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+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \iffalse %%%%
+% %
+% Copyright (c) 2014 - Michiel Helvensteijn (www.mhelvens.net) %
+% %
+% https://github.com/mhelvens/latex-pkgloader %
+% %
+% This work may be distributed and/or modified under the conditions %
+% of the LaTeX Project Public License, either version 1.3 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 1.3 or later is part of all distributions of LaTeX %
+% version 2005/12/01 or later. %
+% %
+% This work has the LPPL maintenance status `maintained'. %
+% %
+% The Current Maintainer of this work is Michiel Helvensteijn. %
+% %
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% \fi %%%%
+
+\documentclass[a4paper]{pkgloader-packagedoc}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% Setup %
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\def\nt#1{\ensuremath{\hbox{\footnotesize$\langle$}\mathit{#1}\hbox{\footnotesize$\rangle$}}}
+\def\|{\ \mid\ }
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+% Global Changes %
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\changes{0.1.0}{2014/01/29}
+ {initial version}
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\begin{document} %
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+
+\maketitle
+
+\section {Introduction} % % % % % % % % % % % % % % % % % % % % % % % % % % % %
+
+\LaTeX\ can be extended by loading packages
+using a \lstinline+\usepackage+, \lstinline+\RequirePackage+ or \lstinline+\RequirePackageWithOptions+ command.
+Packages can add definitions, change existing ones, or otherwise extend functionality of the language.
+
+While the Turing-complete power of the \TeX\ family is quite useful at times, it does
+make it all too easy for independent package authors to step on each others
+toes. CTAN is full of conceptually independent packages that cannot be
+loaded together, or break if they are not loaded in a specific order.
+
+Yet, until now, there has been no automated package management to speak of.
+Document authors are usually told to avoid certain package combinations,
+or to load packages in some specific order.
+Occasionally, package authors patch their code to be aware of specific
+other packages, circumventing known conflicts.
+But this makes maintenance more difficult, because these package authors
+are `mixing concerns'; they put code related to other packages into their
+own package. And it is all done in an ad-hoc fashion.
+
+Enter \lstinline+pkgloader+.
+
+
+
+\subsection {Package Description} % % % % % % % % % % % % % % % % % % % % % %
+
+Here is an example of main file for a \LaTeX\ document
+which uses \lstinline+pkgloader+:
+
+\begin{latex}
+\documentclass{article}
+
+\RequirePackage{pkgloader}
+ \usepackage{xltxtra}
+ \usepackage[xetex]{graphicx}
+ $\smash{\raisebox{-1pt}{\small\vdots}}$
+\LoadPackagesNow
+
+\begin{document} $\ldots$ \end{document}
+\end{latex}
+
+The idea is to load \lstinline+pkgloader+ before loading any other package.
+It can then intercept all package loading requests, analyze them
+and load them properly, taking this burden off the shoulders of
+the average document author.
+
+Between the second and sixth lines, the loading of all packages
+is postponed. The \lstinline+\LoadPackagesNow+ command then
+loads the packages in some valid order. During this process,
+`conflict resolving' code may also be run, meant specifically to make
+other packages work together properly. If the above code were
+compiled without \lstinline+pkgloader+ (using the \XeTeX\ engine, as of this writing),
+the given order between \lstinline+xltxtra+ and \lstinline+graphicx+ would
+cause an error.
+%%
+The main advantage to this approach is that the complexity of dealing
+with package conflicts is moved to the \lstinline+pkgloader+ package and handled
+in a systematic manner.
+
+If you are a document author, this may be all you need to know to use
+\lstinline+pkgloader+. If you are interested in more advanced functionality,
+read on!
+
+
+\subsection {The \texttt{pkgloader} Area} % % % % % % % %
+
+\describeanymacro
+ {\ttfamily\bfseries\textbackslash RequirePackage\!\!\!\!\!}
+ {{\ttfamily{\bfseries\{}pkgloader{\bfseries\}}\quad\ldots\quad{\bfseries\textbackslash LoadPackagesNow}}}
+
+The \lstinline+pkgloader+ area is the area between
+\lstinline+\RequirePackage{pkgloader}+ and
+\lstinline+\LoadPackagesNow+.
+Within it, the three traditional package-loading commands
+are `hijacked', recording information rather than loading
+packages directly. Also, a \lstinline+\Load+ command is
+available, which offers more flexibility in regulating
+package loading behavior.
+
+|pkgloader| accepts sets of rules coming from outside
+packages, though support is still somewhat limited.
+Any |pkgloader-|\nt{something}|.sty| file can be loaded
+within the |pkgloader| area by passing \nt{something}
+as a package option. The file |pkgloader-recommended.sty|
+is loaded this way by default. You can overwrite this by
+passing |recommended=false| as an option. For example:
+
+\begin{latex}
+\RequirePackage[recommended=false, my-better-rules]{pkgloader}
+ $\smash{\raisebox{-1pt}{\small\vdots}}$
+\LoadPackagesNow
+\end{latex}
+
+This area does not play by the recommended package loading
+rules, but uses the rules in |pkgloader-my-better-rules.sty|
+instead.
+
+
+
+\subsection {Package Loading Requests} % % % % % % % %
+
+
+\marginnote{\ttfamily\bfseries\textbackslash usepackage\\
+ \textbackslash RequirePackage\\
+ \textbackslash RequirePackageW{\ldots}s}\noindent
+For requesting specific packages inside the |pkgloader| area,
+just use the three commands always used
+for this purpose: \lstinline+\usepackage+, \lstinline+\RequirePackage+ and
+\lstinline+\RequirePackageWithOptions+. Their syntax and effective semantics
+are the same as they have always been. Their effects are just delayed,
+reordered and perhaps modified by the active rules.
+
+
+
+\subsection {Package Loading Rules} % % % % % % % %
+
+\marginnote{\ttfamily\bfseries\textbackslash Load}\noindent
+Each invocation if the \lstinline+\Load+ command sets up a rule about
+a package or packages, which are not necessarily ever loaded.
+These rules can come from any number of different sources.
+A central registry will be maintained together with \lstinline+pkgloader+ itself
+in the form of |pkgloader-recommended.sty|,
+specifying well-known conflicts and resolutions.
+Individual package authors, however, can supply their own rules,
+as can document authors. Though ideally, for the
+average document author, things should `just work'.
+
+The \lstinline+\Load+ command expects the following syntax:
+
+\vskip\abovedisplayskip
+\begingroup
+\centering
+\begin{tabular}{r@{\ \ \ \ }r@{\ \ \ \ }l}
+ \nt{load} &$::=$& \lstinline+\Load+$\ \nt{package}\ \ \nt{clause}_1\ \ldots\ \nt{clause}_i$ \\
+ &$ \|$& \lstinline+\Load error+ $\ \ \ \,\nt{clause}_1\ \ldots\ \nt{clause}_i$ \\[2mm]
+
+ \nt{package} &$::=$& \lstinline+[+$\;\nt{options}\;$\lstinline+] {+$\;\nt{pkg}\;$\lstinline+} [+$\;\nt{version}\;$\lstinline+]+ \\[2mm]
+
+ \nt{clause} &$::=$& $\nt{order}\ \ \|\ \ \nt{condition}\ \ \|\ \ \nt{reason}$ \\[2mm]
+
+ \nt{order} &$::=$& \lstinline+before {+ $\nt{pkg}_1\,$\lstinline+, +$\ldots\,$\lstinline+, +$\nt{pkg}_j$ \lstinline+}+ \\
+ &$ \|$& \lstinline+after {+ $\nt{pkg}_1\,$\lstinline+, +$\ldots\,$\lstinline+, +$\nt{pkg}_j$ \lstinline+}+ \\
+ &$ \|$& \lstinline+early+ \\
+ &$ \|$& \lstinline+late+ \\[2mm]
+
+ \nt{condition} &$::=$& \lstinline+always+ $\ \ \|\ \ $
+ \lstinline+if loaded+ $\ \ \|\ \ $
+ \lstinline+if {+ $\nt{\phi}$ \lstinline+}+ \\[2mm]
+
+ \nt{\phi} &$::=$& $\nt{pkg}$ $\ \ \|\ \ $
+ $\nt{\phi}\ $\lstinline+&&+$\ \nt{\phi}$ $\ \ \|\ \ $
+ $\nt{\phi}\ $\lstinline+||+$\ \nt{\phi}$ $\ \ \|\ \ $
+ \lstinline+!+$\;\nt{\phi}$ $\ \ \|\ \ $
+ \lstinline+(+$\;\nt{\phi}\;$\lstinline+)+ \\[2mm]
+
+ \nt{reason} &$::=$& \lstinline+because {+ $\nt{token{-}list}$ \lstinline+}+
+\end{tabular}
+\endgroup
+\vskip\belowdisplayskip
+
+\noindent
+\nt{pkg} represents a package name.
+\nt{token{-}list} should expand to a human-readable text without formatting.
+
+\marginnote{\ttfamily\bfseries if}\noindent
+The \( \nt{condition} \) clause determines under which package loading
+conditions any and all parts of a rule are invoked.
+Here is an example of the use of the \( \nt{condition} \) clause:
+\begin{latex}
+\Load {res-ie-lst} if {inputenc && listings}
+\Load {fixltx2e} always
+\end{latex}
+
+\lstinline+res-ie-lst+ (a fictional package built specifically to resolve the
+conflict between \lstinline+inputenc+ and \lstinline+listings+) will be loaded if requested
+specifically, or if both \lstinline+inputenc+ and \lstinline+listings+ are loaded. The \lstinline+fixltx2e+ package is
+always loaded, as it was created to smooth over some mistakes in the
+\LaTeXe\ core.
+
+\marginnote{\ttfamily\bfseries always\\ if loaded}
+The \lstinline+always+ keyword makes a rule unconditional. The \lstinline+if loaded+
+directive makes a rule conditional on its package already being loaded anyway.
+This can be used to order two packages only when they are being loaded by other
+means, and is actually the default behavior (in other words, \lstinline+if loaded+
+really does nothing).
+
+\marginnote{\ttfamily\bfseries before\\ after}
+The \lstinline+before+ and \lstinline+after+ keywords should be pretty straightforward. They
+can be used for things like:
+\begin{latex}
+\Load {xltxtra} after {graphicx}
+\end{latex}
+which fixes the loading order between these two packages when they are both loaded.
+
+\marginnote{\ttfamily\bfseries early\\ late}
+But the set of \LaTeX\ packages is constantly growing, and it appears that
+some big packages should almost always be loaded early in the process,
+and others should almost always be loaded late. Therefore the \lstinline+early+
+and \lstinline+late+ stages are provided as a fallback mechanism. If two packages
+are not related by an explicit application order, their loading order
+may still be decided by their relative stages: \lstinline+early+ before `normal' before \lstinline+late+.
+That way, conflicts may be avoided in a majority of cases.
+This is implemented with |pkgloader-early| and |pkgloader-late| stubs in
+the loading order graph.
+
+The following example uses the \( \nt{order} \) clause
+in addition to the \( \nt{condition} \) clause:
+\begin{latex}
+\Load {res-ie-lst} if {inputenc && listings}
+ after {inputenc , listings}
+\Load {fixltx2e} always early
+\end{latex}
+An important observation about the loading order is that it
+might form a cycle when contradictory ordering rules are specified:
+\begin{latex}
+\Load {pkg1} after {pkg2}
+\Load {pkg2} after {pkg1}
+\end{latex}
+In practice this could happen if the authors of \lstinline+pkg1+ and \lstinline+pkg2+
+independently discover a conflict, and both try to solve it by patching
+their code and having their own package be loaded last. \lstinline+pkgloader+
+can provide a clear error message when this happens, allowing the
+two package authors to seek contact and collaborate on a solution.
+
+\marginnote{\ttfamily\bfseries error}
+Now, about the \lstinline+error+ keyword.
+Initially all package combinations are valid. But if two packages
+are irredeemably incompatible, their combination can be made to trigger
+an error message by a command such as the following:
+\begin{latex}
+\Load error if {algorithms && pseudocode}
+\end{latex}
+These two packages provide almost identical functionality and conflict
+on many command-names. It was generally agreed upon that they should
+never be loaded together. Document authors should simply choose one
+or the other.
+
+\marginnote{\ttfamily\bfseries because}
+Finally, the \( \nt{reason} \) clause can be used to supply a
+human-readable explanation of a rule.
+We finish the above examples by providing reasons:
+\begin{latex}[basewidth=.598em]
+\Load {res-ie-lst} if {inputenc && listings}
+ after {inputenc , listings}
+ because {it allows the use of 1 byte unicode
+ characters in code listings}
+
+\Load {fixltx2e} always early
+ because {it fixes some imperfections in LaTeX2e}
+
+\Load error when {algorithms && pseudocode}
+ because {they provide almost identical functionality
+ and conflict on many command names}
+\end{latex}
+In the future, reasons will be extracted automatically to
+generate documentation. For now, they are displayed with error
+messages related to the rule in question.
+
+
+\subsection {Status} % % % % % % % %
+
+So far, \lstinline+pkgloader+ seems to work as expected, but has not
+yet been tested as extensively as it should be. Therefore, bug-reports
+on the |pkgloader| issue tracker on Github would be most welcome.
+Also, lots more recommended package loading rules are needed.
+
+I nonetheless decided to publish the package now, because I've been
+promising to do so for a while now:
+
+\begin{center}
+ \url{http://tex.stackexchange.com/questions/123174}
+\end{center}
+
+\noindent
+I hope that, with feedback and community collaboration,
+use of this package will become widespread and package
+authors will be able to work in a more modular fashion.
+
+\emph{Future versions} of |pkgloader| will be able to deal with
+document classes, to intelligently merge package options
+and to track packages loaded by other packages in order
+to better inform the user --- perhaps even fix problems
+by carrying information into the next run through auxiliary files.
+But most of this will depend on feedback.
+
+
+
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+\end{document} %
+%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%