<?xml version="1.0"?>
<sparql xmlns="http://www.w3.org/2005/sparql-results#">
    <head custom="foo">
        <variable name="s"/>
    </head>
    <results custom="foo">
        <result>
            <binding name="s">
                <uri>http://example.com/a</uri>
            </binding>
        </result>
    </results>
</sparql>