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+<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-replace-modules">
+
+<title>Replace Modules</title>
+
+<para>Modules that are imported can also be disabled.  The option
+  declarations and config implementation of a disabled module will be
+  ignored, allowing another to take it's place.  This can be used to
+  import a set of modules from another channel while keeping the rest
+  of the system on a stable release.</para>
+<para><literal>disabledModules</literal> is a top level attribute like
+  <literal>imports</literal>, <literal>options</literal> and
+  <literal>config</literal>.  It contains a list of modules that will
+  be disabled. This can either be the full path to the module or a
+  string with the filename relative to the modules path
+  (eg. &lt;nixpkgs/nixos/modules&gt; for nixos).
+  </para>
+
+<para>This example will replace the existing postgresql module with
+  the version defined in the nixos-unstable channel while keeping the
+  rest of the modules and packages from the original nixos channel.
+  This only overrides the module definition, this won't use postgresql
+  from nixos-unstable unless explicitly configured to do so.</para>
+
+<programlisting>
+{ config, lib, pkgs, ... }:
+
+{
+  disabledModules = [ "services/databases/postgresql.nix" ];
+
+  imports =
+    [ # Use postgresql service from nixos-unstable channel.
+      # sudo nix-channel --add http://nixos.org/channels/nixos-unstable nixos-unstable
+      &lt;nixos-unstable/nixos/modules/services/databases/postgresql.nix&gt;
+    ];
+
+  services.postgresql.enable = true;
+}
+</programlisting>
+
+<para>This example shows how to define a custom module as a
+  replacement for an existing module. Importing this module will
+  disable the original module without having to know it's
+  implementation details.</para>
+
+<programlisting>
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.programs.man;
+in
+
+{
+  disabledModules = [ "services/programs/man.nix" ];
+
+  options = {
+    programs.man.enable = mkOption {
+      type = types.bool;
+      default = true;
+      description = "Whether to enable manual pages.";
+    };
+  };
+
+  config = mkIf cfg.enabled {
+    warnings = [ "disabled manpages for production deployments." ];
+  };
+}
+</programlisting>
+
+</section>