A co-worker pointed out that the XML example that I used was not the best. It is not actually the DTD that is being included as an entity, but rather an external entity file. Here is a better example of the XML:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE studentPackage [
  <!ENTITY % StudentEntities PUBLIC "ISO 9999-9999//ENTITIES Student C
+haracter Entities 20100330//EN//XML" "http://www.student.org/Student_
+1-0/ent/StudentEntities">
  %StudentEntities;
]>
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