[css-transforms-1] 2D rotations are not actually defined in a clear way

[bzbarsky]

https://drafts.csswg.org/css-transforms-1/#RotateDefined says:

A 2D rotation with the parameter alpha is equivalent to a 3D rotation with vector [0,0,1] and parameter alpha.

Presumably this is meaning to reference the definition at https://drafts.csswg.org/css-transforms-2/#Rotate3dDefined but that's not at all clear from the text. This definition should have a link to css-transforms-2.

[dirkschulze]

I think we simply removed the 3D part and missed to update the 2D transform descriptions.

[dirkschulze]

@bzbarsky I restored the original text and images. CSS Transforms 1 is not supposed to reference level 2. (Since the latter builds up on top of the former.)

[bzbarsky]

Hmm. I guess that works, through if x = y = 0 and z = 1, the matrix can be written much more simply...