[relax-ng] Compact syntax DTD info

How (if at all) should the following be represented in the compact syntax?

<!DOCTYPE element [
<!ENTITY ent SYSTEM "http://www.example.com/ent" NDATA jpeg>
]>
<element name="foo"
         datatypeLibrary="http://www.w3.org/2001/XMLSchema-datatypes"
         xmlns="http://relaxng.org/ns/structure/1.0">
  <value type="ENTITY">ent</value>
</element>


James