def METHOD_NAME(self):
    dtd = self.parse("dtd/prefix_namespace.dtd")
    self.assertEqual(2, len(dtd.elements))
    self.assertEqual("ns", dtd.elements[0].prefix)
    self.assertEqual("ns", dtd.elements[1].prefix)
    self.assertIn("ns", dtd.elements[0].ns_map)
    self.assertEqual("http://www.example.com/", dtd.elements[0].ns_map["ns"])
    self.assertNotIn("ns", dtd.elements[1].ns_map)