What is the correct syntax to sort a TableRow by two fields in DocuSign Gen?

I am trying to sort my OpportunityLineItems by two fields in a word template for Gen.I wanted to sort by Recurring_Product__c and then by UnitPrice. No matter what I try i keep getting errors. This is my current tag: 

<# <TableRow Select="./OpportunityLineItems" OrderBy="Recurring_Product__c ASC, UnitPrice ASC"/> #>

Which produces the OrderBy attribute is not declared. 

Any help is appreciated.