docs: def insert_child(self, child_pid, index=-1):
          """Insert a Version child PID."""
          if child_pid.status != PIDStatus.REGISTERED:
              raise PIDRelationConsistencyError(
                  "Version PIDs should have status 'REGISTERED'. Use "
                  "insert_draft_child to insert 'RESERVED' draft PID.")
          with db.session.begin_nested():
              # if there is a draft and "child" is inserted as the last version,
              # it should be inserted before the draft.
              draft = self.draft_child
              if draft and index == -1:
                  index = self.index(draft)
              super(PIDNodeVersioning, self).insert_child(child_pid, index=index)
              self.update_redirect()