Comment 81 for bug 190848

Is it maybe a good idea to have is_set and not_set for compare attribute?

<match target="font">
  <test name="rgba" compare="not_set" />
  <edit name="rgba" mode="assign"><const>none</const></edit>
</match>

Even though it may be hard to determine which one (no-sub-pixel, sub-pixel-{bgr,rgb,vbgr,vrgb}) is better for. I guess this kind of config is never enabled by default and should simply leave it to the desktop preferences.