code: def get_collection(self, journal):
          
          conference = ''
          for tag in self.document.getElementsByTagName('conference'):
              conference = xml_to_text(tag)
          if conference or journal == "International Journal of Modern Physics: Conference Series":
              return [('a', 'HEP'), ('a', 'ConferencePaper')]
          elif self._get_article_type() == "review-article":
              return [('a', 'HEP'), ('a', 'Review')]
          else:
              return [('a', 'HEP'), ('a', 'Published')]
docs: Return this articles' collection.