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