Use/include a value from another node

I have an XML file, like this:

<area1>
    <settings>
        <setting name="to_include">value</setting>
    </settings>
</area1>
<area2>
    <settings>
        <setting name="where_to_include">?????</setting>
    </settings>
</area2>

I want to include the value of the setting node "to_include" as value of setting node "where_to_include". How could I do it? XInclude? XPath? XLink? Other?