<!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>