public function choose($val, $isMultiple = null)
    {
        $arguments = array(json_encode($val));
        if (null !== $isMultiple) {
            $arguments[] = (bool) $isMultiple ? 'true' : 'false';
        }

        $this->con->executeStep(
            sprintf('_sahi._setSelected(%s, %s)', $this->getAccessor(), implode(', ', $arguments))
        );
    }