1<?xml version="1.0"?> 2<doc> 3 <xi:include xmlns:xi="http://www.w3.org/2001/XInclude" href="b.xml"> 4 <xi:fallback><xi:include href="c.xml"> 5 <xi:fallback/> 6 </xi:include></xi:fallback> 7 </xi:include> 8</doc> 9