<?xml version=“1.0”?> <!DOCTYPE doc [ <!ELEMENT doc (src | dest)*> <!ELEMENT src EMPTY> <!ELEMENT dest EMPTY> <!ATTLIST src ref IDREF #IMPLIED> <!ATTLIST dest id ID #IMPLIED> <!ENTITY dest “<dest id='foo'/>”> ]> <doc>

<src ref="foo"/>
&dest;
<src ref="foo"/>

</doc>