<!DOCTYPE html>
<html>
<style type="text/css">
  #outer {
    width: 100px;
    height: 100px;
    overflow: hidden;
  }

  #clipped {
    mask: url(#myMask);
    clip-path: url(#myClip);
  }

  #absolutePosition {
    position: absolute;
    top: 0;
    left: 0;
    width: 400px;
    height: 400px;
    background-color: blue;
  }
</style>

<body style="margin: 0px;">
  <div id="outer">
    <div id="clipped">
      <div id="absolutePosition">
      <!-- This should only be clipped by the mask, not by the 100x100
           overflow:hidden clip. -->
      </div>
    </div>
  </div>
  <svg height="0">
    <defs>
      <mask id="myMask" x="0" y="0" width="400" height="400" maskUnits="userSpaceOnUse">
        <rect x="0" y="0" width="100" height="100" style="stroke:none; fill: #ffffff"/>
        <rect x="100" y="100" width="100" height="100" style="stroke:none; fill: #ffffff"/>
        <rect x="200" y="200" width="100" height="100" style="stroke:none; fill: #ffffff"/>
      </mask>
      <clipPath id="myClip">
        <rect x="0" y="0" width="100" height="100"/>
        <rect x="100" y="100" width="100" height="100"/>
        <rect x="200" y="200" width="100" height="100"/>
        <!-- The forth rect should be clipped out -->
        <rect x="300" y="300" width="100" height="100"/>
      </clipPath>
    </defs>
  </svg>
</body>
</html>