496 lines
15 KiB
XML
496 lines
15 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink"
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xml:id="chap-conventions">
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<title>Coding conventions</title>
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<section><title>Syntax</title>
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<itemizedlist>
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<listitem><para>Use 2 spaces of indentation per indentation level in
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Nix expressions, 4 spaces in shell scripts.</para></listitem>
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<listitem><para>Do not use tab characters, i.e. configure your
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editor to use soft tabs. For instance, use <literal>(setq-default
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indent-tabs-mode nil)</literal> in Emacs. Everybody has different
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tab settings so it’s asking for trouble.</para></listitem>
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<listitem><para>Use <literal>lowerCamelCase</literal> for variable
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names, not <literal>UpperCamelCase</literal>. TODO: naming of
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attributes in
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<filename>all-packages.nix</filename>?</para></listitem>
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<listitem><para>Function calls with attribute set arguments are
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written as
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<programlisting>
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foo {
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arg = ...;
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}
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</programlisting>
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not
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<programlisting>
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foo
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{
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arg = ...;
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}
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</programlisting>
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Also fine is
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<programlisting>
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foo { arg = ...; }
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</programlisting>
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if it's a short call.</para></listitem>
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<listitem><para>In attribute sets or lists that span multiple lines,
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the attribute names or list elements should be aligned:
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<programlisting>
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# A long list.
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list =
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[ elem1
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elem2
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elem3
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];
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# A long attribute set.
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attrs =
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{ attr1 = short_expr;
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attr2 =
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if true then big_expr else big_expr;
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};
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# Alternatively:
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attrs = {
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attr1 = short_expr;
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attr2 =
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if true then big_expr else big_expr;
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};
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</programlisting>
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</para></listitem>
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<listitem><para>Short lists or attribute sets can be written on one
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line:
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<programlisting>
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# A short list.
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list = [ elem1 elem2 elem3 ];
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# A short set.
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attrs = { x = 1280; y = 1024; };
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</programlisting>
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</para></listitem>
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<listitem><para>Breaking in the middle of a function argument can
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give hard-to-read code, like
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<programlisting>
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someFunction { x = 1280;
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y = 1024; } otherArg
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yetAnotherArg
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</programlisting>
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(especially if the argument is very large, spanning multiple
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lines).</para>
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<para>Better:
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<programlisting>
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someFunction
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{ x = 1280; y = 1024; }
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otherArg
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yetAnotherArg
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</programlisting>
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or
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<programlisting>
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let res = { x = 1280; y = 1024; };
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in someFunction res otherArg yetAnotherArg
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</programlisting>
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</para></listitem>
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<listitem><para>The bodies of functions, asserts, and withs are not
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indented to prevent a lot of superfluous indentation levels, i.e.
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<programlisting>
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{ arg1, arg2 }:
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assert system == "i686-linux";
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stdenv.mkDerivation { ...
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</programlisting>
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not
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<programlisting>
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{ arg1, arg2 }:
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assert system == "i686-linux";
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stdenv.mkDerivation { ...
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</programlisting>
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</para></listitem>
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<listitem><para>Function formal arguments are written as:
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<programlisting>
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{ arg1, arg2, arg3 }:
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</programlisting>
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but if they don't fit on one line they're written as:
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<programlisting>
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{ arg1, arg2, arg3
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, arg4, ...
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, # Some comment...
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argN
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}:
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</programlisting>
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</para></listitem>
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<listitem><para>Functions should list their expected arguments as
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precisely as possible. That is, write
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<programlisting>
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{ stdenv, fetchurl, perl }: <replaceable>...</replaceable>
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</programlisting>
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instead of
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<programlisting>
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args: with args; <replaceable>...</replaceable>
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</programlisting>
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or
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<programlisting>
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{ stdenv, fetchurl, perl, ... }: <replaceable>...</replaceable>
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</programlisting>
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</para>
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<para>For functions that are truly generic in the number of
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arguments (such as wrappers around <varname>mkDerivation</varname>)
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that have some required arguments, you should write them using an
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<literal>@</literal>-pattern:
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<programlisting>
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{ stdenv, doCoverageAnalysis ? false, ... } @ args:
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stdenv.mkDerivation (args // {
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<replaceable>...</replaceable> if doCoverageAnalysis then "bla" else "" <replaceable>...</replaceable>
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})
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</programlisting>
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instead of
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<programlisting>
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args:
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args.stdenv.mkDerivation (args // {
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<replaceable>...</replaceable> if args ? doCoverageAnalysis && args.doCoverageAnalysis then "bla" else "" <replaceable>...</replaceable>
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})
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</programlisting>
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</para></listitem>
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</itemizedlist>
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</section>
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<section><title>File naming and organisation</title>
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<para>Names of files and directories should be in lowercase, with
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dashes between words — not in camel case. For instance, it should be
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<filename>all-packages.nix</filename>, not
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<filename>allPackages.nix</filename> or
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<filename>AllPackages.nix</filename>.</para>
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<para>Each package should be stored in its own directory somewhere in
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the <filename>pkgs/</filename> tree, i.e. in
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<filename>pkgs/<replaceable>category</replaceable>/<replaceable>subcategory</replaceable>/<replaceable>...</replaceable>/<replaceable>pkgname</replaceable></filename>.
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Below are some rules for picking the right category for a package.
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Many packages fall under several categories; what matters is the
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<emphasis>primary</emphasis> purpose of a package. For example, the
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<literal>libxml2</literal> package builds both a library and some
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tools; but it’s a library foremost, so it goes under
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<filename>pkgs/development/libraries</filename>.</para>
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<para>When in doubt, consider refactoring the
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<filename>pkgs/</filename> tree, e.g. creating new categories or
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splitting up an existing category.</para>
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<variablelist>
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<varlistentry>
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<term>If it’s used to support <emphasis>software development</emphasis>:</term>
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<listitem>
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<variablelist>
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<varlistentry>
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<term>If it’s a <emphasis>library</emphasis> used by other packages:</term>
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<listitem>
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<para><filename>development/libraries</filename> (e.g. <filename>libxml2</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>compiler</emphasis>:</term>
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<listitem>
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<para><filename>development/compilers</filename> (e.g. <filename>gcc</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s an <emphasis>interpreter</emphasis>:</term>
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<listitem>
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<para><filename>development/interpreters</filename> (e.g. <filename>guile</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a (set of) development <emphasis>tool(s)</emphasis>:</term>
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<listitem>
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<variablelist>
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<varlistentry>
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<term>If it’s a <emphasis>parser generator</emphasis> (including lexers):</term>
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<listitem>
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<para><filename>development/tools/parsing</filename> (e.g. <filename>bison</filename>, <filename>flex</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>build manager</emphasis>:</term>
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<listitem>
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<para><filename>development/tools/build-managers</filename> (e.g. <filename>gnumake</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>development/tools/misc</filename> (e.g. <filename>binutils</filename>)</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>development/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a (set of) <emphasis>tool(s)</emphasis>:</term>
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<listitem>
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<para>(A tool is a relatively small program, especially one intented
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to be used non-interactively.)</para>
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<variablelist>
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<varlistentry>
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<term>If it’s for <emphasis>networking</emphasis>:</term>
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<listitem>
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<para><filename>tools/networking</filename> (e.g. <filename>wget</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s for <emphasis>text processing</emphasis>:</term>
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<listitem>
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<para><filename>tools/text</filename> (e.g. <filename>diffutils</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>system utility</emphasis>, i.e.,
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something related or essential to the operation of a
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system:</term>
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<listitem>
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<para><filename>tools/system</filename> (e.g. <filename>cron</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s an <emphasis>archiver</emphasis> (which may
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include a compression function):</term>
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<listitem>
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<para><filename>tools/archivers</filename> (e.g. <filename>zip</filename>, <filename>tar</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>compression</emphasis> program:</term>
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<listitem>
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<para><filename>tools/compression</filename> (e.g. <filename>gzip</filename>, <filename>bzip2</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>security</emphasis>-related program:</term>
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<listitem>
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<para><filename>tools/security</filename> (e.g. <filename>nmap</filename>, <filename>gnupg</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>tools/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>shell</emphasis>:</term>
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<listitem>
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<para><filename>shells</filename> (e.g. <filename>bash</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>server</emphasis>:</term>
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<listitem>
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<variablelist>
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<varlistentry>
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<term>If it’s a web server:</term>
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<listitem>
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<para><filename>servers/http</filename> (e.g. <filename>apache-httpd</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s an implementation of the X Windowing System:</term>
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<listitem>
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<para><filename>servers/x11</filename> (e.g. <filename>xorg</filename> — this includes the client libraries and programs)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>servers/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>desktop environment</emphasis>
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(including <emphasis>window managers</emphasis>):</term>
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<listitem>
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<para><filename>desktops</filename> (e.g. <filename>kde</filename>, <filename>gnome</filename>, <filename>enlightenment</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s an <emphasis>application</emphasis>:</term>
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<listitem>
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<para>A (typically large) program with a distinct user
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interface, primarily used interactively.</para>
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<variablelist>
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<varlistentry>
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<term>If it’s a <emphasis>version management system</emphasis>:</term>
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<listitem>
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<para><filename>applications/version-management</filename> (e.g. <filename>subversion</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s for <emphasis>video playback / editing</emphasis>:</term>
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<listitem>
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<para><filename>applications/video</filename> (e.g. <filename>vlc</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s for <emphasis>graphics viewing / editing</emphasis>:</term>
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<listitem>
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<para><filename>applications/graphics</filename> (e.g. <filename>gimp</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s for <emphasis>networking</emphasis>:</term>
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<listitem>
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<variablelist>
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<varlistentry>
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<term>If it’s a <emphasis>mailreader</emphasis>:</term>
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<listitem>
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<para><filename>applications/networking/mailreaders</filename> (e.g. <filename>thunderbird</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>newsreader</emphasis>:</term>
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<listitem>
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<para><filename>applications/networking/newsreaders</filename> (e.g. <filename>pan</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s a <emphasis>web browser</emphasis>:</term>
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<listitem>
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<para><filename>applications/networking/browsers</filename> (e.g. <filename>firefox</filename>)</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>applications/networking/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>Else:</term>
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<listitem>
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<para><filename>applications/misc</filename></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term>If it’s <emphasis>data</emphasis> (i.e., does not have a
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straight-forward executable semantics):</term>
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||
<listitem>
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<variablelist>
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||
<varlistentry>
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||
<term>If it’s a <emphasis>font</emphasis>:</term>
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||
<listitem>
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||
<para><filename>data/fonts</filename></para>
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</listitem>
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||
</varlistentry>
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<varlistentry>
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||
<term>If it’s related to <emphasis>SGML/XML processing</emphasis>:</term>
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<listitem>
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||
<variablelist>
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||
<varlistentry>
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<term>If it’s an <emphasis>XML DTD</emphasis>:</term>
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||
<listitem>
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||
<para><filename>data/sgml+xml/schemas/xml-dtd</filename> (e.g. <filename>docbook</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s an <emphasis>XSLT stylesheet</emphasis>:</term>
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||
<listitem>
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||
<para>(Okay, these are executable...)</para>
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<para><filename>data/sgml+xml/stylesheets/xslt</filename> (e.g. <filename>docbook-xsl</filename>)</para>
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||
</listitem>
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||
</varlistentry>
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||
</variablelist>
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||
</listitem>
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||
</varlistentry>
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||
</variablelist>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>If it’s a <emphasis>game</emphasis>:</term>
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||
<listitem>
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||
<para><filename>games</filename></para>
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||
</listitem>
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||
</varlistentry>
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||
<varlistentry>
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||
<term>Else:</term>
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||
<listitem>
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||
<para><filename>misc</filename></para>
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||
</listitem>
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||
</varlistentry>
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||
</variablelist>
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||
</section>
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</chapter>
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