[jacobolus]

The CSS 2D transforms are frustratingly crippled in my opinion. Instead of allowing the specification of a full 3x3 matrix for doing homogeneous coordinate transformations (and thus general perspective transforms), only a 2x3 matrix can be specified. I’m really glad they actually give access to the whole 4x4 matrix in the 3D version.

[ionfish]

Yes, it's a big improvement. The WebKitCSSMatrix implementation is actually compatible with both specifications: it provides getters and setters for elements a-f as well as m11-m44, and serialises to "matrix(a, b, c, d, e, f)" if the matrix is affine.