code: def _getSelfVerificationVocabulary(self):
          
          bsve = self.bika_setup.getSelfVerificationEnabled()
          bsve = _('Yes') if bsve else _('No')
          bsval = "%s (%s)" % (_("System default"), bsve)
          items = [(-1, bsval), (0, _('No')), (1, _('Yes'))]
          return IntDisplayList(list(items))
docs: Returns a DisplayList with the available options for the
          self-verification list: 'system default', 'true', 'false'
          :returns: DisplayList with the available options for the
          self-verification list