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% Chapter about scrlfile of the KOMA-Script guide
% Maintained by Markus Kohm
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% Kapitel über scrlfile in der KOMA-Script-Anleitung
% Verwaltet von Markus Kohm
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\ProvidesFile{scrlfile.tex}[2005/11/27 KOMA-Script guide (chapter: scrlfile)]
% Date of translated german file: 2005/08/10

\chapter{Control Package Dependencies with \Package{scrlfile}}
\labelbase{scrlfile}

\BeginIndex{Package}{scrlfile}

\begin{Explain}
  The introduction of \LaTeXe{} in 1994 brought many changes in the handling
  with \LaTeX-extensions.  Today the package author has many macros in order
  to determine if another package or class is employed and whether specific
  options are used.  The author can load other packages or can specify options
  in the the case the package is loaded later.  This has led to the
  expectation that the order of package-loading will be not important.  But
  this hope has not been fulfilled.
\end{Explain}

\section{About Package Dependencies}
\label{sec:scrlfile.dependency}
\begin{Explain}
  Often different packages define or redefine one macro again and again.  In
  such a case the order of package-loading becomes very important.  For the
  user this is sometimes difficult to understand the behaviour and in some
  cases the user wants only react on the loading of a package. This is also
  not really simple.

  Assuming the simple example that loads the package \Package{longtable} with
  a \KOMAScript{} document-class employed.  The \Package{longtable} package
  defines table captions suitable for the standard classes, but the captions
  are totally unsuitable for documents using \KOMAScript{} and thus the
  provided configuration commands have no influence.  In order to solve this
  problem the commands which are responsible for the table captions of the
  \Package{longtable} package have to be re-defined. But at the moment when
  the \Package{longtable} is loaded the \KOMAScript{} class is already
  processed.

  The only chance for \KOMAScript{} was to delay the re-definition until the
  begin of the document with help of the macro \Macro{AtBeginDocument}.  If
  the user wants to change the definitions too, it is recommended to do this
  in the preamble of the document.  But this is impossible since later at
  \Macro{begin}\PParameter{document} \KOMAScript will again overwrite the
  user-definition with its own.  Therefore the user has to delay his
  definition with \Macro{AtBeginDocument} as well.
  
  However, \KOMAScript{} shouldn't delay the re-definition until
  \Macro{begin}\PParameter{document}.  It would be enough to delay until the
  package \Package{longtable} has been loaded. But unfortunately the basic
  \LaTeX{} does not define appropriate commands. The package
  \Package{scrlfile} provides redress here.
  
  Likewise, it might be conceivable that before a package is loaded one would
  like to save the definition of a macro in a help-macro, in order to restore
  its meaning after the package has been loaded. The package
  \Package{scrlfile} allows this too.
  
  The employment of \Package{scrlfile} is not limited to package dependencies
  only.  Even dependencies with any other file can be attended.  For example
  the user can be warned if the not uncritical file \File{french.ldf} has been
  loaded.
  
  Though the package is particularly interesting for package authors, there
  are of course applications for normal \LaTeX{} users too.  Therefore this
  chapter gives and explains examples for both groups of users.
\end{Explain}


\section{Actions Prior and After Loading}
\label{sec:scrlfile.macros}

\begin{Declaration}
  \Macro{BeforeFile}\Parameter{file}\Parameter{instructions}\\
  \Macro{AfterFile}\Parameter{file}\Parameter{instructions}
\end{Declaration}%
\BeginIndex{Cmd}{BeforeFile}%
\BeginIndex{Cmd}{AfterFile}%
The macro \Macro{BeforeFile} enables to execute \PName{instructions}
the next time the \PName{file} is loaded.
In the same way works \Macro{AfterFile}, but here the
\PName{instructions} will be executed after the \PName{file}
has been loaded.
If \PName{file} will never be loaded then the \PName{instructions}
will never be executed.

\begin{Explain}
  In order to implement those features \Package{scrlfile}
  re-defines the well known \LaTeX{} command
  \Macro{InputIfFileExists}.
  If this macro has not the expected definition \Package{scrlfile}
  gives a warning.
  This is for the case that in future \LaTeX{} versions
  the macro can have a different definition or an other package
  has already re-defined it.
  
  The command \Macro{InputIfFileExists} is used 
  everytime \LaTeX{} has to load a file.
  This is independent from whether the actual command was \Macro{LoadClass},
  \Macro{documentclass}, \Macro{usepackage}, \Macro{RequiresPackage},
  or \Macro{include}. Exclusively the command
\begin{lstlisting}
  \input foo
\end{lstlisting}
  loads the file \texttt{foo} without to utilize
  \Macro{InputIfFileExists}. Therefore one should always use
\begin{lstlisting}
  \input{foo}
\end{lstlisting}
  instead. Notice the parentheses surrounding the file name!
\end{Explain}
%
\EndIndex{Cmd}{BeforeFile}%
\EndIndex{Cmd}{AfterFile}%

\begin{Declaration}
  \Macro{BeforeClass}\Parameter{class}\Parameter{instructions}\\
  \Macro{BeforePackage}\Parameter{package}\Parameter{instructions}
\end{Declaration}%
\BeginIndex{Cmd}{BeforeClass}%
\BeginIndex{Cmd}{BeforePackage}%
These both commands work the same way as \Macro{BeforeFile}.
The only difference is that the document class \PName{class}
and the \LaTeX{} package \PName{package} are specified
with their names and not with their file names.
That means the file extensions \File{.cls} and \File{.sty}
can be omitted.
%
\EndIndex{Cmd}{BeforeClass}%
\EndIndex{Cmd}{BeforePackage}%

\begin{Declaration}
  \Macro{AfterClass}\Parameter{class}\Parameter{instructions}\\
  \Macro{AfterClass*}\Parameter{class}\Parameter{instructions}\\
  \Macro{AfterPackage}\Parameter{package}\Parameter{instructions}\\
  \Macro{AfterPackage*}\Parameter{package}\Parameter{instructions}
\end{Declaration}%
\BeginIndex{Cmd}{AfterClass}%
\BeginIndex{Cmd}{AfterClass*}%
\BeginIndex{Cmd}{AfterPackage}%
\BeginIndex{Cmd}{AfterPackage*}%
The commands \Macro{AfterClass} und \Macro{AfterPackage} 
work the same way as \Macro{AfterFile}.
The only difference is that the document class \PName{class}
and the \LaTeX{} package \PName{package} are specified
with their names and not with their file names.
That means the file extensions \File{.cls} and \File{.sty}
can be omitted.
The starred versions execute the \PName{instructions} not
only next time the class or package is loaded, but also
immediately if the class or package has been loaded already.
%
\EndIndex{Cmd}{AfterClass}%
\EndIndex{Cmd}{AfterClass*}%
\EndIndex{Cmd}{AfterPackage}%
\EndIndex{Cmd}{AfterPackage*}%

\begin{Example}
  In the following an example for class and package authors
  shall be given.
  It shows how \KOMAScript{} itself employs the new commands.
  The class \Class{scrbook} contains:
\begin{lstlisting}
\AfterPackage{hyperref}{%
  \@ifpackagelater{hyperref}{2001/02/19}{}{%
    \ClassWarningNoLine{scrbook}{%
      You are using an old version of hyperref package!%
      \MessageBreak%
      This version has a buggy hack at many drivers%
      \MessageBreak%
      causing \string\addchap\space to behave strange.%
      \MessageBreak%
      Please update hyperref to at least version
      6.71b}}}
\end{lstlisting}
  Old versions of the \Package{hyperref} package re-define
  a macro of the \Class{scrbook} class in a way that does not
  work with newer \KOMAScript{} versions.
  New versions of \Package{hyperref} neglect these changes
  if a new \KOMAScript{} version is detected.
  For the case that \Package{hyperref} is loaded the code
  in \Class{scrbook} verifies that a appropriate
  \Package{hyperref} version is used.   If not the command gives
  a warning.

  At other places in three \KOMAScript{} classes following can be found:
\begin{lstlisting}
  \AfterPackage{caption2}{%
    \renewcommand*{\setcapindent}{%
\end{lstlisting}
  Next the package \Package{caption2} has been loaded, and only
  if the package has been loaded really, \KOMAScript{} re-defines
  its own command \Macro{setcapindent}.
  The exact code of the definition is not important.
  It should only be noted that \Package{caption2} claims the
  control over the \Macro{caption} macro.
  Thus the normal definition of the \Macro{setcapindent} macro
  would not work as expected.
  The re-definition improves the collaboration with \Package{caption2}.

  There are of course useful examples for normal \LaTeX{} user too.
  Suppose a document that should be availbale as PS file, using
  LaTeX{} and dvips, and as PDF file, using pdf\LaTeX.
  The document should contain hyper-links.
  In the List of Tables there are entries longer than one line.
  This is not a problem for the pdf\LaTeX{} way, since here
  hyper-links can run across multiple lines.  
  But if a \Package{hyperref} driver for dvips or
  hyper\TeX{} is used then this is not possible.
  In this case one wants that for the \Package{hyperref} setup
  the \Option{linktocpage} is used.
  
  The decision what \Package{hyperref} driver has to be used
  happens automatically via \File{hyperref.cfg}.
  The file has for example the content below.
\begin{lstlisting}
  \ProvidesFile{hyperref.cfg}
  \@ifundefined{pdfoutput}{\ExecuteOptions{dvips}}
                          {\ExecuteOptions{pdftex}}
  \endinput
\end{lstlisting}

  All following is now the task of \Macro{AfterFile}.
\begin{lstlisting}
  \documentclass{article}
  \usepackage{scrlfile}
  \AfterFile{hdvips.def}{\hypersetup{linktocpage}}
  \AfterFile{hypertex.def}{\hypersetup{linktocpage}}
  \usepackage{hyperref}
  \begin{document}
  \listoffigures
  \clearpage
  \begin{figure}
    \caption{This is an example for a long figure caption,
      but even though it does not employ the optional
         caption argument that would allow to write
         a short caption in the List of Figures.}
  \end{figure}
  \end{document}
\end{lstlisting}
  If now \Package{hyperref} drivers \Option{hypertex} or
  \Option{dvips} are used then the useful \Package{hyperref} option
  \Option{linktocpage} will be set.
  In the pdf\LaTeX{} case the option will not be set, since
  in that case an other \Package{hyperref} driver \File{hpdftex.def}
  will be used. That means neither \File{hdvips.def} nor
  \File{hypertex.def} will be loaded.
\end{Example}

\begin{Explain}
  Furthermore the loading of package \Package{scrlfile}
  and the \Macro{AfterFile} statement can be written
  in the private \File{hyperref.cfg}.
  But then instead of \Macro{usepackage} the macro
  \Macro{RequiresPackage} ought be used, see \cite{latex:clsguide}.
  The new lines have to be inserted directly after 
  \Macro{ProvidesFile} line, thus prior to the execution
  of the options \Option{dvips} or \Option{pdftex}.
\end{Explain}%
\EndIndex{Package}{scrlfile}

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