<svg xmlns="http://www.w3.org/2000/svg" xmlns:h="http://www.w3.org/1999/xhtml">
  <title>mask with only an empty container with a filter</title>
  <h:link rel="help" href="https://drafts.fxtf.org/css-masking-1/#svg-masks"/>
  <h:link rel="match" href="reference/mask-green-square-001-ref.svg"/>

  <filter id="double" x="0" y="0" width="200" height="200" filterUnits="userSpaceOnUse">
    <feOffset dy="100"/>
    <feMerge>
      <feMergeNode/>
      <feMergeNode in="SourceGraphic"/>
    </feMerge>
  </filter>
  <filter id="f" x="0" y="0" width="200" height="200" filterUnits="userSpaceOnUse">
    <feFlood flood-color="#fff"/>
  </filter>
  <mask id="m" x="50" y="50" width="100" height="100" maskUnits="userSpaceOnUse">
    <g filter="url(#f)"/>
  </mask>

  <rect width="100" height="200" fill="green" mask="url(#m)"/>
  <rect width="100" height="100" x="100" fill="green" mask="url(#m)"
	filter="url(#double)"/>
</svg>