rec-abs3

W3C sample	WIRIS
[N/A]	$abs x$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <csymbol cd="arith1">abs</csymbol>
    <ci>x</ci>
  </apply>
</math>

Author: MathML 2 Recommendation