Paint server IRI in uDOM setTrait method of paint attribute

In the latest uDOM spec, why aren't paint server IRI values supported in
setTrait method of any paint attributes, e.g. fill? To my understanding if I
follow the spec, paint servers are currently unusable through uDOM.

I'd change the spec of fill attribute's setTrait method to:
setTrait [url(<Local IRI Reference>)| none | currentColor | inherit |
SVGRGBColor]

- CB