trisquel-icecat/icecat/layout/reftests/svg/clipPath-basic-shape-transform-ref.html

<svg style="width: 400px; height: 400px">
  <mask id="m1">
    <rect x="100" y="90" width="200" height="200" fill="blue" style="clip-path: inset(50px 50px)"></rect>
  </mask>
  <rect width="400" height="400" mask="url(#m1)"></rect>
</svg>