1<element name="root" xmlns="http://relaxng.org/ns/structure/1.0">
2  <choice>
3    <element name="child">
4      <attribute name="type">
5        <value>Foo</value>
6      </attribute>
7      <!-- Define stuff that's only valid when type is "Foo" -->
8    </element>
9    <element name="child">
10      <attribute name="type">
11        <value>Bar</value>
12      </attribute>
13      <!-- Define stuff that's only valid when type is "Bar" -->
14    </element>
15  </choice>
16</element>
17