changes in 
+%   cross-referencing). Exactly what these tasks consist of can vary 
+%   quite a lot between different \texttt{macro}-like environments, and 
+%   therefore the |\XD@m@cro| macro has the following syntax:
+%   \begin{quote}
+%     |\XD@m@cro|\marg{print}\marg{index}\marg{changes}\marg{assign}
+%   \end{quote}
+%   \meta{print}, \meta{index}, and \meta{assign} are simply the 
+%   commands for printing the ``macro'' name as it should appear in the 
+%   margin, generating the index entries for this \texttt{macro}-like 
+%   environment, and making whatever additional local assignments that 
+%   are needed for this environment (usually a couple of 
+%   |\Do|\-|Not|\-|Index|\-|Harmless| commands, if anything at all) 
+%   respectively. At the time \meta{index} is executed, 
+%   \texttt{codelineno} holds the number of the \emph{next} codeline. 
+%   \meta{changes}, finally, is code that will be put in the context
+%   \begin{quote}
+%     |\protected@edef\saved@macroname{|\meta{changes}|}|
+%   \end{quote}
+%   to set the |\saved@macroname| macro (for |\changes|).
+%    \begin{macrocode}
+\def\XD@m@cro#1#2#3#4{%
+   \topsep\MacroTopsep 
+   \trivlist
+   \global\setbox\@labels=\hbox{%
+      \unhbox\@labels
+      \if@inlabel \else
+         \global\XD@macro@dimen=-\maxdimen
+         \StepPageSituation
+         \RecordPageSituation
+      \fi
+      \advance \c@codelineno \@ne
+      #2%
+   }%
+   \let\makelabel\XDStackItemLabels
+   \item[#1]%
+   \protected@edef\saved@macroname{#3}%
+   #4%
+   \ignorespaces
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% In the first \package{xdoc} prototype, the \texttt{macro}-like 
+% environments were implemented so that each new environment only used 
+% two control sequences (|\|\meta{env} and |\end|\meta{env}), which is 
+% the absolute minimum. This implementation worked fine for 
+% single argument environments, but the number of helper macros that 
+% would have to be introduced to deal with multiple argument 
+% environments exceeded what could be considered reasonable. Therefore 
+% the second prototype claims a third control sequence for the 
+% implementation of a \texttt{macro}-like environment \meta{env}, namely 
+% |\\|\meta{env}, which is also used by normal \LaTeXe\ environments 
+% which take an optional argument.
+% 
+% It should also be mentioned that the implementation in the first 
+% prototype required that most of the code in |\|\meta{env} had to be 
+% written in a very special way. Instead of using the |#|\meta{digit} 
+% notation for the arguments and write straightforward \LaTeX\ code, one 
+% had to express everything using macros which operate on arguments ``up 
+% ahead'' (immediately after the code you can specify). This curious 
+% coding model made it out of the question to create a class designer 
+% interface for defining new \texttt{macro}-like environments, but in 
+% the second \package{xdoc} prototype it is quite simple to do something 
+% of that sort: the command name is |\New|\-|Macro|\-|Environment|.
+% 
+% \begin{macro}{\NewMacroEnvironment}
+%   \changes{prot2}{2000/07/13}{Command added. (LH)}
+%   \changes{prot2}{2000/07/24}{Changed syntax in conformity with the 
+%      syntax change in \cs{XD@m@cro}. (LH)}
+%   \changes{prot2.1}{2000/11/26}{Introduced star form with different 
+%      semanics for the \meta{print} argument. This uses the helper 
+%      macros \cs{XD@NewMacroEnvironment} and 
+%      \cs{XD@NewMacroEnvironment@}. (LH)}
+% \begin{macro}{\XD@NewMacroEnvironment}
+% \begin{macro}{\XD@NewMacroEnvironment@}
+%   The |\NewMacroEnvironment| command is used for defining new 
+%   \texttt{macro}-like environments. It has the syntaxes
+%   \begin{quote}
+%     |\NewMacroEnvironment|\marg{name}\marg{grabbers}\marg{numargs}\\
+%     \vadjust{}\hfill\marg{unjust-print}\marg{index}\marg{changes}^^A
+%     \marg{assign}\\
+%     |\NewMacroEnvironment*|\marg{name}\marg{grabbers}\marg{numargs}\\
+%     \vadjust{}\hfill\marg{print}\marg{index}\marg{changes}\marg{assign}
+%   \end{quote}
+%   where \meta{name} is the name of the environment to define, 
+%   \meta{grabbers} is a sequence of argument grabbers, \meta{numargs} 
+%   is the number of arguments that the grabbers will grab, and
+%   \meta{print}, \meta{index}, \meta{changes}, and \meta{assign} are 
+%   code that will be put in the respective arguments of |\XD@m@cro|. 
+%   In the four last arguments, argument specifiers |#1| to 
+%   |#|\meta{numargs} inclusive can be used do mean the arguments that 
+%   were grabbed by the sequence of grabbers.
+%   
+%   The argument grabbers that are currently made available by the 
+%   \package{xdoc} package are listed in Table~\ref{Tab:Grabbers} on 
+%   page~\pageref{Tab:Grabbers}.
+%   
+%   The \meta{print} code will be executed while \TeX\ is in internal 
+%   vertical mode and it should put one or several hboxes of width zero 
+%   onto the vertical list. The contents of these boxes should be some 
+%   amount of text which will appear displaced out into the outer margin 
+%   on the page when the reference point of the box appears |\labelsep| 
+%   to the left of the left edge of the line. The easiest way of 
+%   achieveing this is to use a \meta{print} of the form
+%   \begin{quote}
+%     |\XDToMargin|\marg{unjust-print}
+%   \end{quote}
+%   and this is exactly what the non-star form of |\NewMacroEnvironment| 
+%   does by default.
+%   
+%    \begin{macrocode}
+\newcommand\NewMacroEnvironment{%
+   \@ifstar\XD@NewMacroEnvironment\XD@NewMacroEnvironment@
+}
+\def\XD@NewMacroEnvironment@#1#2#3#4{%
+   \XD@NewMacroEnvironment{#1}{#2}{#3}{\XDToMargin{#4}}%
+}
+\def\XD@NewMacroEnvironment#1#2#3#4#5#6#7{%
+   \expandafter\@ifdefinable\csname#1\endcsname{%
+      \expandafter\def \csname#1\expandafter\endcsname
+         \expandafter{\expandafter\XD@grab@arguments
+         \csname\@backslashchar#1\endcsname{#2}}%
+      \let\l@ngrel@x\relax
+      \expandafter\@yargdef \csname\@backslashchar#1\endcsname \@ne
+         {#3}{\XD@m@cro{#4}{#5}{#6}{#7}}%
+      \expandafter\let \csname end#1\endcsname \endtrivlist
+   }%
+}
+%    \end{macrocode}
+%   The \meta{grabbers} argument---in which one specifies a list of 
+%   internal macros---is not how the interface should really look, but I 
+%   think it will have to do for now. The final interface will probably 
+%   use something like the argument specifications of 
+%   |\Declare|\-|Document|\-|Command|, but there is little point in 
+%   implementing that before \package{xparse} has gotten its final form.
+% \end{macro}\end{macro}\end{macro}
+% 
+% The macro |\@yargdef| used above should perhaps be checked so that its 
+% syntax hasn't changed, but since |\@yargdef| quite recently 
+% (\texttt{ltdefn.dtx} v\,1.3c, 1999/01/18) was completely reimplemented 
+% without any change in the syntax (despite the fact that the syntax is 
+% afterwards rather peculiar), I think it can be assumed that the syntax 
+% will not change in \LaTeXe.
+% 
+% 
+% 
+% \subsection{Reimplementing \texttt{macro} and \texttt{environment}}
+% \label{Ssec:Macro&environment}
+% 
+% Well, then how does one reimplement the \texttt{macro} and 
+% \texttt{environment} environments using |\XD@m@cro|? We shall soon 
+% see, but first it is convenient to define a utility macro.
+% 
+% \changes{prot2}{2000/07/14}{Lots of utility macros were removed: 
+%    \cs{XDWrapText}, \cs{XDAltWrapText}, \cs{XDSortAndText}, 
+%    \cs{MultipleApply}, \cs{ApplicableUsageIndex}, and 
+%    \cs{XD@index@family}. (LH)}
+% 
+% \begin{macro}{\XDMainIndex}
+%   \changes{prot2}{2000/07/14}{New name and syntax for 
+%     \cs{ApplicableMainIndex}. (LH)}
+%   The |\XDMainIndex| macro is an abbreviation to save a couple of 
+%   tokens in a very frequent call to |\IndexEntry|. It has the syntax
+%   \begin{quote}
+%     |\XDMainIndex|\marg{argument}
+%   \end{quote}
+%   and that expands to
+%   \begin{quote}
+%     |\IndexEntry|\marg{argument}|{main}{\TheXDIndexNumber}|
+%   \end{quote}
+%    \begin{macrocode}
+\newcommand\XDMainIndex[1]{\IndexEntry{#1}{main}{\TheXDIndexNumber}}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{environment}{macro}
+%   \changes{prot2.1}{2000/11/15}{Using \cs{MakeSortKey} to make index 
+%      entry. (LH)}
+% \begin{environment}{environment}
+%   It is very easy to implement \texttt{macro} and \texttt{environment} 
+%   environments which behave pretty much as in \package{doc} using the 
+%   |\New|\-|Macro|\-|Environment| command. The important difference 
+%   is that in \package{doc} everything that distinguished the two 
+%   environments was to be found in various helper macros, but here all 
+%   that code is in the |\\macro| and |\\environment| macros. Thus to 
+%   define one new \texttt{macro}-like environment, one doesn't have to 
+%   define six or so new macros---everything can be handled in one 
+%   definition.
+%   
+%   The reason for the |\let| commands below is of course that 
+%   \texttt{macro} and \texttt{environment} are already defined, and 
+%   there is no |\Renew|\-|Macro|\-|Environment| command. It could 
+%   perhaps have been better if |\New|\-|Macro|\-|Environment|  had 
+%   behaved like |\Declare|\-|Robust|\-|Command|, but I don't think that 
+%   is an important problem for the moment.
+%    \begin{macrocode}
+\let\macro=\relax
+\let\endmacro=\relax
+\NewMacroEnvironment{macro}{\XD@grab@harmless@asmacro}{1}
+   {\MacroFont\Bslash#1}
+   {\MakeSortKey\@tempa{#1}{}%
+    \XDMainIndex{\LevelSorted{\@tempa}{\texttt{\Bslash#1}}}}
+   {{#1}{\texttt{\Bslash#1}}}
+   {\DoNotIndexHarmless{#1}}
+%    \end{macrocode}
+%    \begin{macrocode}
+\let\environment=\relax
+\let\endenvironment=\relax
+\NewMacroEnvironment{environment}{\XD@grab@harmless@asmacro}{1}
+   {\MacroFont#1}
+   {\XDMainIndex{\LevelSorted{#1}{\texttt{#1} (environment)}}%
+    \XDMainIndex{%
+       \LevelSame{environments:}\LevelSorted{#1}{\texttt{#1}}%
+   }}%
+   {{#1}{\texttt{#1}}}
+   {}%
+%    \end{macrocode}
+% \end{environment}\end{environment}
+% 
+% 
+% \subsection{Further examples of \texttt{macro}-like environments}
+% \label{Ssec:More macros}
+% 
+% \begin{environment}{option}
+%   The \texttt{option} environment is for class\slash package options. 
+%   IMHO, something like this environment should have been added to 
+%   \package{doc} years ago!
+%   
+%    \begin{macrocode}
+\NewMacroEnvironment{option}{\XD@grab@harmless\relax}{1}
+   {\MacroFont#1 \normalfont option}
+   {\XDMainIndex{\LevelSorted{#1}{\texttt{#1} option}}%
+    \XDMainIndex{%
+       \LevelSame{options:}\LevelSorted{#1}{\texttt{#1}}%
+   }}%
+   {{#1 option}{\texttt{#1} option}}
+   {}%
+%    \end{macrocode}
+% \end{environment}
+% 
+% \begin{environment}{switch}
+%   \changes{prot2.1}{2000/11/18}{Using \cs{MakeSortKey}. (LH)}
+%   The \texttt{switch} environment is for switches created by 
+%   |\newif| (\PlainTeX\ style).
+%    \begin{macrocode}
+\NewMacroEnvironment{switch}{\XD@grab@harmless\relax}{1}
+   {\MacroFont#1 \normalfont switch}%
+%    \end{macrocode}
+%   What makes switches different from the other \texttt{macro}-like 
+%   environments defined here is the large number of index entries it 
+%   makes. For a switch \meta{sw} it first makes one under the `switches:' 
+%   heading:
+%    \begin{macrocode}
+   {%
+      \MakeSortKey\XD@last@key{#1}{}%
+      \XDMainIndex{%
+         \LevelSame{switches:}\LevelSorted{\XD@last@key}{\texttt{#1}}%
+      }%
+%    \end{macrocode}
+%   Second it makes a `\meta{sw} switch' entry:
+%    \begin{macrocode}
+      \XDMainIndex{\LevelSorted{\XD@last@key}{\texttt{#1} switch}}%
+%    \end{macrocode}
+%   Third it makes an entry for the macro |\if|\meta{sw}. The sort key 
+%   for this entry is \emph{not} subjected to |\MakeSortKey| because 
+%   no reasonable operator will act on the |if| prefix (an operator 
+%   which acts on |if| could do rather strange things to e.g. |\ifnum|).
+%    \begin{macrocode}
+      \XDMainIndex{\LevelSorted{if#1}{\texttt{\Bslash if#1}}}%
+%    \end{macrocode}
+%   Fourth it makes an entry for the macro |\|\meta{sw}|false|:
+%    \begin{macrocode}
+      \MakeSortKey\@tempa{#1false}{}%
+      \XDMainIndex{\LevelSorted{\@tempa}{\texttt{\Bslash#1false}}}%
+%    \end{macrocode}
+%   Finally it makes an entry for the macro |\|\meta{sw}|true|:
+%    \begin{macrocode}
+      \MakeSortKey\@tempa{#1true}{}%
+      \XDMainIndex{\LevelSorted{\@tempa}{\texttt{\Bslash#1true}}}%
+   }%
+%    \end{macrocode}
+%   The |\changes| heading, on the other hand, is trivial.
+%    \begin{macrocode}
+   {{#1}{\texttt{#1} switch}}
+%    \end{macrocode}
+%   Finally, \texttt{switch} should turn off indexing of the three macros 
+%   it makes \texttt{main} entries for, since \package{makeindex} will 
+%   otherwise complain.
+%    \begin{macrocode}
+   {\DoNotIndexHarmless{if#1}%
+    \DoNotIndexHarmless{#1false}%
+    \DoNotIndexHarmless{#1true}}%
+%</pkg>
+%    \end{macrocode}
+% \end{environment}
+% 
+% 
+% To end this section, there now follows two examples which are not 
+% part of the package as they are very specific, but which have been 
+% included here because they illustrate that \texttt{macro}-like 
+% environments may have several arguments.
+% 
+% \begin{environment}{enccommand}
+% \begin{environment}{enccomposite}
+%   The \texttt{enccommand} and \texttt{enccomposite} environments can 
+%   be used for marking up sources for encoding definition files and the 
+%   like. \texttt{enccommand} is for encoding-specific commands and has 
+%   the syntax
+%   \begin{quote}
+%     |\begin{enccommand}|\marg{command}\oarg{encoding}
+%   \end{quote}
+%   where \meta{command} is the encoding-specific command and 
+%   \meta{encoding} is the encoding that this definition is for. If the 
+%   \meta{encoding} is omitted then the \texttt{enccommand} is assumed 
+%   to be for the default definition of the command.
+%   
+%   \texttt{enccomposite} is for composites of encoding-specific 
+%   commands (defined for example using |\Declare|\-|Text|\-|Composite|). 
+%   It has the syntax
+%   \begin{quote}
+%     |\begin{enccomposite}|\marg{command}\marg{encoding}\marg{argument}
+%   \end{quote}
+%   where \meta{command} and \meta{encoding} are as for 
+%   \texttt{enccommand} and \meta{argument} is the argument with which 
+%   the command is being composed.
+%   
+%   The marginal headings these commands print are the actual control 
+%   sequences in which the definitions are stored.
+%    \begin{macrocode}
+%<*enccmds>
+\NewMacroEnvironment{enccommand}{%
+   \XD@grab@harmless@asmacro \XD@grab@oarg
+}{2}{\MacroFont\Bslash \ifx\NoValue#2?\else#2\fi \Bslash #1}{%
+   \XDMainIndex{%
+      \LevelSorted{#1}{\texttt{\Bslash#1}}%
+      \ifx \NoValue#2%
+         \LevelSame{default}%
+      \else
+         \LevelSorted{#2}{\texttt{#2} encoding}%
+      \fi
+   }%
+}{{#1}{\texttt{\Bslash#1}}}{\DoNotIndexHarmless{#1}}
+%    \end{macrocode}
+%    \begin{macrocode}
+\NewMacroEnvironment{enccomposite}{%
+   \XD@grab@harmless@asmacro \XD@grab@marg \XD@grab@harmless\relax
+}{3}{\MacroFont\Bslash#2\Bslash#1-#3}{%
+   \XDMainIndex{%
+      \LevelSorted{#1}{\texttt{\Bslash#1}}%
+      \LevelSorted{#2}{\texttt{#2} encoding}%
+      \LevelSorted{\XD@unbackslash#3\@empty}{\texttt{#3} composite}%
+   }%
+}{{#1}{\texttt{\Bslash#1}}}{\DoNotIndexHarmless{#1}}
+%</enccmds>
+%    \end{macrocode}
+%   In the file \texttt{cyoutenc.dtx} the definitions of many 
+%   encoding-specific commands are written so that the same line of 
+%   code can work is all four files \texttt{t2aenc.def}, 
+%   \texttt{t2benc.def}, \texttt{t2cenc.def}, and \texttt{x2enc.def}. 
+%   Therefore the \meta{encoding} argument of the \texttt{enccommand} 
+%   and \texttt{enccomposite} environments should perhaps rather be a 
+%   comma-separated list of encodings than a single encoding, but that 
+%   would make this example unnecessarily complicated.
+% \end{environment}\end{environment}
+% 
+% 
+% 
+% \section{Describing macros and the like}
+% \label{Sec:Describing}
+% 
+% \begin{macro}{\if@mparswitch}
+% \begin{macro}{\if@reversemargin}
+%   In two-sided mode, marginal notes should appear in the outer 
+%   margin. The following code takes care of that.
+%    \begin{macrocode}
+%<*pkg>
+\if@twoside
+   \@mparswitchtrue
+   \normalmarginpar
+\fi
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\GenericDescribePrint}
+%   \changes{prot2}{2000/07/14}{\cs{leavevmode} and \cs{ignorespaces} 
+%      moved to \cs{NewDescribeCommand}. (LH)}
+%   \changes{prot2}{2000/07/20}{Added \cs{strut}. Removed it from 
+%      arguments passed to \cs{GenericDescribePrint}. (LH)}
+%   \changes{prot2.3}{2001/06/24}{Changed formatting to match that of 
+%      \cs{XDParToMargin}. (LH)}
+%   The |\GenericDescribePrint| macro is a utility macro for use in 
+%   commands like |\Describe|\-|Macro|. Its syntax is
+%   \begin{quote}
+%     |\GenericDescribePrint|\marg{text}
+%   \end{quote}
+%   and it puts \meta{text} in a marginal paragraph, giving it the 
+%   appropriate justification for appearing in that margin.
+%   
+%   The first part simply tests whether the argument fits on a single 
+%   line.
+%    \begin{macrocode}
+\newcommand\GenericDescribePrint[1]{%
+   \setbox\z@=\vbox{%
+      \parindent=\z@
+      \leftskip=\z@skip
+      \rightskip=\z@\@plus 1fil%
+      \parfillskip=\z@skip
+      \hsize=\marginparwidth
+      \linepenalty=\@m
+      \color@begingroup
+      \noindent\ignorespaces #1\@@par
+      \color@endgroup
+   \expandafter}%
+   \expandafter\ifnum \the\prevgraf<\tw@
+%    \end{macrocode}
+%    Then comes the actual typesetting. First the single-line format. 
+%    The braces in the optional argument are there to prevent trouble 
+%    in case |#1| contains a right brace; they will be stripped off when 
+%    the argument is grabbed.
+%    \begin{macrocode}
+      \if@twoside
+         \marginpar[{\raggedleft\strut #1}]{\raggedright\strut #1}%
+      \else
+         \marginpar{\raggedleft\strut#1}%
+      \fi
+   \else
+      \if@twoside
+         \marginpar[{%
+            \leftskip=\z@ \@plus \marginparwidth
+            \rightskip=\leftskip
+            \parfillskip=\z@ \@plus -\marginparwidth
+            \noindent\nobreak\hskip\parfillskip
+            \ignorespaces #1%
+         }]{%
+            \leftskip=\z@ \@plus \marginparwidth
+            \rightskip=\leftskip
+            \parfillskip=\z@ \@plus 1fil%
+            \noindent\nobreak\hskip\parfillskip
+            \ignorespaces #1%
+         }%
+      \else
+         \marginpar{%
+            \leftskip=\z@ \@plus \marginparwidth
+            \rightskip=\leftskip
+            \parfillskip=\z@ \@plus -\marginparwidth
+            \noindent\nobreak\hskip\parfillskip
+            \ignorespaces #1%
+         }%
+      \fi
+   \fi
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% The \texttt{describe}-commands are supposed to be invisible---only 
+% leave a single space even when there are spaces both before and after 
+% them---but there are problems with the mechanisms for this. I get the 
+% impression that they have never worked perfectly, but that seems to 
+% be mainly due to that certain macros in the \LaTeX\ kernel never did 
+% either, and I suspect that the general problem has been thrashed over 
+% many times before.
+% 
+% \package{doc}'s |\DescribeMacro| and |\DescribeEnv| are wrapped up in 
+% a |\@bsphack| \dots\ |\@esphack| ``group'' to become invisible, but 
+% the |\marginpar| and various index commands they are built on are 
+% themselves already invisible, so one would suspect that there is no 
+% need for additional invisibility. There are however two factors which 
+% create this need. One is that it doesn't do the right thing at 
+% beginning of lines; here it seems like what the 
+% \texttt{describe}-commands would need is the |\@vbsphack| macro 
+% (whose definition appears in \texttt{ltspace.dtx}, but which has been 
+% commented out) since they should start a new paragraph and leave no 
+% following space if they are used in vertical mode. The other factor is 
+% that the standard |\@bsphack|--|\@esphack| can only suppress every 
+% second intermediate space if several invisible commands appear in 
+% sequence, as is quite common for the 
+% \texttt{describe}-commands.\footnote{It would seem that a simple fix 
+% for this is to have \cs{@esphack} insert \cs{nobreak} 
+% \cs{hskip}\texttt{-}\cs{@savsk} \cs{hskip}\cs{@savsk} before it 
+% executes \cs{ignorespaces}, but since that fix hasn't been 
+% incorporated into the kernel or the \package{fixltx2e} package there 
+% probably is some problem with it.}
+% 
+% Instead the \package{doc} implementations of |\DescribeMacro| and 
+% |\DescribeEnv| begin with |\leavevmode| and end with |\ignorespaces|, 
+% which means that they are only ``invisible'' if they appear on on the 
+% left of visible material, but that's how it has been for over a decade 
+% now.
+%  
+% \begin{macro}{\NewDescribeCommand}
+%   \changes{prot2}{2000/07/14}{Command added. (LH)}
+%   The |\NewDescribeCommand| command is a relative to the 
+%   |\New|\-|Macro|\-|Environment| command which defines commands 
+%   analogous to |\Describe|\-|Macro| rather than \texttt{macro}-like 
+%   environments. Its syntax is
+%   \begin{quote}
+%     |\NewDescribeCommand|\marg{command}\marg{grabbers}\B
+%     \marg{numargs}\B\marg{definition}
+%   \end{quote}
+%   \meta{command} is the control sequence to define. \meta{grabbers} 
+%   and \meta{numargs} are as for the |\NewMacroEnvironment| command. 
+%   \meta{definition} is the command definition.
+%   In addition to the definition given in the \meta{definition} 
+%   argument and the code for grabbing the arguments, the command 
+%   actually defined by |\New|\-|Describe|\-|Command| will contain a 
+%   |\leavevmode| at the start and an |\ignorespaces| at the end. 
+%   
+%   The |\NewDescribeCommand| command should really just be a call to 
+%   \package{xparse}'s |\Declare|\-|Document|\-|Command|, but that will 
+%   have to wait until \package{xdoc} becomes based on the 
+%   \package{xparse} package.
+%    \begin{macrocode}
+\newcommand\NewDescribeCommand[4]{%
+   \@ifdefinable#1{%
+      \expandafter\def \expandafter#1\expandafter{%
+         \expandafter\XD@grab@arguments \csname\string#1\endcsname{#2}%
+      }%
+      \let\l@ngrel@x\relax
+      \expandafter\@yargdef \csname\string#1\endcsname \@ne {#3}%
+         {\leavevmode#4\ignorespaces}%
+   }%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\DescribeMacro}
+%   \changes{prot2.1}{2000/11/18}{Using \cs{MakeSortKey}. (LH)}
+% \begin{macro}{\DescribeEnv}
+%   The |\DescribeMacro| and |\DescribeEnv| commands are as in 
+%   \package{doc}. The argument of |\DescribeMacro| is supposed to be 
+%   the actual control sequence to describe (not as with the 
+%   \texttt{macro} environment something which looks like the control 
+%   sequence after being |\string|ed).
+%    \begin{macrocode}
+\let\DescribeMacro=\relax
+\NewDescribeCommand\DescribeMacro{\XD@grab@harmless@cs}{1}{%
+   \GenericDescribePrint{\MacroFont\Bslash#1}%
+   \MakeSortKey\@tempa{#1}{}%
+   \IndexEntry{%
+      \LevelSorted{\@tempa}{\texttt{\Bslash#1}}%
+   }{usage}{\thepage}%
+}
+%    \end{macrocode}
+%   The argument of |\DescribeEnv|, on the other hand, is treated like 
+%   that of the \texttt{environment} environment, but backslash isn't 
+%   given catcode 12---only the catcode assignments in 
+%   |\Make|\-|Private|\-|Letters| are made.
+%    \begin{macrocode}
+\let\DescribeEnv=\relax
+\NewDescribeCommand\DescribeEnv{%
+   \XD@grab@harmless@withprivate\relax
+}{1}{%
+   \GenericDescribePrint{\MacroFont#1}%
+   \IndexEntry{%
+      \LevelSame{environments:}\LevelSorted{#1}{\texttt{#1}}%
+   }{usage}{\thepage}%
+   \IndexEntry{%
+      \LevelSorted{#1}{\texttt{#1} (environment)}%
+   }{usage}{\thepage}%
+}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\describeoption}
+%   \changes{prot2}{2000/07/31}{Command added---I realised that the need 
+%      to describe options is probably as large as that to mark out 
+%      their definition. (LH)}
+%   The |\describeoption| command is the \texttt{describe}-companion to 
+%   the \texttt{option} environment.
+%    \begin{macrocode}
+\NewDescribeCommand\describeoption{\XD@grab@harmless\relax}{1}{%
+   \GenericDescribePrint{\MacroFont#1 \normalfont option}%
+   \IndexEntry{%
+      \LevelSame{options:}\LevelSorted{#1}{\texttt{#1}}%
+   }{usage}{\thepage}%
+   \IndexEntry{%
+      \LevelSorted{#1}{\texttt{#1} option}%
+   }{usage}{\thepage}%
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \begin{macro}{\describecsfamily}
+%   \changes{prot2}{2000/07/14}{Renamed \cs{DescribeCSFamily} and 
+%      incorporated the code from \cs{XD@index@family}. (LH)}
+%   \changes{prot2.1}{2000/11/18}{Using \cs{MakeSortKey}. (LH)}
+%   The |\describecsfamily| command is for marking out sections in text 
+%   where a particular family of control sequences is described---just 
+%   like |\DescribeMacro| does for individual commands. To clarify what 
+%   I mean by a control sequence family, here are a couple of examples:
+%   \begin{longtable}{l >{\raggedright}p{0.55\linewidth}}
+%     |\c@|\meta{counter}\label{Tab:CS-families}& 
+%       countdef token for the |\count| register storing the 
+%       \LaTeX\ counter \meta{counter}\tabularnewline
+%     |\ps@|\meta{pagestyle}&
+%       macro storing settings for the pagestyle \meta{pagestyle}^^A
+%       \tabularnewline
+%     |\|\meta{enc}|/|\meta{fam}|/|\meta{ser}|/|\meta{sh}|/|\meta{sz}&
+%       the fontdef token for the font which has encoding \meta{enc}, 
+%       family \meta{fam}, series \meta{ser}, shape \meta{sh}, and 
+%       size \meta{sz} under NFSS\tabularnewline
+%     |\|\meta{enc}|\|\meta{cmd}&
+%       the macro containing the definition for encoding \meta{enc} of 
+%       the encoding-specific \LaTeX\ command |\|\meta{cmd}^^A
+%       \tabularnewline
+%     |\fps@|\meta{type}&
+%       the default placement specifier for \LaTeX\ floats of type 
+%       \meta{type}\tabularnewline
+%     |\l@|\meta{name}&
+%       a macro which formats table of contents entries for items of 
+%       type \meta{name} (\texttt{chapter}, \texttt{section}, etc.)^^A
+%       \tabularnewline
+%     |\l@|\meta{language}&
+%       the |\language| number \package{babel} has allocated for the 
+%         language \meta{language} (\texttt{english}, \texttt{french}, 
+%         etc.)\tabularnewline
+%     |\i-|\meta{int}&
+%       the control sequence (either a mathchardef token or a macro) 
+%       which stores the value of the \package{fontinst} integer 
+%       \meta{int}
+%   \end{longtable}
+%   
+%   The syntax for |\describecsfamily| is
+%   \begin{quote}
+%     |\describecsfamily|\marg{cs-fam specification}
+%   \end{quote}
+%   The \meta{cs-fam specification} includes only what would be put 
+%   between |\csname| and |\endcsname|; the |\describecsfamily| command 
+%   will add a backslash when printing the name. No special catcodes 
+%   will be in force in the argument, but the |#|, |$|, |&|, |_|, |^|, 
+%   and |~| characters present no problems even if they have their 
+%   ordinary catcodes. All spaces are seen as ASCII space and \TeX\ is 
+%   skipping spaces as usual. Characters with catcode 0, 1, 2, 5, 9, 14, 
+%   or 15 may however be problematic.
+%   If you need to specify such a problematic character then you can do 
+%   so by writing |\PrintChar|\marg{code}, where \meta{code} is the 
+%   ASCII code for the character, as a valid \TeX\ number in the range 
+%   0--255. In case you do not remember the ASCII code for some 
+%   character \meta{c}, there is no harm in specifying it as 
+%   |`\|\meta{c}, e.g. |\PrintChar{`\}}| for a right brace. It is even 
+%   possible to write |\PrintChar| commands for characters outside 
+%   visible ASCII (but those are typeset as |^^|-sequences).
+%   
+%   The variant parts in the control sequence names are specified as
+%   \begin{quote}
+%     |\meta|\marg{text}
+%   \end{quote}
+%   and these will be typeset exactly as in normal text. The arguments 
+%   of |\meta|s appearing in a \meta{cs-fam specification} are moving.
+%   All control sequences other than |\PrintChar| and |\meta| in a 
+%   \meta{cs-fam specification} (and which do not appear in the argument 
+%   of a |\PrintChar| or |\meta|) are essentially treated as if they 
+%   had been |\string|ed. 
+%   
+%   Apart from the above differences in treatment of the argument, the 
+%   |\describe|\-|cs|\-|family| command is similar to 
+%   |\DescribeMacro|---it prints the control sequence name in the margin 
+%   and makes a \texttt{usage} index entry.
+%    \begin{macrocode}
+\NewDescribeCommand\describecsfamily{\XD@grab@harmless{}}{1}{%
+   \GenericDescribePrint{%
+      \MetaNormalfont\MacroFont\Bslash#1%
+   }%
+   \MakeSortKey\@tempa{#1}{\def\meta##1{(##1)}}%
+   \IndexEntry{%
+      \LevelSorted{\@tempa}{\texttt{\protect\MetaNormalfont\Bslash#1}}%
+   }{usage}{\thepage}%
+}
+%</pkg>
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% As for |\NewMacroEnvironment|, I also give an example of an 
+% application of |\NewDescribeCommand| which is much too special for 
+% including in \package{xdoc} in general and therefore the code is 
+% placed in a special module. I had originally written the code as part 
+% of another package, but I removed it because I thought it was a bit 
+% too special even for that context. The commentry below is kept 
+% unchanged.\changes{prot2.1}{2000/09/16}{Additional 
+%    \cs{NewDescribeCommand} code example added. (LH)}
+% 
+% \begin{quotation}
+% 
+% I believe this feature is primarily of interest for MacOS programs, 
+% but there might be sufficiently similar structures in other operating 
+% systems to make it useful even in other contexts. Be as it may, what 
+% the feature described here does is that it allows the user to put an 
+% entry in the index for each resource in the code. This gives an easy 
+% way of checking that no two resources are assigned the same id, even 
+% though there is no mechanism for especially warning for such 
+% collisions.
+% 
+% \begin{macro}{\DescribeResource}
+%   The main command available is
+%   \begin{quote}
+%     |\DescribeResource|\marg{type}\marg{id}\marg{text}
+%   \end{quote}
+%   \meta{type} is a four-character string. Most special characters are 
+%   treated as ordinary ones (very useful for |#|s), but the visible 
+%   ASCII characters |%|, |{|, |\|, and |}| retain their usual meaning. 
+%   To use such a troublesome character \meta{c} in a resource type, 
+%   write it as |\PrintChar{`\|\meta{c}|}|. \meta{id} is a \TeX\ number; 
+%   it will be used as the number of the resource. \meta{text} is normal 
+%   text that will be put in the index entry to describe the resource; it 
+%   seems a good idea to use the name of the resource for this. \meta{id} 
+%   and \meta{text} are read with normal \LaTeX\ catcodes. Note that 
+%   \meta{text} is a moving argument.
+%   
+%   |\DescribeResource| does two things---it prints the \meta{type} and 
+%   \meta{id} of the resource in the margin, and it writes an entry
+%   \begin{quote}
+%     \meta{type} resources:\\
+%     \vadjust{}\qquad\meta{id}\\
+%     \vadjust{}\qquad\qquad\meta{text}
+%   \end{quote}
+%   (plus a lot of formatting not shown here) to the \texttt{.idx} file. 
+%   The reference is for the page.
+%   
+%   The idea with advancing |\count@| like that when constructing the 
+%   index entry is to get a sort key for which lexicographic order equals 
+%   the wanted order. This would not be the case if the number was simply 
+%   written down. The current code maps numbers to six-digit positive 
+%   integers, but five-digits integers would be sufficient (a resource 
+%   \meta{id} is a signed 16-bits integer). The construction chosen 
+%   here furthermore puts the negative numbers after the positive ones.
+%    \begin{macrocode}
+%<*rsrccmd>
+\NewDescribeCommand\DescribeResource{%
+   \XD@grab@harmless\relax \XD@grab@marg \XD@grab@marg
+}{3}{%
+   \GenericDescribePrint{#1%
+      \textnormal{:\ifnum#2<\z@ \textminus\number-\else\number\fi#2}%
+   }%
+   \count@=#2\relax
+   \advance \count@ 100000\ifnum \count@<\z@ 0\fi \relax
+   \protected@edef\@tempa{%
+      \noexpand\LevelSorted{\the\count@}{%
+         \ifnum #2<\z@ \string\textminus \number-\else\number\fi#2%
+      }%
+   }%
+   \IndexEntry{%
+      \LevelSorted{#1 resources:}{\texttt{#1} resources:}%
+      \@tempa
+      \LevelSame{#3}%
+   }{usage}{\thepage}%
+}
+%</rsrccmd>
+%    \end{macrocode}
+% \end{macro}
+% 
+% \end{quotation}
+% 
+% 
+% \section{The \cs{DocInclude} command}
+% \label{Sec:DocInclude}
+% 
+% The code in this section is based on code from the \package{ltxdoc} 
+% document class~\cite{ltxdoc} and it implements a command called 
+% |\DocInclude|. Two implementations of this command are given: one 
+% which is essentially that of \package{ltxdoc} (preserving all its 
+% peculiarities), and one which is a reimplementation from scratch. The 
+% default is to use the latter, but passing the \texttt{olddocinclude} 
+% option to \package{xdoc} selects the former.
+% 
+% 
+% \subsection{Old implementation}
+% 
+% It should be observed that this is not a complete implementation of the 
+% |\Doc|\-|Include| command---it only redefines the \package{ltxdoc} 
+% macros that need to be changed if the |\Doc|\-|Include| command is to 
+% work with \package{xdoc} (it doesn't for example change the definition 
+% of |\Doc|\-|Include| itself). Furthermore it doesn't define anything if 
+% the \package{ltxdoc} document class hasn't been loaded, since then the 
+% details of the definition of |\Doc|\-|Include| (even if it would be 
+% defined) are unknown.
+% 
+% \begin{macro}{\CodelineIndex}
+%   \changes{prot2.1}{2000/10/08}{Using \cs{thecodelineno}. (LH)}
+% \begin{macro}{\filesep}
+%   \changes{prot2.2}{2001/02/13}{Redefined to use 
+%      \cs{XD@page@compositor}. (LH)}
+% \begin{macro}{\@docinclude}
+%   \package{ltxdoc} redefines |\codeline@wrindex| so that |\filesep| is 
+%   prepended to each codeline number that is written to the index file. 
+%   That redefinition has no effect unless the |\Codeline|\-|Index| 
+%   command is executed afterwards however, so there is no harm in having 
+%   |\Codeline|\-|Index| itself apply the corresponding change.
+%    \begin{macrocode}
+%<*pkg>
+\@ifpackagewith{xdoc2}{olddocinclude}{%
+   \@ifclassloaded{ltxdoc}{%
+      \renewcommand\CodelineIndex{%
+         \makeindex
+         \let\XD@if@index=\@firstoftwo
+         \codeline@indextrue
+         \def\TheXDIndexNumber{\filesep\thecodelineno}%
+      }%
+%    \end{macrocode}
+%   The |\filesep| macro is redefined so that the \package{docindex} 
+%   package~\cite{docindex} can use a |page_compositor| string different 
+%   from the default |-| simply by redefining |\XD@page@compositor|. 
+%   This redefinition has to be put in |\docincludeaux| since that macro 
+%   redefines |\filesep| too.
+%    \begin{macrocode}
+      \expandafter\def \expandafter\docincludeaux \expandafter{%
+         \docincludeaux
+         \gdef\filesep{\thepart\XD@page@compositor}%
+      }
+%    \end{macrocode}
+%   The change to |\@docinclude| merely consists of inserting code for 
+%   writing an |External|\-|XRef|\-|Wrap| to the \texttt{.aux} file to 
+%   record the new value of the \texttt{part} counter.
+%    \begin{macrocode}
+      \def\@docinclude#1 {%
+         \clearpage
+         \if@filesw
+            \immediate\write\@mainaux{\string\@input{#1.aux}}%
+         \fi
+         \@tempswatrue
+         \if@partsw
+            \@tempswafalse
+            \edef\@tempb{#1}%
+            \@for\@tempa:=\@partlist\do{%
+               \ifx\@tempa\@tempb\@tempswatrue\fi
+            }%
+         \fi
+         \if@tempswa
+            \let\@auxout\@partaux
+            \if@filesw
+               \immediate\openout\@partaux #1.aux
+               \immediate\write\@partaux{\relax}%
+            \fi
+            \part{#1.dtx}%
+            \if@filesw
+               \immediate\write\@partaux{\@percentchar\@percentchar
+                  ExternalXRefWrap {\filesep} {}%
+               }%
+            \fi
+            {%
+               \let\ttfamily\relax
+               \xdef\filekey{%
+                  \filekey, \thepart={\ttfamily\currentfile}%
+               }%
+            }%
+            \DocInput{#1.dtx}%
+            \clearpage
+            \@writeckpt{#1}%
+            \if@filesw \immediate\closeout\@partaux \fi
+         \else
+            \@nameuse{cp@#1}%
+         \fi
+         \let\@auxout\@mainaux
+      }
+   }{}
+}{}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}
+% 
+% 
+% \subsection{New implementation}
+% \label{Ssec:New DocInclude}
+% 
+% The default action of the second implementation is to be precisely an 
+% |\include| variant of |\DocInput|, but in addition to that it also 
+% has a (one-argument) hook called |\docincludeaux| which is executed 
+% before a file is actually |\DocInput|ted, but after it has been 
+% determined that it should be included, and this hook is only executed 
+% for the files which should be |\include|d. This hook is normally 
+% |\@gobble|, but passing the \texttt{fileispart} option to 
+% \package{xdoc} redefines it to start a new part and set the pagestyle.
+% 
+% \begin{macro}{\DocInclude}
+% \begin{macro}{\@docinclude}
+%   Most of the code for the |\DocInclude| command is put in the 
+%   |\@docinclude| macro; |\DocInclude| simply checks that it hasn't 
+%   been nested. The main difference to |\include| is that a nested 
+%   |\DocInclude| becomes an error plus the corresponding |\DocInput|, 
+%   whereas a nested |\include| simply becomes an error. The rationale 
+%   for this is that it is probably closer to what was intended.
+%   
+%   The argument of |\@docinclude| is, oddly enough, space-delimited. 
+%   This is inherited from the |\@include| macro in the \LaTeX\ kernel, 
+%   where it is a hack to make sure that the part \texttt{.aux} file 
+%   that is opened for writing really gets the suffix \texttt{.aux} (in 
+%   the worst case, \TeX\ could start overwriting a \texttt{.tex} file 
+%   instead).
+%    \begin{macrocode}
+\@ifpackagewith{xdoc2}{olddocinclude}{}{%
+   \def\DocInclude#1{%
+      \ifnum\@auxout=\@partaux
+         \@latexerr{\string\include\space cannot be nested}{%
+            Your \protect\DocInclude\space will be reduced to a
+            \protect\DocInput.%
+         }%
+         \DocInput{#1.dtx}%
+      \else \@docinclude#1 \fi
+   }%
+%    \end{macrocode}
+%   The only things in this |\@docinclude| that are not precisely as in 
+%   |\@include| are the |\docincludeaux| and |\DocInput| commands.
+%    \begin{macrocode}
+   \def\@docinclude#1 {%
+      \clearpage
+      \if@filesw 
+         \immediate\write\@mainaux{\string\@input{#1.aux}}%
+      \fi
+      \@tempswatrue
+      \if@partsw 
+         \@tempswafalse
+         \edef\@tempb{#1}%
+         \@for\@tempa:=\@partlist\do{%
+            \ifx\@tempa\@tempb \@tempswatrue \fi
+         }%
+      \fi
+      \if@tempswa
+         \let\@auxout\@partaux
+         \if@filesw
+            \immediate\openout\@partaux #1.aux
+            \immediate\write\@partaux{\relax}%
+         \fi
+         \docincludeaux{#1.dtx}%
+         \DocInput{#1.dtx}%
+         \clearpage
+         \@writeckpt{#1}%
+         \if@filesw \immediate\closeout\@partaux \fi
+      \else
+         \deadcycles\z@
+         \@nameuse{cp@#1}%
+      \fi
+      \let\@auxout\@mainaux
+   }%
+}{}
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{option}{fileispart}
+%   \begin{macro}{\docincludeaux}
+%     The \texttt{fileispart} option works by (re)defining a couple of 
+%     macros, of which the |\doc|\-|include|\-|aux| macro is the most 
+%     important. Its syntax is
+%     \begin{quote}
+%       |\docincludeaux|\marg{filename}
+%     \end{quote}
+%     where \meta{filename} is the name of a file that will be inputted. 
+%     The \texttt{fileispart} definition of this is to set |\currentfile| 
+%     to the harmless character string of \meta{filename}, produce a 
+%     |\part| heading whose text is that \meta{filename}, add the 
+%     \meta{filename} to the |\filekey| macro, set the page style to 
+%     \texttt{docpart}, clear the |\filedate|, |\fileversion|, and 
+%     |\fileinfo| macros, and write an |External|\-|XRef|\-|Wrap| 
+%     XXR-command to the \texttt{.aux} file to record the new codeline 
+%     number prefix.
+%    \begin{macrocode}
+\@ifpackagewith{xdoc2}{olddocinclude}{\iffalse}{
+   \@ifpackagewith{xdoc2}{fileispart}{\iftrue}{
+      \let\docincludeaux=\@gobble
+      \iffalse
+   }
+} % If fileispart and not olddocinclude then
+   \def\docincludeaux#1{%
+      \MakeHarmless\currentfile{#1}%
+      \part{\texttt{\currentfile}}%
+      \pagestyle{docpart}%
+      \let\filedate\@empty
+      \let\fileversion\@empty
+      \let\fileinfo\@empty
+      \protected@xdef\filekey{%
+         \filekey, \thepart=\texttt{\currentfile}%
+      }%
+      \if@filesw
+         \immediate\write\@partaux{\@percentchar\@percentchar
+            ExternalXRefWrap {\thepart\XD@page@compositor} {}%
+         }%
+      \fi
+   }%
+%    \end{macrocode}
+%   \end{macro}
+%   
+%   \begin{macro}{\CodelineIndex}
+%     \changes{prot2.1}{2000/10/08}{Using \cs{thecodelineno}. (LH)}
+%     The \texttt{fileispart} option also adds the \texttt{codelineno} 
+%     counter to the reset list for \texttt{part} and changes the format 
+%     of codeline numbers written to the index.
+%    \begin{macrocode}
+   \@ifclassloaded{ltxdoc}{}{\@addtoreset{codelineno}{part}}%
+   \renewcommand\CodelineIndex{%
+      \makeindex
+      \let\XD@if@index=\@firstoftwo
+      \codeline@indextrue
+      \def\TheXDIndexNumber{\thepart\XD@page@compositor\thecodelineno}%
+   }%
+%    \end{macrocode}
+%   \end{macro}
+%   
+%   \begin{macro}{\partname}
+%   \begin{macro}{\thepart}
+%   \begin{macro}{\IndexParms}
+%     Finally there are a couple of macros which are redefined for 
+%     aesthetic rather than technical reasons. Passing the 
+%     \texttt{fileispart} option sets |\partname| to \texttt{File}, sets 
+%     |\thepart| to |\aalph{part}|, and adds a setting of pagestyle to 
+%     |\IndexParms|. (The pagestyle setting is added to 
+%     |\index@|\B|prologue| by \package{ltxdoc}, but I think 
+%     |\Index|\-|Parms| is more appropriate.)
+%    \begin{macrocode}
+   \def\partname{File}
+   \def\thepart{\aalph{part}}
+   \expandafter\def \expandafter\IndexParms
+      \expandafter{\IndexParms \pagestyle{docindex}}
+%    \end{macrocode}
+%   \end{macro}\end{macro}\end{macro}
+%   
+%   In case the index formatting is handled by the \package{docindex} 
+%   package~\cite{docindex} (or its \LaTeXe\ incarnation 
+%   \package{docidx2e}), the above addition to |\Index|\-|Parms| won't 
+%   have any effect. Therefore \package{xdoc} also passes the 
+%   \texttt{use}\-\texttt{doc}\-\texttt{index}\-\texttt{ps} option on 
+%   to these packages.
+%    \begin{macrocode}
+   \PassOptionsToPackage{usedocindexps}{docindex}
+   \PassOptionsToPackage{usedocindexps}{docidx2e}
+\fi
+%    \end{macrocode}
+% \end{option}
+% 
+% \begin{macro}{\ps@docpart}
+% \begin{macro}{\setfileinfo}
+% \begin{macro}{\XD@set@file@info}
+%   The \texttt{docpart} pagestyle is for pages made from the 
+%   |\DocInclude|d files. The page footers contain the page number, the 
+%   part (file) number, and the current file name. It also contains the 
+%   file date and version if that information is available.
+%   
+%   \package{ltxdoc} uses |\GetFileInfo| to get the date and version 
+%   information, but that's a very peculiar practice. The data one wants 
+%   to present are about the file being typeset---typically the version 
+%   of the package that is documented in this file---whereas the 
+%   |\GetFileInfo| command really extracts information about 
+%   \emph{unpacked} classes, packages, and similar files---files that 
+%   contribute to the typesetting by defining commands, not by containing 
+%   text. Such information may be of interest for documents which contain 
+%   alternative code for incompatible versions of for example a package, 
+%   but it is of no use for printing version information as above since 
+%   the version of a package used for typesetting a \texttt{.dtx} file 
+%   need not be the version actually contained in that \texttt{.dtx} 
+%   file. Thus the only way to make this work is by doing as the \LaTeX\ 
+%   kernel source and include |\ProvidesFile| commands for the 
+%   \texttt{.dtx} file in each such file, which is a rather peculiar use 
+%   of the |\ProvidesFile| command.
+%   
+%   The |\setfileinfo| command provides an equivalent feature in a less 
+%   roundabout way. It has the syntax
+%   \begin{quote}
+%     |\setfileinfo[|\meta{date}\verb*+ +\meta{version}\verb*+ +^^A
+%       \meta{info}|]|
+%   \end{quote}
+%   and it sets |\filedate| to \meta{date}, |\fileversion| to 
+%   \meta{version}, and |\fileinfo| to \meta{info} if the optional 
+%   argument is present; if the optional argument is missing or contains 
+%   fewer than three words then the missing fields are set to |?|.
+%   
+%    \begin{macrocode}
+\@ifpackagewith{xdoc2}{olddocinclude}{}{%
+   \def\ps@docpart{%
+      \def\@oddfoot{%
+         File: \texttt{\currentfile}%
+         \ifx \filedate\@empty \else \ Date: \filedate\fi
+         \ifx \fileversion\@empty \else \ Version: \fileversion\fi
+         \hfill\thepage
+      }%
+      \if@twoside
+         \def\@evenfoot{%
+            \thepage\hfill
+            File: \texttt{\currentfile}%
+            \ifx \filedate\@empty \else \ Date: \filedate\fi
+            \ifx \fileversion\@empty \else \ Version: \fileversion\fi
+         }%
+      \else \let\@evenfoot\@oddfoot \fi
+   }
+%    \end{macrocode}
+%   The corresponding definition in \package{ltxdoc} (there it appears in 
+%   |\docincludeaux|) is peculiar in that the odd page footer is set 
+%   globally but the even page footer only locally.
+%   
+%   The definition of |\setfileinfo| follows that of |\GetFileInfo| 
+%   except for the fact that the |\relax|es have been replaced by 
+%   |\@empty|s. 
+%    \begin{macrocode}
+   \newcommand\setfileinfo[1][]{%
+      \edef\@tempa{#1}%
+      \expandafter\XD@set@file@info \@tempa\@empty? ? \@empty\@empty
+   }
+   \def\XD@set@file@info#1 #2 #3\@empty#4\@empty{%
+      \def\filedate{#1}%
+      \def\fileversion{#2}%
+      \def\fileinfo{#3}%
+   }
+}{}
+%    \end{macrocode}
+%   The reason for making the argument of |\setfileinfo| optional is 
+%   that with the |\Provides|\-|File| practice one can (potentially) put 
+%   all date and version information in one place through tricks like
+%   \iffalse
+%<*example>
+% \fi
+%\begin{verbatim}
+%%    \begin{macrocode}
+%\ProvidesPackage{foobar}
+%%    \end{macrocode}
+%% \ProvidesFile{foobar.dtx}
+%    [2000/02/02 v1.0 Silly example package]
+%%
+%\end{verbatim}\iffalse
+%</example>
+% \fi
+%   By making the argument of |\setfileinfo| optional, I make sure that 
+%   people who have used such tricks only have to replace the 
+%   |\ProvidesFile{foobar.dtx}| by |\setfileinfo|.
+% \end{macro}\end{macro}\end{macro}
+% 
+% 
+% \begin{macro}{\ps@docindex}
+% \begin{macro}{\filekey}
+%   The \texttt{docindex} pagestyle is for the index in 
+%   \texttt{fileispart} documents. It prints a file key, which is a 
+%   list of all the included files and their corresponding part letters, 
+%   at the bottom of every page. The file key is stored in the macro 
+%   |\filekey|, which should have been constructed file by file as they 
+%   are included. To add a file to the file key, it is recommended that 
+%   you do
+%   \begin{quote}
+%     |\protected@xdef\filekey{\filekey, |\meta{entry for new file}|}|
+%   \end{quote}
+%   The \texttt{fileispart} version of |\docincludeaux| already does 
+%   this. The initial value of |\filekey| is |\@gobble| so that the 
+%   comma before the first entry is removed. The |\@empty| below is 
+%   there in case no entry has been inserted.
+%    \begin{macrocode}
+% \@ifpackagewith{xdoc2}{olddocinclude}{}{%
+   \def\ps@docindex{%
+      \def\@oddfoot{%
+         \parbox{\textwidth}{%
+            \strut\footnotesize\raggedright
+            \textbf{File Key:} \filekey\@empty
+         }%
+      }%
+      \let\@evenfoot\@oddfoot
+   }%
+   \let\filekey\@gobble
+% }
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% It should be observed that since |\ps@docindex| only sets the page 
+% style locally, the page style will revert to its previous setting at 
+% the end of the \texttt{theindex} environment. As that previous 
+% setting is probably that of the \texttt{docpart} page style, you 
+% might have to set the page style manually.
+% 
+% \begin{macro}{\aalph}
+% \begin{macro}{\@aalph}
+%   |\aalph| is a variant of |\alph| which continues with the upper case 
+%   letters for 27--52. It is defined by \package{ltxdoc}, so it is 
+%   merely provided here.
+%    \begin{macrocode}
+\providecommand*\aalph[1]{\@aalph{\csname c@#1\endcsname}}
+\providecommand*\@aalph[1]{%
+   \ifcase#1\or a\or b\or c\or d\or e\or f\or g\or h\or i\or
+          j\or k\or l\or m\or n\or o\or p\or q\or r\or s\or
+          t\or u\or v\or w\or x\or y\or z\or A\or B\or C\or
+          D\or E\or F\or G\or H\or I\or J\or K\or L\or M\or
+          N\or O\or P\or Q\or R\or S\or T\or U\or V\or W\or
+          X\or Y\or Z\else\@ctrerr\fi
+}
+%    \end{macrocode}
+%   In \texttt{source2e.tex} one can see that \package{doc}'s standard 
+%   \texttt{gind.ist} index style file won't sort the 35th file (part 
+%   \texttt{I}) correctly since it causes \package{makeindex} to read an 
+%   \texttt{I} as ``upper case Roman numeral one'', but I doubt very 
+%   many people encounter that problem in their projects.
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\XD@page@compositor}
+%   \changes{prot2.2}{2001/02/13}{Macro added, other macros changed to 
+%      use it. (LH)}
+%   The |\XD@page@compositor| macro contains the string which is put 
+%   between the parts of a composite number in the index; it 
+%   corresponds to the |page_compositor| parameter of 
+%   \package{makeindex}.
+%    \begin{macrocode}
+\providecommand*\XD@page@compositor{-}
+%    \end{macrocode}
+% \end{macro}
+% 
+%
+% 
+% \section{Miscellanea}
+% 
+% \subsection{Some \LaTeXplus\ stuff}
+% 
+% \begin{macro}{\BooleanFalse}
+% \begin{macro}{\BooleanTrue}
+% \begin{macro}{\NoValue}
+%   These three macros are borrowed from the \package{xparse} 
+%   package~\cite{xparse}, where they work as the three values 
+%   \emph{boolean false}, \emph{boolean true}, and \emph{absence of 
+%   value} respectively. The definitions are taken from  
+%   \package{xparse} v\,0.17 (1999/09/10).
+%    \begin{macrocode}
+\@ifundefined{BooleanFalse}{\def\BooleanFalse{TF}}{}
+\@ifundefined{BooleanTrue}{\def\BooleanTrue{TT}}{}
+\@ifundefined{NoValue}{\def\NoValue{-NoValue-}}{}
+%    \end{macrocode}
+%   By using these macros (rather than some homegrown set of macros 
+%   or tokens) for denoting these values here I hopefully simplify a 
+%   transition to \LaTeXplus, but I don't want to rely on \LaTeXplus\ 
+%   since it hasn't been released yet.
+% \end{macro}\end{macro}\end{macro}
+% 
+% 
+% \subsection{The \cs{meta} command}
+% 
+% A reimplementation which has already (as of v\,2.0k) found its way into 
+% the \package{doc} package is the one that the |\meta| command is made 
+% robust, but since some people might still have older 
+% versions of \package{doc} and since that feature is needed for 
+% |\describe|\-|cs|\-|family|, I apply it here too. First I check 
+% whether the definition of |\meta| is the old non-robust definition, 
+% and only apply the fix if it is. 
+%    \begin{macrocode}
+\begingroup
+\obeyspaces%
+\catcode`\^^M\active%
+\gdef\@gtempa{\begingroup\obeyspaces\catcode`\^^M\active%
+\let^^M\do@space\let \do@space%
+\def\-{\egroup\discretionary{-}{}{}\hbox\bgroup\itshape}%
+\m@ta}%
+\endgroup
+\ifx \meta\@gtempa
+%    \end{macrocode}
+% 
+% \begin{macro}{\l@nohyphenation}
+%   The new implementation needs a |\language| without any hyphenation 
+%   patterns. By switching to that language, one can inhibit 
+%   hyphenation in a piece of text regardless of what line-breaking 
+%   parameter settings are in force when the paragraph is actually 
+%   broken. This new language will be called \texttt{nohyphenation} and 
+%   it is only allocated if it isn't already known (since some 
+%   \package{babel} settings files already defines this |\language|).
+%    \begin{macrocode}
+   \@ifundefined{l@nohyphenation}{\newlanguage\l@nohyphenation}{}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\meta}
+% \begin{macro}{\meta@font@select}
+%   This is the definition of |\meta| from \package{doc} v\,2.0m. For 
+%   an explanation of the implementation, se a \texttt{doc.dtx} at least 
+%   that new or entry \texttt{latex/3170} in the \LaTeX\ bugs database.
+%    \begin{macrocode}
+   \DeclareRobustCommand\meta[1]{%
+      \ensuremath\langle
+      \ifmmode \expandafter \nfss@text \fi
+      {%
+         \meta@font@select
+         \edef\meta@hyphen@restore
+            {\hyphenchar\the\font\the\hyphenchar\font}%
+         \hyphenchar\font\m@ne
+         \language\l@nohyphenation
+         #1\/%
+         \meta@hyphen@restore
+      }\ensuremath\rangle
+   }
+%    \end{macrocode}
+%    \begin{macrocode}
+   \let\meta@font@select=\itshape
+\fi
+%    \end{macrocode}
+% \end{macro}\end{macro}
+% 
+% \begin{macro}{\MetaNormalfont}
+%   \changes{prot2}{2000/07/24}{Removed robustness; protected it 
+%      explicitly wherever needed instead. (LH)}
+%   The |\MetaNormalfont| command redefines |\meta@font@select| to do a 
+%   |\normal|\-|font| before the |\itshape|. It is useful if |\meta| is 
+%   going to be used to make |\rmfamily| interjections in |\ttfamily| 
+%   text.
+%    \begin{macrocode}
+\newcommand\MetaNormalfont{\def\meta@font@select{\normalfont\itshape}}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\XD@harmless\meta}
+%   This macro is needed for making |\meta| behave as described in the 
+%   argument of |\describe|\-|cs|\-|family|, i.e., in text which is 
+%   going to be converted into a harmless character string. 
+%    \begin{macrocode}
+\@namedef{XD@harmless\string\meta}#1{%
+   \toks@=\expandafter{\the\toks@ \meta{#1}}%
+   \XD@harmless@
+}
+%    \end{macrocode}
+% \end{macro}
+% 
+% 
+% \subsection{The checksum feature}
+% 
+% The checksum mechanism in \package{doc} is a remnant from the times 
+% when file truncation was a common problem and a mechanism for 
+% detecting this was a great help.\footnote{Even though I suspect that 
+% the recommended use of it---to put the checking \cs{Finale} at the 
+% end of the \texttt{.dtx} file---may have reduced its usefulness 
+% dramatically, as that \cs{Finale} would have been the one thing that 
+% surely disappears if the file is truncated.} Today its main usefulness 
+% seems to lie in that it distinguishes versions of a file that are 
+% ``being worked on'' (where the checksum probably doesn't match) from 
+% versions of a file that are ``polished and ready for upload'' 
+% (someone has bothered to fix the checksum), and as it exists it might 
+% as well stay. There is a problem however with files which do not 
+% contain \TeX\ code, as simply counting backslashes quite probably 
+% isn't a good (or even reasonable) way of forming a checksum for these 
+% files (if the checksum turns out to be zero, \package{doc} will 
+% complain no matter what you do).
+% 
+% \begin{macro}{\check@checksum}
+%   \changes{prot2.1}{2000/10/02}{Redefinition added. (LH)}
+%   For that reason, the |\check@checksum| macro is redefined to only 
+%   write the ``no checksum'' warning to the log file if the checksum 
+%   hasn't been set.
+%    \begin{macrocode}
+\renewcommand\check@checksum{%
+   \relax
+   \ifnum \check@sum=\z@
+      \PackageInfo{doc}{This macro file has no checksum!\MessageBreak
+         The checksum should be \the\bslash@cnt}%
+   \else\ifnum \check@sum=\bslash@cnt
+      \typeout{*******************}%
+      \typeout{* Checksum passed *}%
+      \typeout{*******************}%
+   \else
+      \PackageError{doc}{Checksum not passed (\the\check@sum
+         <>\the\bslash@cnt)}{The file currently documented seems 
+         to be wrong.\MessageBreak Try to get a correct version.}%
+   \fi\fi
+   \global\check@sum\z@
+}
+%    \end{macrocode}
+% \end{macro}
+%
+% 
+% \subsection{The \cs{theCodelineNo} situation}
+% \label{Ssec:CodelineNo}
+% 
+% \changes{prot2.1}{2000/10/08}{\cs{theCodelineNo} situation cleared 
+%    up. (LH)}
+% \package{doc} incorporates formatting of the value of the 
+% \texttt{CodelineNo} counter in the |\theCodelineNo| macro, which is a 
+% bit awkward since it prevents using this macro in making e.g.\ index 
+% entries. To get around this, \package{xdoc} introduces the alternative 
+% name \texttt{codelineno} for this counter so that |\thecodelineno| can 
+% produce the value representation without formatting.
+% 
+% \begin{macro}{\c@codelineno}
+% \begin{macro}{\cl@codelineno}
+% \begin{macro}{\p@codelineno}
+% \begin{macro}{\thecodelineno}
+%   The control sequences connected to the \texttt{codelineno} counter 
+%   are |\let| so that they refer to the same |\count| register as the 
+%   \texttt{CodelineNo} counter. Note that \texttt{CodelineNo} isn't a 
+%   proper \LaTeX\ counter, so the macros |\cl@CodelineNo| and 
+%   |\p@CodelineNo| are undefined. |\thecodelineno| is set to the default 
+%   value for a new counter.
+%    \begin{macrocode}
+\@ifundefined{c@codelineno}{}{%
+   \PackageInfo{xdoc2}{Overwriting codelineno counter}%
+}
+\let\c@codelineno=\c@CodelineNo
+\let\cl@codelineno=\@empty
+\let\p@codelineno=\@empty
+\def\thecodelineno{\@arabic\c@codelineno}
+%    \end{macrocode}
+% \end{macro}\end{macro}\end{macro}\end{macro}
+% 
+% \begin{macro}{\PrintCodelineNo}
+%   The |\PrintCodelineNo| command is the new recommended command for 
+%   printing the formatted form of the codeline number counter. People 
+%   who write their own \texttt{macrocode}-like environments should use 
+%   |\PrintCodelineNo| instead of \package{doc}'s |\theCodelineNo|.
+%    \begin{macrocode}
+\newcommand\PrintCodelineNo{\reset@font\scriptsize\thecodelineno}
+%    \end{macrocode}
+% \end{macro}
+% 
+% \begin{macro}{\theCodelineNo}
+%   Finally |\theCodelineNo| is redefined to reference 
+%   |\PrintCodelineNo|. This is done for the sake of backwards 
+%   compability; I didn't feel like redefining |\macro@code| just for 
+%   the sake of changing the |\theCodelineNo| into a |\PrintCodelineNo|).
+%    \begin{macrocode}
+\def\theCodelineNo{\PrintCodelineNo}
+%    \end{macrocode}
+% \end{macro}
+% 
+%    \begin{macrocode}
+%</pkg>
+%    \end{macrocode}
+% 
+% 
+% \section{Problems and things to do}
+% 
+% This section lists some problems that exist with the current 
+% implementations of commands in \package{xdoc}. The list is rather 
+% unstable---items are added as I realize there is a problem and removed 
+% when I find a solution---an in parts it is rather esoteric since most 
+% of the problems have only been found theoretically.
+% 
+% \medskip
+% 
+% One of the less well-known features of the |\verb| command is that 
+% it automatically inhibits the known syntactic ligatures. There is 
+% no such mechanism implemented for the harmless character strings, 
+% so some (in \TeX\ \texttt{macrocode} uncommon) character sequences 
+% (such as |!`|) may produce unwanted results. The quick hack to 
+% circumvent this is to use the |\SetHarmState| command to mark one 
+% of the characters involved as problematic, as the |\PrintChar| 
+% command is implemented so that the character it prints will not be 
+% involved in ligaturing or kerning. On the other hand, \package{doc} 
+% does nothing to suppress syntactic ligatures in macro or environment 
+% names when they are printed in the margin, so for that material the 
+% \package{xdoc} implementation might actually improve things, although 
+% it could perform worse for verbatim material in the index and list of 
+% changes.
+% 
+% \medskip
+% 
+% Things to do and\slash or think about:
+% \begin{itemize}
+%   \item
+%     Examine how complicated it would be to convert the 
+%     |\PrintChar| commands for visible characters in a harmless 
+%     character string back to explicit characters, for possible use in 
+%     sort keys. (This could be used to ensure that visible characters 
+%     are sorted in strict ASCII order.)
+%   \item
+%     Should those ``letters'' which are commonly used as word 
+%     separators---in \LaTeX\ code mainly |@|---be ignored when sort 
+%     keys are being formed (just like the backslash is)? (This would 
+%     require a change in the implementation of the \texttt{macro} 
+%     environment.)
+%     
+%     A mechanism for doing this is included as of prototype version~2.1.
+%   \item
+%     Examine how much more efficient it would be to put temporary 
+%     additions to the index exclude list in a separate list instead of 
+%     the main list. This could be advantageous for deeply nested 
+%     \texttt{macro} environments, as \TeX\ will otherwise store as many 
+%     (almost identical and often rather long) copies of the exclude list 
+%     as there are nested environments.
+%     
+%     When asked about it, Frank Mittelbach didn't think there was 
+%     any gains worth mentioning in this. On the other hand it might be 
+%     worth investigating reimplementations that avoid calling |\trivlist| 
+%     at the beginning of each \texttt{macro}-like environment when they 
+%     are nested, since |\trivlist| does quite a lot of assignments.
+%   
+%   \item
+%     In an automatically generated index one often faces the problem 
+%     that the entries at the innermost level are best formatted in one 
+%     way when there is only one, but in a completely different way when 
+%     there are several of them. To get optimal formatting in both cases, 
+%     one would like to let the |\item|, |\subitem|, |\subsubitem| or 
+%     corresponding macros detect the situation in this respect and 
+%     choose the optimal formatting at each case.
+%     
+%     A mechanism for this is implemented by the \package{docindex} 
+%     package.
+% \end{itemize}
+% 
+% 
+% \begin{thebibliography}{9}
+%   \bibitem{ltxdoc}
+%     David Carlisle: 
+%     \textit{The file \texttt{ltxdoc.dtx} for use with \LaTeXe},
+%     The \LaTeX3 Project; ^^A , 1993~ff.
+%     \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash 
+%     \texttt{latex}\slash \texttt{base}\slash \texttt{ltxdoc.dtx}.
+%   \bibitem{docindex}
+%     Lars Hellstr\"om:
+%     \textit{The \package{docindex} package}, 2001,
+%     \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash 
+%     \texttt{latex}\slash \texttt{exptl}\slash \texttt{xdoc}\slash
+%     \texttt{docindex.dtx}.
+%   \bibitem{fontinst}
+%     Alan Jeffrey, Sebastian Rahtz, Ulrik Vieth (and as of v\,1.9 Lars 
+%     Hellstr\"om): \textit{The \package{fontinst} utility}, v\,1.8~ff., 
+%     documented source code, 
+%     \textsc{ctan}:\discretionary{}{}{\thinspace}^^A
+%     \texttt{fonts}\slash \texttt{utilities}\slash 
+%     \texttt{fontinst}\slash \texttt{source}/
+%   \bibitem{clsguide}
+%     The \LaTeX3 Project: 
+%     \textit{\LaTeXe~for class and package writers}, 
+%     The \LaTeX3 Project; ^^A , 1995~ff.
+%     \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash 
+%     \texttt{latex}\slash \texttt{base}\slash \texttt{clsguide.tex}.
+%   \bibitem{doc}
+%     Frank Mittelbach, B.~Hamilton Kelly, Andrew Mills, Dave Love, and 
+%     Joachim \mbox{Schrod}: \textit{The \package{doc} and 
+%     \package{shortvrb} Packages}, The \LaTeX3 Project; ^^A , 1993~ff. 
+%     \textsc{ctan}:\discretionary{}{}{\thinspace}\texttt{macros}\slash 
+%     \texttt{latex}\slash \texttt{base}\slash \texttt{doc.dtx}.
+%   \bibitem{xparse}
+%     Frank Mittelbach, Chris Rowley, and David Carlisle: \textit{The 
+%     \package{xparse} package}, The \LaTeX3 Project, 1999. Currently 
+%     not available by anonymous FTP, but available by HTTP from 
+%     \texttt{www.latex-project.org} (look for ``experimental code'').
+% \end{thebibliography}
+% 
+% \Finale
+\endinput
\ No newline at end of file
diff --git a/Master/texmf-dist/source/latex/xdoc/xdoc2.ins b/Master/texmf-dist/source/latex/xdoc/xdoc2.ins
new file mode 100644
index 00000000000..ff4eb64bc5a
--- /dev/null
+++ b/Master/texmf-dist/source/latex/xdoc/xdoc2.ins
@@ -0,0 +1,37 @@
+% This file is the docstrip installation script for the xdoc2 package.
+% 
+% It may be distributed under the conditions of the LaTeX 
+% Project Public License, either version 1.2 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 1.2 or later is part of all distributions of LaTeX 
+% version 1999/12/01 or later.
+% 
+% Copyright 2000 2001 Lars Hellstr\"om
+
+\input docstrip
+
+\keepsilent
+
+\preamble
+
+This file may be distributed and/or modified under the conditions 
+of the LaTeX Project Public License, either version 1.2 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 1.2 or later is part of all distributions of LaTeX 
+version 1999/12/01 or later.
+
+This file may only be distributed together with a copy of the source 
+file from which it was generated. You may distribute that source file 
+without this generated file.
+
+\endpreamble
+
+\usedir{tex/latex/misc}
+\generate{\file{xdoc2.sty}{\from{xdoc2.dtx}{pkg,xdoc2}}}
+
+\endbatchfile
+\end