code: def export_child_lane_set(parent_xml_element, child_lane_set, plane_element):
          
          lane_set_xml = eTree.SubElement(parent_xml_element, consts.Consts.lane_set)
          for key, value in child_lane_set[consts.Consts.lanes].items():
              BpmnDiagramGraphExport.export_lane(lane_set_xml, key, value, plane_element)
docs: Creates 'childLaneSet' element for exported BPMN XML file.
  
          :param parent_xml_element: an XML element, parent of exported 'childLaneSet' element,
          :param child_lane_set: dictionary with exported 'childLaneSet' element attributes and child elements,
          :param plane_element: XML object, representing 'plane' element of exported BPMN 2.0 XML.