Including relax-ng schema in my schema?

In reading the spec and tutorial, it is not clear to me how I would 
define my own pattern which contains the relax-ng pattern.  Here is 
basically what I want to do:

<MyDocument>
<!-- ... -->
 <StructureDefinition xmlns:rng="http://relaxng.org/ns/structure/0.9">
  <rng:grammar ns="http://mydocument.com/ns/1.0">
        <rng:start><rng:ref name="name" /></rng:start>
        <rng:define name="name">
            <rng:element name="Name"><rng:text /></rng:element>
        </rng:define>
   </rng:grammar>
 </StructureDefinition>
<!-- ... -->
</MyDocument>

How exactly do I enable this in the relax-ng schema for MyDocument?  In 
a DTD, I might do this:

<!ENTITY % rng SYSTEM "rng.dtd">
%rng;
<!ELEMENT MyDocument (StructureDefinition)>
<!ELEMENT StructureDefinition (grammar|element)>


Thanks in advance,

Matthew MacKenzie
XML Global