`merror` (unary)

Merror

MathML

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mstyle displaystyle="true">
    <merror>
      <mi>x</mi>
    </merror>
  </mstyle>
</math>

Note	In other conversions, the value of the class will not be processed at all.