docs: def _top_element(self):
          """Returns top XML element."""
          attrs = {"project-id": self.config["polarion-project-id"]}
          document_relative_path = self.config.get("requirements-document-relative-path")
          if document_relative_path:
              attrs["document-relative-path"] = document_relative_path
          top = etree.Element("requirements", attrs)
          return top