I think I'll be a little bit off topic but I don't know where to ask (my question about svg on inkscapeforum are left unanswered)

Can someone point me to reference papers (or friendly forum) about coefficients in FeColorMatrix, Fecomposite ?
Something that could answer the following questions :

What are safe values ? For exemple inkscape UI allows x10 for k1,k2,k3,k4 in FeComposite, can I push to 255 ? 256 ? 1000000 ?
I don't see anything in SVG spec about max values for those coeffs.

What about neg values ? When does clipping occur ? Particularly for k4.

What is the effect of a <100% opacity source or dest ? (On clipping for exemple)

I try to port svg2 PorterDuff operations in svg 1 and I often get strange results (to me) with inkscape. Is there some known bugs in rendering fecomposite with neg values in inkscape ?



Bonus question : why is inkscape so slow at rendering filters ? ;)