<svg xmlns="http://www.w3.org/2000/svg">
<clipPath id="clip1" clipPathUnits="objectBoundingBox">
  <rect width="200" height="200"/>
</clipPath>

<rect width="400" height="400" fill="red" clip-path="url(#clip1)"/>
<rect width="200" height="200" fill="green"/>

<script>
var clip = document.getElementById("clip1");
var enumeration = clip.clipPathUnits;
enumeration.baseVal = 1; // Switch to userSpaceOnUse!
</script>
</svg>