Do you want to know how the CSS WG works? Fantasai has written about:csswg, An Inside View of the CSS Working Group at W3C.
animation-directionreverses an animation, the timing function goes in reverse
z-indexis *not* optional on page-margin boxes.
image()for fallbacks, and where to register new subtypes.
displayshorthand, so that it is not accidentally reset by style rules setting the box type