html/semantics/tabular-data/the-tr-element/cells.html

<!DOCTYPE html>
<meta charset="utf-8">
<title>HTMLTableRowElement#cells</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>

<div id="log"></div>

<table>
  <tr id="testTr">
    <td>First</td>
    <div><td>Second</td></div>
    <td>Third
      <table>
        <tr><td>Nested first</td></tr>
      </table>
    </td>
    <img>
  </tr>
</table>
<script>
var tr = document.getElementById("testTr");

test(function () {
  tr.insertBefore(document.createElementNS("foo", "td"), tr.children[1]);
  assert_array_equals(tr.cells, [tr.children[0], tr.children[2], tr.children[3]]);
}, "HTMLTableRowElement cells ignores nested tables and non-HTML elements");
</script>