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% Chapter about scrlfile of the KOMA-Script guide
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\ProvidesFile{scrlfile.tex}[2007/09/26 KOMA-Script guide (chapter: scrlfile)]
\translator{Gernot Hassenpflug\and Markus Kohm}

% Date of translated german file: 2007/08/07

\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 of {\LaTeX} extensions.  Today the package author has many
  macros available 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 that the
  package is loaded later.  This has led to the expectation that the
  order in which package are loaded would not be important.  Sadly
  this hope has not been fulfilled.
\end{Explain}

\section{About Package Dependencies}
\label{sec:scrlfile.dependency}
\begin{Explain}
  More and more frequently, different packages either newly define or
  redefine the same macro again.  In such a case the order in which a
  package is loaded becomes very important.  For the user it sometimes
  becomes very difficult to understand the behaviour, and in some
  cases the user wants only to react to the loading of a package. This
  too is not really a simple matter.

  Let us take the simple example of loading the package
  \Package{longtable} with a {\KOMAScript} document class.  The
  \Package{longtable} package defines table captions very well suited
  to the standard classes, but the captions are totally unsuitable for
  documents using {\KOMAScript} and also do not react to the options
  of the provided configuration commands.  In order to solve this
  problem, the \Package{longtable} package commands which are
  responsible for the table captions need to be redefined. However, by
  the time the \Package{longtable} package is loaded, the
  {\KOMAScript} class has already been processed.

  Until the present, the only way for {\KOMAScript} to solve this
  problem was to delay the redefinition until the beginning 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.  However, this is impossible
  since later at \Macro{begin}\PParameter{document} {\KOMAScript} will
  again overwrite the user definition with its own.  Therefore, the
  user too has to delay his definition with \Macro{AtBeginDocument}.
  
  Actually, {\KOMAScript} should not need to delay the redefinition
  until \Macro{begin}\PParameter{document}.  It would be enough to
  delay exactly until the package \Package{longtable} has been
  loaded. Unfortunately, the {\LaTeX} kernel 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 on any other file can be
  considered.  For example, the user can be warned if the not
  uncritical file \File{french.ldf} has been loaded.
  
  Although the package is particularly of interest 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 to and After Loading}
\label{sec:scrlfile.macros}

\Package{scrlfile} can execute actions both before and after the
loading of files. In the commands used to do this, distinctions are
made made between general files, classes, and packages.

\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} ensures that \PName{instructions} are
only executed before the next time \PName{file} is loaded.
\Macro{AfterFile} works in a similar fashion, and the
\PName{instructions} will be executed only after the \PName{file} has
been loaded.  If \PName{file} is never loaded then the
\PName{instructions} will never be executed.

\begin{Explain}
  In order to implement those features \Package{scrlfile} redefines
  the well known {\LaTeX} command \Macro{InputIfFileExists}. If this
  macro does not have the expected definition then \Package{scrlfile}
  issues a warning.  This is for the case that in future {\LaTeX}
  versions the macro can have a different definition, or that another
  package has already redefined it.
  
  The command \Macro{InputIfFileExists} is used by {\LaTeX} every time
  a file is to be loaded.  This is independent of whether the actual
  load command is \Macro{include}, \Macro{LoadClass},
  \Macro{documentclass}, \Macro{usepackage}, \Macro{RequirePackage},
  or similar. Exceptionally, the command
  \begin{lstlisting}
    \input foo
  \end{lstlisting}
  loads the file \texttt{foo} without utilizing
  \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 two commands work in 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 that 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} and \Macro{AfterPackage} work in 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 that the file extensions \File{.cls} and \File{.sty} can be
omitted.  The starred versions execute the \PName{instructions} not
only at next time that 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 redefine a macro of the
\Class{scrbook} class in such a way that does not work with newer
{\KOMAScript} versions.  New versions of \Package{hyperref} desist
from making these changes if a new {\KOMAScript} version is detected.
For the case that \Package{hyperref} is loaded at a later stage,
therefore, the code in \Class{scrbook} verifies that a acceptable
\Package{hyperref} version is used.  If not, the command issues a
warning.

At other places in three {\KOMAScript} classes the following can be
found:
\begin{lstlisting}
  \AfterPackage{caption2}{%
    \renewcommand*{\setcapindent}{%
\end{lstlisting}
After the package \Package{caption2} has been loaded, and only if it
has been loaded, {\KOMAScript} redefines its own command
\Macro{setcapindent}.  The exact code of the redefinition is not
important.  It should only be noted that \Package{caption2} takes
control of the \Macro{caption} macro and that therefore the normal
definition of the \Macro{setcapindent} macro would become ineffective.
The redefinition improves the collaboration with \Package{caption2}.

There are however also useful examples for normal {\LaTeX} user.
Suppose a document that should be available as a PS file, using
{\LaTeX} and dvips, as well as a PDF file, using pdf{\LaTeX}.  In
addition, the document should contain hyperlinks.  In the list of
tables there are entries longer than one line.  This is not a problem
for the pdf{\LaTeX} method, since here hyperlinks can be broken across
multiple lines.  However, if a \Package{hyperref} driver for dvips or
hyper{\TeX} is used then this is not possible.  In this case one
desires that for the \Package{hyperref} setup \Option{linktocpage} is
used. The decision which \Package{hyperref} driver to use happens
automatically via \File{hyperref.cfg}. The file has, for example, the
following content:
\begin{lstlisting}
  \ProvidesFile{hyperref.cfg}
  \@ifundefined{pdfoutput}{\ExecuteOptions{dvips}}
                          {\ExecuteOptions{pdftex}}
  \endinput
\end{lstlisting}

All the rest can now be left to \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 fairly long figure caption, but
      which does not employ the optional caption argument that would
      allow one to write a short caption in the list of figures.}
  \end{figure}
  \end{document}
\end{lstlisting}
If now the \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 another \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 a private
  \File{hyperref.cfg}.  If you do so, then instead of
  \Macro{usepackage} the macro \Macro{RequirePackage} ought be used
  (see \cite{latex:clsguide}).  The new lines have to be inserted
  directly after the \Macro{ProvidesFile} line, thus immediately prior
  to the execution of the options \Option{dvips} or \Option{pdftex}.
\end{Explain}%
\EndIndex{Package}{scrlfile}

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