/**
  * Dereference the file referenced by an assessmentSectionRef.
  *
  * @param AssessmentSectionRef $assessmentSectionRef An AssessmentSectionRef object to dereference.
  * @param FileResolver $resolver The Resolver object to be used to resolve AssessmentSectionRef's href attribute.
  * @throws XmlStorageException If an error occurs while dereferencing the referenced file.
  * @return XmlAssessmentSection The AssessmentSection referenced by $assessmentSectionRef.
  */
 protected static function resolveAssessmentSectionRef(AssessmentSectionRef $assessmentSectionRef, FileResolver $resolver)
 {
     try {
         $href = $resolver->resolve($assessmentSectionRef->getHref());
         $doc = new XmlDocument();
         $doc->load($href);
         return $doc->getDocumentComponent();
     } catch (XmlStorageException $e) {
         $msg = "An error occured while unreferencing file '{$href}'.";
         throw new XmlStorageException($msg);
     }
 }