1<?xml version="1.0"?> 2<!DOCTYPE book [ 3<!ELEMENT book (doc)*> 4<!ELEMENT doc (isid)*> 5<!ELEMENT isid EMPTY> 6<!ATTLIST isid myid ID #IMPLIED> 7]> 8<book> 9<doc> 10<isid myid="mine"/> 11<isid myid="dup"/> 12</doc> 13<!-- including another XML document with IDs --> 14<doc xml:base="../ents/ids.xml"> 15<isid myid="dup"/> 16<isid myid="foo"/> 17<isid myid="bar"/> 18</doc> 19</book> 20