1  <?xml version="1.0" encoding="UTF-8"?>
 2  <grammar xmlns="http://relaxng.org/ns/structure/1.0">
 3    <start>
 4      <ref name="e2"/>
 5    </start>
 6    <define name="e2">
 7      <element name="e2">
 8        <element name="e3">
 9          <text/>
10        </element>
11      </element>
12    </define>
13  </grammar>