docs: def _properties_element(self, parent_element):
          """Returns properties XML element."""
          testsuites_properties = etree.SubElement(parent_element, "properties")
  
          etree.SubElement(
              testsuites_properties,
              "property",
              {"name": "polarion-testrun-id", "value": str(self.testrun_id)},
          )
          etree.SubElement(
              testsuites_properties,
              "property",
              {"name": "polarion-project-id", "value": str(self.config["polarion-project-id"])},
          )
  
          for name, value in sorted(self.config["xunit_import_properties"].items()):
              if name == "polarion-lookup-method":
                  lookup_prop = str(value).lower()
                  if lookup_prop not in ("id", "name", "custom"):
                      raise Dump2PolarionException(
                          "Invalid value '{}' for the 'polarion-lookup-method' property".format(
                              str(value)
                          )
                      )
                  self._lookup_prop = lookup_prop
              elif name in ("polarion-testrun-id", "polarion-project-id"):
                  # this was already set
                  continue
              else:
                  etree.SubElement(
                      testsuites_properties, "property", {"name": name, "value": str(value)}
                  )
  
          return testsuites_properties