<<< native
[ EDelimited "(" ")" [ Right (EIdentifier "x") ] ]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mo stretchy="true" form="prefix">(</mo>
    <mi>x</mi>
    <mo stretchy="true" form="postfix">)</mo>
  </mrow>
</math>