class_docstr: Base class used to display multiple child widgets.
code: def _reset_selected_index(self):
      if (
          self.selected_index is not None
          and len(self.children) < self.selected_index
      ):
          self.selected_index = None
  
imports: from .widget_box import Box
  from .widget import register
  from .widget_core import CoreWidget
  from traitlets import Unicode, Dict, CInt, TraitError, validate, observe
  from .trait_types import TypedTuple
  from itertools import chain, repeat, islice
label_desc: Use image node_id 4 for calling the _SelectionContainer obj's underlying member method code with example usage: obj._reset_selected_index() without return types