docs: def new(rId, reltype, target, target_mode=RTM.INTERNAL):
          """
          Return a new ``<Relationship>`` element.
          """
          xml = '<Relationship xmlns="%s"/>' % nsmap['pr']
          relationship = parse_xml(xml)
          relationship.set('Id', rId)
          relationship.set('Type', reltype)
          relationship.set('Target', target)
          if target_mode == RTM.EXTERNAL:
              relationship.set('TargetMode', RTM.EXTERNAL)
          return relationship