[css3-background][css3-compositing] box-shadow blending

All,

the css compositing and blending spec defines how a box shadow can blend
with its background [1].
It seems that it would be easier if the blend mode became a part of the
shadow syntax [2]. That way there would be no need for another css property.
What do people think about this?

Another interesting feature would be if box shadows could be marked as
'knockout' When in this mode, shadows would not interact with each other so
if a shadow has opacity, you will not see the sibling shadows.

Rik

1:
https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#box-shadow-blend-mode
2: http://dev.w3.org/csswg/css4-background/#ltshadowgt