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