rec-partialdiff3

W3C sample	WIRIS
	$\frac{\partial^{k}f(x, y)}{\partial x^m\partial y^n}$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <apply>
    <partialdiff/>
    <bvar>
      <ci>x</ci>
      <degree>
        <ci>m</ci>
      </degree>
    </bvar>
    <bvar>
      <ci>y</ci>
      <degree>
        <ci>n</ci>
      </degree>
    </bvar>
    <degree>
      <ci>k</ci>
    </degree>
    <apply>
      <ci type="fn">f</ci>
      <ci>x</ci>
      <ci>y</ci>
    </apply>
  </apply>
</math>

Author: MathML 2 Recommendation