No duplicates element's values in a list of element

Hi!

let's suppose that we have this xml:
...
<name>name1</name>
<name>name2</name>
...
<name>nameN</name>

Is there a ddt rule that forces to don't have duplicate value of name?
or: i must write a function (using jdom) that recovers all the elements 
and controls if there is a duplicate value?
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