texmath-0.12.5: test/writer/mml/mfrac3.test

<<< native
[ EFraction
    NormalFrac
    (EFraction NormalFrac (EIdentifier "a") (EIdentifier "b"))
    (EFraction NormalFrac (EIdentifier "c") (EIdentifier "d"))
]
>>> mml
<?xml version='1.0' ?>
<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mfrac>
    <mfrac>
      <mi>a</mi>
      <mi>b</mi>
    </mfrac>
    <mfrac>
      <mi>c</mi>
      <mi>d</mi>
    </mfrac>
  </mfrac>
</math>