In a previous article we spotlighted changes made to diffuse shading. The latest news is that Zmask rendering has been implemented and it now gives us the capability to create some complex composites.
Quote from Blender.org:
When you set up a scene for rendering, you typically want to separate a character in its own render-layer, for vector blur or color correction. Compositing it back in an environment then can be complicated... for example when the character stands in a grass field.
What you then need is a special render-layer, one that results in an image containing only the grass in front of the character. That is what the "Zmask" feature does for you.