What is order of attachments when Print Receivables Transactions merges pdf into single file?

Summary:

What is order of attachments when Print Receivables Transactions merges pdf into single file?

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Assume attachment a, attachment b, and attachment c are uploaded to invoice transaction. All attachments are pdfs. Print Receivables Transactions will merge all files into single pdf file with invoice pdf first before attachment pdfs. What is standard order of attachment pdfs after invoice pdf? Is it based on order as to when each attachment is uploaded? What if user wants order in merged pdf to be invoice pdf, attachment b, attachment c, then attachment a? Is there any standard functionality to control this order?