1  <?xml version="1.0"?>
 2  <!DOCTYPE doc [
 3  <!ELEMENT doc (src | dest)*>
 4  <!ELEMENT src EMPTY>
 5  <!ELEMENT dest EMPTY>
 6  <!ATTLIST src ref IDREF #IMPLIED>
 7  <!ATTLIST dest id ID #IMPLIED>
 8  ]>
 9  <doc>
10    <src ref="foo"/>
11    <dest id="foo"/>
12    <src ref="foo"/>
13  </doc>