1<!DOCTYPE doc [
2<!ELEMENT doc (src | dest)*>
3<!ELEMENT src EMPTY>
4<!ELEMENT dest EMPTY>
5<!ATTLIST src ref IDREF #IMPLIED>
6<!ATTLIST dest id ID #IMPLIED>
7]>
8<doc>
9  <src ref="foo"/>
10  <dest id="foo"/>
11  <src ref="foo"/>
12</doc>
13
14