Based on idea from Raimund Steger.

For example, one can do something like this:

<match target="font">
  <test name="scalable" compare="eq">
    <bool>false</bool>
  </test>
  <edit name="pixelsizefixupfactor" mode="assign">
    <divide>
      <name target="pattern">pixelsize</name>
      <name target="font"   >pixelsize</name>
    </divide>
  </edit>
  <edit name="matrix" mode="assign">
    <times>
      <name>matrix</name>
      <matrix>
        <name>pixelsizefixupfactor</name> <double>0</double>
        <double>0</double> <name>pixelsizefixupfactor</name>
       </matrix>
    </times>
  </edit>
</match>

Part of work to make bitmap font scaling possible.  See thread
discussion:

http://lists.freedesktop.org/archives/fontconfig/2012-December/004498.html