[css3-transforms] Skew is missing from 2D spec

I noticed skew(x, y) is missing from the 2d transforms spec: http://dev.w3.org/csswg/css3-2d-transforms/#effects but works fine in webkit, opera and FF (didn't test IE) I can't find old discussions of why it would be removed. It is in the http://www.w3.org/TR/css3-3d-transforms/#transform-functions functions, but appears to be a 2D feature and should therefore be included in the 2D tranforms definitions.

-Estelle