Compositing describes how shapes of different elements are combined into a single image.

There are various possible approaches for compositing.

Previous versions of SVG and CSS used Simple Alpha Compositing

In this model, each element is rendered into its own buffer and is then merged with its backdrop using the Porter Duff source-over operator

This specification will define a new compositing model that expands upon the Simple Alpha Compositing model by offering:

--additional Porter Duff compositing operators

--advanced blending modes which allow control of how colors mix in the areas where shapes overlap

--compositing groups