<top xmlns:r="http://wwww.r-project.org"
     xmlns:xi= "http://www.w3.org/2003/XInclude">

 <xi:include href="basic.xml"/>
 <r:a>
   <!-- A comment -->
  Some text
  <![CDATA[
    x < 1 && y > 2
  ]]>
 </r:a>
 <?R plot(x) ?>
</top>