<!DOCTYPE HTML>
<html>
    <body>
        <p>The test passes if you see a green square.</p>
        <svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="200px" height="200px">
            <defs>
                <mask id="Mask">
                  <rect x="0" y="0" width="100" height="100" fill="white"  />
                </mask>
            </defs>
            <g id="isolator" mask="url(#Mask)">
                <rect x="0" y="0" width="200" height="200" style="fill: green;"/>
            </g>
        </svg>
    </body>
</html>