protected function _singleDatetime($options, $keep)
    {
        $off = array_diff($this->_datetimeParts, [$keep]);
        $off = array_combine(
            $off,
            array_fill(0, count($off), false)
        );

        $attributes = array_diff_key(
            $options,
            array_flip(array_merge($this->_datetimeOptions, ['value', 'empty']))
        );
        $options = $options + $off + [$keep => $attributes];

        if (isset($options['value'])) {
            $options['val'] = $options['value'];
        }

        return $options;
    }