<svg width="800" height="600" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
<defs>
    <clipPath id="myclip" clipPathUnits="objectBoundingBox">
        <path transform="scale(.5)" d="M 0 0 l 200 0 l 0 200 l -200 0 Z"/>
    </clipPath>
</defs>

<script>
if (window.layoutTestController)
    layoutTestController.waitUntilDone();

window.setTimeout("clickNow()", 0);

function clickNow() {
    if (window.eventSender) {
        eventSender.mouseMoveTo(150, 50);
        eventSender.mouseDown();
        eventSender.mouseUp();
    }

    if (window.layoutTestController) {
        layoutTestController.notifyDone();
    }
}

function mouseHandler(evt)
{
    var clip = document.getElementById("myclip");

    var enumeration = clip.clipPathUnits;
    enumeration.baseVal = 1; // Switch to userSpaceOnUse!
}
</script>

<g onclick="mouseHandler()" clip-path="url(#myclip)">
<rect x="0" y="0" width="200" height="200" fill="red"/>
<rect x="0" y="0" width="100" height="100" fill="green"/>
</g>

</svg>