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diff --git a/nixos/doc/manual/development/option-def.xml b/nixos/doc/manual/development/option-def.xml
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@@ -1,99 +0,0 @@
-<section xmlns="http://docbook.org/ns/docbook"
-        xmlns:xlink="http://www.w3.org/1999/xlink"
-        xmlns:xi="http://www.w3.org/2001/XInclude"
-        version="5.0"
-        xml:id="sec-option-definitions">
- <title>Option Definitions</title>
-
- <para>
-  Option definitions are generally straight-forward bindings of values to
-  option names, like
-<programlisting>
-config = {
-  services.httpd.enable = true;
-};
-</programlisting>
-  However, sometimes you need to wrap an option definition or set of option
-  definitions in a <emphasis>property</emphasis> to achieve certain effects:
- </para>
-
- <simplesect xml:id="sec-option-definitions-delaying-conditionals">
-  <title>Delaying Conditionals</title>
-  <para>
-   If a set of option definitions is conditional on the value of another
-   option, you may need to use <varname>mkIf</varname>. Consider, for instance:
-<programlisting>
-config = if config.services.httpd.enable then {
-  environment.systemPackages = [ <replaceable>...</replaceable> ];
-  <replaceable>...</replaceable>
-} else {};
-</programlisting>
-   This definition will cause Nix to fail with an “infinite recursion”
-   error. Why? Because the value of
-   <option>config.services.httpd.enable</option> depends on the value being
-   constructed here. After all, you could also write the clearly circular and
-   contradictory:
-<programlisting>
-config = if config.services.httpd.enable then {
-  services.httpd.enable = false;
-} else {
-  services.httpd.enable = true;
-};
-</programlisting>
-   The solution is to write:
-<programlisting>
-config = mkIf config.services.httpd.enable {
-  environment.systemPackages = [ <replaceable>...</replaceable> ];
-  <replaceable>...</replaceable>
-};
-</programlisting>
-   The special function <varname>mkIf</varname> causes the evaluation of the
-   conditional to be “pushed down” into the individual definitions, as if
-   you had written:
-<programlisting>
-config = {
-  environment.systemPackages = if config.services.httpd.enable then [ <replaceable>...</replaceable> ] else [];
-  <replaceable>...</replaceable>
-};
-</programlisting>
-  </para>
- </simplesect>
-
- <simplesect xml:id="sec-option-definitions-setting-priorities">
-  <title>Setting Priorities</title>
-  <para>
-   A module can override the definitions of an option in other modules by
-   setting a <emphasis>priority</emphasis>. All option definitions that do not
-   have the lowest priority value are discarded. By default, option definitions
-   have priority 1000. You can specify an explicit priority by using
-   <varname>mkOverride</varname>, e.g.
-<programlisting>
-services.openssh.enable = mkOverride 10 false;
-</programlisting>
-   This definition causes all other definitions with priorities above 10 to be
-   discarded. The function <varname>mkForce</varname> is equal to
-   <varname>mkOverride 50</varname>.
-  </para>
- </simplesect>
-
- <simplesect xml:id="sec-option-definitions-merging">
-  <title>Merging Configurations</title>
-  <para>
-   In conjunction with <literal>mkIf</literal>, it is sometimes useful for a
-   module to return multiple sets of option definitions, to be merged together
-   as if they were declared in separate modules. This can be done using
-   <varname>mkMerge</varname>:
-<programlisting>
-config = mkMerge
-  [ # Unconditional stuff.
-    { environment.systemPackages = [ <replaceable>...</replaceable> ];
-    }
-    # Conditional stuff.
-    (mkIf config.services.bla.enable {
-      environment.systemPackages = [ <replaceable>...</replaceable> ];
-    })
-  ];
-</programlisting>
-  </para>
- </simplesect>
-</section>