<!DOCTYPE book [
<!ELEMENT book (doc*)>
<!ELEMENT doc (isid*)>
<!ELEMENT isid EMPTY>
<!ATTLIST isid myid ID #IMPLIED>
]>
<book>
<doc>
<isid myid="mine"/>
<isid myid="dup"/>
</doc>
<!-- including another XML document with IDs -->
<xinclude:include xmlns:xinclude="http://www.w3.org/2001/XInclude"
		 href="../ents/ids.xml"/>
</book>
