<<< mml
<?xml version="1.0" encoding="UTF-8"?>

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mn>2</mn> 
  <mo>+</mo> 
  <mphantom>
    <foo>14</foo> 
  </mphantom> 
</math>
>>> native
Unexpected element foo line 7