chromium/third_party/blink/web_tests/svg/custom/textPath-set-id.svg

<svg xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" onload="runTest()">
  <defs>
    <path d="M150 50 L 450 50" />
  </defs>
  <text>
    <textPath id="theTP" xlink:href="#foo">PASS</textPath>
  </text>
  <script><![CDATA[
    function runTest() {
      var path = document.getElementsByTagName("path")[0];
      path.setAttribute("id","foo");
    }
  ]]></script>
</svg>