code: protected function valueIsPossible($value)
      {
          $widgets = $this->getWidgets();
          for ($i = 0, $count = count($widgets); $i < $count; $i++) {
              if ($widgets[$i]->getAttribute('value') == $value) {
                  return true;
              }
          }
  
          return false;
      }
docs: Tests to see if a value is allowed.
  
  @param string    Attempted value.
  
  @return bool  True if a valid value.