class_docstr: Base class used to display multiple child widgets.
code: def _validate_titles(self, proposal):
      return tuple(pad(proposal.value, "", len(self.children)))
  
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 2 for calling the _SelectionContainer obj's underlying member method code with example usage: obj._validate_titles(proposal) and returns: tuple