[fxtf-drafts] [filter-effects] Clarify mapping of Cs and Cb to in and in2 in feBlend

BigBadaboom has just created a new issue for https://github.com/w3c/fxtf-drafts:

== [filter-effects] Clarify mapping of Cs and Cb to in and in2 in feBlend ==
https://www.w3.org/TR/filter-effects/#element-attrdef-feblend-mode

The definition for the mode attribute of <feBlend> states:

> One of the blend modes defined by “Compositing and Blending Level 1” [COMPOSITING-1]

However that specification defines the blend functions in terms of source (Cs) and backdrop (Cb) parameters.  We should specify how `in` and `in2` map to those two values.

>From testing (Chrome and FF) it appears that Cs maps to `in`, and Cb maps to `in2`.



Please view or discuss this issue at https://github.com/w3c/fxtf-drafts/issues/165 using your GitHub account