BodyStructure::getDispositionIndex

protected function getDispositionIndex()
{
	switch ($this->getType())
	{
		case 'multipart':
			return 3;
		case 'message':
			return 'rfc822' === $this->getSubtype() ? 11 : 8;
		case 'text':
			return 9;
		default:
			return 8;
	}
}