docs: def remove_child(self, child_pid, reorder=False):
          """Remove a child from a PID concept."""
          super(PIDNodeOrdered, self).remove_child(child_pid)
          child_relations = self._resolved_pid.child_relations.filter(
              PIDRelation.relation_type == self.relation_type.id).order_by(
                  PIDRelation.index).all()
          if reorder:
              for idx, c in enumerate(child_relations):
                  c.index = idx