<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" onload="runTest()">
  <path id="foo" d="M150 50 L 450 50" />
  <text x="50" y="50">PASS</text>
  <pattern id="pat" patternUnits="userSpaceOnUse" x="0" y="0" width="400" height="400">
    <text>
      <textPath id="theTP" xlink:href="#foo">FAIL</textPath>
    </text>
  </pattern>
  <rect width="400" height="400" fill="url(#pat)" stroke="black" stroke-width="1"/>
  <script><![CDATA[
    function runTest() {
      var path = document.getElementById("foo");
      path.setAttribute("id", "bar");
    }
  ]]></script>
</svg>