[css-shapes] Purpose of fill-rule not specified

Reading the spec I couldn't see what the consequence of specifying a
fill-rule would be. For example, what is the expected behaviour of a
left-float with a declaration of

shape-outside: polygon(0px 150px,100px 150px,100px 50px,50px 50px,50px
100px,100px 100px,100px 0px,0px 0px);

with fill-rules of nonzero or evenodd? (See SVG of this here:
http://codepen.io/karaken12/pen/gpdwKO?editors=100)

I would expect Case 3 to behave the same as Case 1, but I don't think this
is specified. If I've misunderstood and this is already defined then
perhaps it could be called out as an example?

Cheers,
Tom