code: def allow_choice_custom_value(self):
          
          if 'choiceInfo' not in self.dto[self.name]:
              raise GPException('not a choice parameter')
          return self._is_string_true(self.dto[self.name]['choiceInfo']['choiceAllowCustom'])
docs: Returns boolean indicating whether choice parameter supports custom value.
  
          If choice parameter supports custom value, user can provide parameter value
          other than those provided in choice list.