href3.test

<<< native
[ EIdentifier "x"
, ESymbol Rel "="
, EFraction
    NormalFrac
    (EGrouped
       [ ESymbol Bin "\8722"
       , EIdentifier "b"
       , ESymbol Bin "\177"
       , ESqrt
           (EGrouped
              [ ESuper (EIdentifier "b") (ENumber "2")
              , ESymbol Bin "\8722"
              , ENumber "4"
              , EIdentifier "a"
              , EIdentifier "c"
              ])
       ])
    (EGrouped [ ENumber "2" , EIdentifier "a" ])
]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mi>x</mi>
    <mo>=</mo>
    <mfrac>
      <mrow>
        <mo>−</mo>
        <mi>b</mi>
        <mo>±</mo>
        <msqrt>
          <mrow>
            <msup>
              <mi>b</mi>
              <mn>2</mn>
            </msup>
            <mo>−</mo>
            <mn>4</mn>
            <mi>a</mi>
            <mi>c</mi>
          </mrow>
        </msqrt>
      </mrow>
      <mrow>
        <mn>2</mn>
        <mi>a</mi>
      </mrow>
    </mfrac>
  </mrow>
</math>