class_docstr: Base class used to display multiple child widgets.
class_docstr_tok: ["Base","class","used","to","display","multiple","child","widgets","."]
code: def _validated_index(self, proposal):
      if proposal.value is None or 0 <= proposal.value < len(
          self.children
      ):
          return proposal.value
      else:
          raise TraitError("Invalid selection: index out of bounds")
  
file_path: catboost/contrib/python/ipywidgets/py2/ipywidgets/widgets/widget_selectioncontainer.py
imports: from .widget_box import Box
  from .widget import register
  from .widget_core import CoreWidget
  from traitlets import Unicode, Dict, CInt, TraitError, validate
  from ipython_genutils.py3compat import unicode_type
label_desc: Use image node_id 1 for calling the _SelectionContainer obj's underlying member method code with example usage: obj._validated_index(proposal) and returns: proposal