[cairo] Layered stroke / fill

[Cosmin Apreutesei]

> Just stroke and fill each rectangle individually. Adding all rectangles
> to the path then calling stroke/fill operates on the union of that path.

Wow, I didn't know that. Is this documented somewhere? I thought that
a path with different closed subpaths would operate identically with
multiple paths.

Does that mean that cairo has code for path union inside? If so, could
this be exposed?