MSSQL XML

USE MySQLDB;  
GO  
DECLARE @myDoc XML;         
SET @myDoc = '<QBXML>         
    <QBXMLMsgsRq onError="stopOnError">                  
    </QBXMLMsgsRq>         
</QBXML>'; 

SET @myDoc.modify('         
insert

    -- instead of inserting string here.. I would like to insert here the query I made above

into (/QBXML/QBXMLMsgsRq)[1]');

SELECT @myDoc;
Terrible Teira