Xml tag insert in SQL (from a variable)

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SQL-Server-2008R2

GO  
DECLARE @myDoc xml;         
SET @myDoc = '<Root>         
    <ProductDescription ProductID="1" ProductName="Road Bike">         
        <Features>         
        </Features>         
    </ProductDescription>         
</Root>'  ;          
         
SET @myDoc.modify('         
insert <Maintenance>3 year parts and labor extended maintenance is available</Maintenance>   
after (/Root/ProductDescription/Features)[1]') ;  

SELECT @myDoc ; 

This works
--

But I need to insert the value from a variable. Now this doesn't work. Please suggest

declare @var varchar(50)
set @var='3 year parts and labor extended maintenance is available'  
SET @myDoc.modify('         
insert <Maintenance>'+ @var+'</Maintenance>   
after (/Root/ProductDescription/Features)[1]') ;  
SELECT @myDoc ; 

What I have tried:

I have tried:

1)declare @var varchar(50)
set @var='3 year parts and labor extended maintenance is available'
SET @myDoc.modify('
insert <maintenance>'+ @var+'
after (/Root/ProductDescription/Features)[1]') ;
SELECT @myDoc ;

2)
declare @var varchar(50)
set @var='3 year parts and labor extended maintenance is available'
SET @myDoc.modify('
insert <maintenance> with sql:variable("@var")
after (/Root/ProductDescription/Features)[1]') ;
SELECT @myDoc ;