chromium/third_party/blink/web_tests/svg/masking/mask-of-root.html

<!doctype HTML>
<svg mask="url(#m)">
  <mask id="m">
    <rect fill="white" width="100" height="100"/>
  </mask>
  <rect width="100" height="100" fill="green"/>
  <rect width="100" height="100" fill="red" x="100"/>
</svg>