[css-compositing] group isolation and filters

All,

We have an offline discussion on the question if filters should cause
groups to be isolated?
The current Filters spec does not require this [1]

Since this concept is hard to grasp I attached an example how this changes
rendering.

The example at the top is a group that contains a blue and a green
rectangle that is on top of a red rectangle.
In the second line, the green rectangle has a blend mode attached to it.
In the bottom line, there are 2 possible rendering for when the group has a
filter effect applied to it.

My question is: what would you expect the result to be? A or B

Rik

1:
https://dvcs.w3.org/hg/FXTF/raw-file/tip/filters/index.html#AccessBackgroundImage