code: def validate_location_instance_valid_for_arc(sender, instance, action, reverse, pk_set, *args, **kwargs):
      '''
      Evaluates attempts to add location instances to arc, ensuring they are from same outline.
      '''
      if action == 'pre_add':
          if reverse:
              # Fetch arc definition through link.
              for apk in pk_set:
                  arc_node = ArcElementNode.objects.get(pk=apk)
                  if arc_node.parent_outline != instance.outline:
                      raise IntegrityError(_('Location instance must be from same outline as arc element.'))
          else:
              for lpk in pk_set:
                  loc_instance = LocationInstance.objects.get(pk=lpk)
                  if loc_instance.outline != instance.parent_outline:
                      raise IntegrityError(_('Location Instance must be from the same outline as arc element.')f validate_location_instance_valid_for_arc(sender, instance, action, reverse, pk_set, *args, **kwargs):
      '''
      Evaluates attempts to add location instances to arc, ensuring they are from same outline.
      '''
      if action == 'pre_add':
          if reverse:
              # Fetch arc definition through link.
              for apk in pk_set:
                  arc_node = ArcElementNode.objects.get(pk=apk)
                  if arc_node.parent_outline != instance.outline:
                      raise IntegrityError(_('Location instance must be from same outline as arc element.'))
          else:
              for lpk in pk_set:
                  loc_instance = LocationInstance.objects.get(pk=lpk)
                  if loc_instance.outline != instance.parent_outline:
                      raise IntegrityError(_('Location Instance must be from the same outline as arc element.'))
docs: Evaluates attempts to add location instances to arc, ensuring they are from same outline.