def get_documents(self, subtypes=None, refresh=False):
        """Return list of author's publications using ScopusSearch, which
        fit a specified set of document subtypes.
        """
        search = ScopusSearch('au-id({})'.format(self.identifier), refresh)
        if subtypes:
            return [p for p in search.results if p.subtype in subtypes]
        else:
            return search.results