docs: def message_archive(self, project_id, category_id=None):
          """
          This will return a summary record for each message in a project. If
          you specify a category_id, only messages in that category will be
          returned. (Note that a summary record includes only a few bits of
          information about a post, not the complete record.)
          """
          path = '/projects/%u/msg/archive' % project_id
          req = ET.Element('request')
          ET.SubElement(req, 'project-id').text = str(int(project_id))
          if category_id is not None:
              ET.SubElement(req, 'category-id').text = str(int(category_id))
          return self._request(path, req)