badAttribs2.mml

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

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <msup foo="blue">
    <mn>2</mn> 
    <mn>5</mn> 
  </msup> 
  <mo bar="2ex">+</mo> 
  <mi>x</mi> 
</math>