Xml element insertion in XML DATA

Adding element INTO the XML DATA
INSERT 
      Expression1 (
                 {AS first | AS last} INTO | after | before
                                    Expression2
                )
 
SET @xmlDoc.MODIFY('
    insert element UpdateDatetime {"2010-10-28T13:49:27.330"} before or after 
    (/t/AuditID)[1]
')
SET @xmlDoc.MODIFY('
   insert <UpdateDatetime>2010-10-28T13:49:27.330</UpdateDatetime>
	as last  or as first or      
	into(/t)[1]')
IF (@xmlDoc.exist('/t/UpdateDatetime')=0)
	BEGIN	
	SET @xmlDoc.MODIFY('
	insert <UpdateDatetime>2010-10-28T13:49:27.330</UpdateDatetime>
	as last       
	into(/t)[1]')
	END
 
*Adding element WITH dynamic DATA FROM the sp parameters WITH condition.
 
IF (@xmlDoc.exist('/t/UpdateDatetime')=0)
	BEGIN	
	SET @xmlDoc.MODIFY('
	insert element UpdateDatetime {sql:variable("@dtmCurrentDate")} 
	as last       
	into(/t)[1]')
	END