Dynamics AX 2009 - Differentiating between Invoice and Credit Note

I was wondering whether or not it was possible to differentiate between an Invoice and Credit Note when using Dynamics AX 2009? As my understanding is that they get printed the same with the exception that a Credit Note contains negative values? The reason for asking is because I wish to get them out of the system in XML format using the AIF but transform each differently using different XSLT documents