&lt;!DOCTYPE cmdsynopsis PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
          "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd"&gt;
&lt;cmdsynopsis&gt;
  &lt;command&gt;cd&lt;/command&gt;
  &lt;arg choice='req'&gt;&lt;replaceable&gt;directory&lt;/replaceable&gt;&lt;/arg&gt;
&lt;/cmdsynopsis&gt;