code: def _adjust_parent_stack(fsh, prev, parents):
      
      if prev is None:
          return
  
      if fsh.fold_scope.trigger_level < prev.fold_scope.trigger_level:
          diff = prev.fold_scope.trigger_level - fsh.fold_scope.trigger_level
          del parents[-diff:]
      elif fsh.fold_scope.trigger_level > prev.fold_scope.trigger_level:
          parents.append(prev)
      elif fsh.fold_scope.trigger_level == prev.fold_scope.trigger_level:
          pass
docs: Adjust the parent stack in-place as the trigger level changes.
  
      Parameters
      ----------
      fsh : :class:`FoldScopeHelper`
          The :class:`FoldScopeHelper` object to act on.
      prev : :class:`FoldScopeHelper`
          The previous :class:`FoldScopeHelper` object.
      parents : list of :class:`FoldScopeHelper`
          The current list of parent objects.
  
      Returns
      -------
      None