Multipart::getBoundary

protected function getBoundary($contentType = null)
{
	$type = $contentType ?: $this->getHeader('Content-Type');
	$type = explode(';', $type);
	$type = $type[0];
	switch ($type)
	{
		case self::MIXED:
			$prefix = 'mix';
			break;

		case self::ALTERNATIVE:
			$prefix = 'alt';
			break;

		default:
			$prefix = '';
	}

	return '-------' . $prefix . $this->uniqueString;
}