mphantomB1.test

<<< native
[ EIdentifier "A"
, EPhantom (EIdentifier "A")
, EIdentifier "A"
, ESymbol Bin "+"
, EFraction
    NormalFrac
    (EGrouped
       [ ENumber "1"
       , ESymbol Bin "+"
       , ENumber "2"
       , ESymbol Bin "+"
       , ENumber "3"
       ])
    (EGrouped
       [ ENumber "1"
       , ESymbol Bin "+"
       , EPhantom (EGrouped [ ENumber "2" , ESymbol Bin "+" ])
       , ENumber "3"
       ])
]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mi>A</mi>
    <mphantom>
      <mi>A</mi>
    </mphantom>
    <mi>A</mi>
    <mo>+</mo>
    <mfrac>
      <mrow>
        <mn>1</mn>
        <mo>+</mo>
        <mn>2</mn>
        <mo>+</mo>
        <mn>3</mn>
      </mrow>
      <mrow>
        <mn>1</mn>
        <mo>+</mo>
        <mphantom>
          <mrow>
            <mn>2</mn>
            <mo>+</mo>
          </mrow>
        </mphantom>
        <mn>3</mn>
      </mrow>
    </mfrac>
  </mrow>
</math>