[Fontconfig] Do you know how to use binary operators like or, and in fonts.conf?

[Zhe Su]

Hi,
  I can't find any example for those kind of binary operators. What I
want is to match one of two families and do some modification for that
pattern.
  I tried the following code, but didn't take effect:

  <match target="pattern">
    <or>
      <test name="family"><string>Font A</string></test>
      <test name="family"><string>Font B</string></test>
    </or>
    <edit name="family" mode="prepend">
      <string>Font C</string>
    </edit>
  </match>

  Do you know what's wrong with this piece of code?

Regards
James Su