<literal>ID=centos</literal> an
assignment of <literal>ID_LIKE="rhel
fedora"</literal> would be
- appropriate. For an operating systemd
+ appropriate. For an operating system
with <literal>ID=ubuntu</literal> an
assignment of
<literal>ID_LIKE=debian</literal> is
accommodate for rolling releases. In this case VERSION
and VERSION_ID may be unset. Applications should not
rely on these fields to be set.</para>
+
+ <para>Operating system vendors may extend the file
+ format and introduce new fields. It is highly
+ recommended to prefix new fields with an OS specific
+ name in order to avoid name clashes. Applications
+ reading this file must ignore unknown fields. Example:
+ <literal>DEBIAN_BTS="debbugs://bugs.debian.org/"</literal></para>
</refsect1>
<refsect1>