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