<<< 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"
       ])
]
>>> omml
<?xml version='1.0' ?>
<m:oMathPara>
  <m:oMathParaPr>
    <m:jc m:val="center" />
  </m:oMathParaPr>
  <m:oMath>
    <m:r>
      <m:t>A</m:t>
    </m:r>
    <m:phant>
      <m:phantPr>
        <m:show m:val="0" />
      </m:phantPr>
      <m:e>
        <m:r>
          <m:t>A</m:t>
        </m:r>
      </m:e>
    </m:phant>
    <m:r>
      <m:t>A</m:t>
    </m:r>
    <m:r>
      <m:rPr>
        <m:sty m:val="p" />
      </m:rPr>
      <m:t>+</m:t>
    </m:r>
    <m:f>
      <m:fPr>
        <m:type m:val="bar" />
      </m:fPr>
      <m:num>
        <m:r>
          <m:t>1</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>+</m:t>
        </m:r>
        <m:r>
          <m:t>2</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>+</m:t>
        </m:r>
        <m:r>
          <m:t>3</m:t>
        </m:r>
      </m:num>
      <m:den>
        <m:r>
          <m:t>1</m:t>
        </m:r>
        <m:r>
          <m:rPr>
            <m:sty m:val="p" />
          </m:rPr>
          <m:t>+</m:t>
        </m:r>
        <m:phant>
          <m:phantPr>
            <m:show m:val="0" />
          </m:phantPr>
          <m:e>
            <m:r>
              <m:t>2</m:t>
            </m:r>
            <m:r>
              <m:rPr>
                <m:sty m:val="p" />
              </m:rPr>
              <m:t>+</m:t>
            </m:r>
          </m:e>
        </m:phant>
        <m:r>
          <m:t>3</m:t>
        </m:r>
      </m:den>
    </m:f>
  </m:oMath>
</m:oMathPara>