+<para>Preferences are a strong power in the hands of a system administrator
+but they can become also their biggest nightmare if used without care!
+APT will not questioning the preferences so wrong settings will therefore
+lead to uninstallable packages or wrong decisions while upgrading packages.
+Even more problems will arise if multiply distribution releases are mixed
+without a good understanding of the following paragraphs.
+Packages included in a specific release aren't tested in and
+therefore doesn't always work as expected in older or newer releases or
+together with other packages from different releases.
+You have been warned.</para>
+
+<para>Note that the files in the <filename>/etc/apt/preferences.d</filename>
+directory are parsed in alphanumeric ascending order and need to obey the
+following naming convention: The files have no or "<literal>pref</literal>"
+as filename extension and which only contain alphanumeric, hyphen (-),
+underscore (_) and period (.) characters - otherwise they will be silently
+ignored.</para>
+