rec-diff2

W3C sample	WIRIS
	$\frac{d f(x)}{d x}$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <diff/>
    <bvar>
      <ci>x</ci>
    </bvar>
    <apply>
      <ci type="fn">f</ci>
      <ci>x</ci>
    </apply>
  </apply>
</math>

Author: MathML 2 Recommendation