<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<defs>
    <path id="star" d="m 100,0 60,170 -160,-110 200,0 -170,110 z" transform="translate(70,40)"/>
    <clipPath id="clip">
        <!-- nothing should be visible, containers are not allowed in clipPath -->
        <g>
            <use xlink:href="#star"/>
        </g>
    </clipPath>
</defs>

<rect x="40" y="40" height="300" width="300" style="fill:green;clip-path:url(#clip);"/>
</svg>