<!DOCTYPE HTML>
<html>
<body>
<!-- Stretchy fences -->
<math>
<mfenced>
<mtable>
<mtr>
<mtd><mi>a</mi></mtd>
<mtd><mi>b</mi></mtd>
</mtr>
<mtd><mi>c</mi></mtd>
<mtd><mi>d</mi></mtd>
</mtable>
</mfenced>
</math>
</body>
</html>