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@@ -1,74 +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-assertions">
- <title>Warnings and Assertions</title>
-
- <para>
-  When configuration problems are detectable in a module, it is a good idea to
-  write an assertion or warning. Doing so provides clear feedback to the user
-  and prevents errors after the build.
- </para>
-
- <para>
-  Although Nix has the <literal>abort</literal> and
-  <literal>builtins.trace</literal>
-  <link xlink:href="https://nixos.org/nix/manual/#ssec-builtins">functions</link>
-  to perform such tasks, they are not ideally suited for NixOS modules. Instead
-  of these functions, you can declare your warnings and assertions using the
-  NixOS module system.
- </para>
-
- <section xml:id="sec-assertions-warnings">
-  <title>Warnings</title>
-
-  <para>
-   This is an example of using <literal>warnings</literal>.
-  </para>
-
-<programlisting>
-<![CDATA[
-{ config, lib, ... }:
-{
-  config = lib.mkIf config.services.foo.enable {
-    warnings =
-      if config.services.foo.bar
-      then [ ''You have enabled the bar feature of the foo service.
-               This is known to cause some specific problems in certain situations.
-               '' ]
-      else [];
-  }
-}
-]]>
-</programlisting>
- </section>
-
- <section xml:id="sec-assertions-assertions">
-  <title>Assertions</title>
-
-  <para>
-   This example, extracted from the
-   <link xlink:href="https://github.com/NixOS/nixpkgs/blob/release-17.09/nixos/modules/services/logging/syslogd.nix">
-   <literal>syslogd</literal> module </link> shows how to use
-   <literal>assertions</literal>. Since there can only be one active syslog
-   daemon at a time, an assertion is useful to prevent such a broken system
-   from being built.
-  </para>
-
-<programlisting>
-<![CDATA[
-{ config, lib, ... }:
-{
-  config = lib.mkIf config.services.syslogd.enable {
-    assertions =
-      [ { assertion = !config.services.rsyslogd.enable;
-          message = "rsyslogd conflicts with syslogd";
-        }
-      ];
-  }
-}
-]]>
-</programlisting>
- </section>
-</section>