mfracAkeyword9

W3C sample	WIRIS
	$\genfrac{}{}{.05ex}{}{1}{y+3}\genfrac{}{}{}{}{1}{y+3}\genfrac{}{}{.2ex}{}{1}{y+3}$

<math xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mfrac linethickness="thin">
      <mn>1</mn>
      <mrow>
        <mi>y</mi>
        <mo>+</mo>
        <mn>3</mn>
      </mrow>
    </mfrac>
    <mfrac linethickness="medium">
      <mn>1</mn>
      <mrow>
        <mi>y</mi>
        <mo>+</mo>
        <mn>3</mn>
      </mrow>
    </mfrac>
    <mfrac linethickness="thick">
      <mn>1</mn>
      <mrow>
        <mi>y</mi>
        <mo>+</mo>
        <mn>3</mn>
      </mrow>
    </mfrac>
  </mrow>
</math>

Author: Robert Miner and Jeff Schaefer, Geometry Technologies