This example is a bit pathological!

All the 'include' elements below have the same name of {http://www.w3.org/2001/XInclude}include:

<top xmlns="http://www.w3.org/2001/XInclude" 
     xmlns:parent="http://www.w3.org/2001/XInclude">

<!-- This one declares its own prefix 'xi' -->
<xi:include href="mydoc.xml" 
            xmlns:xi="http://www.w3.org/2001/XInclude"/>

<!-- This one declares its own prefix 'xmlinclude' -->
<xmlinclude:include href="mydoc.xml" 
                    xmlns:xmlinclude="http://www.w3.org/2001/XInclude"/>

<!-- This one declares defaults the namespace -->
<include href="mydoc.xml 
         xmlns="http://www.w3.org/2001/XInclude"/>

<!-- This one uses the default declared on 'top' -->
<include href="mydoc.xml"/>

<!-- This one uses the prefix 'parent' declared on 'top' -->
<parent:include href="mydoc.xml"/>

</top>