SVG Paths DOM interface is underspecified

[longsonr]

• SVG Paths DOM interfaces

• normalize in SVGPathDataSettings does not go into any details about how it works. An algorithm detailing how normalisation works, particularly for elliptical arcs might well improve interoperability.
• setPathData what happens if the path data cannot be completely parsed. Do we (like for markup) parse till we get an error? Do we silently ignore subsequent data?
• SVGPathSegment is [NoInterfaceObject] so how is one supposed to create additional path segments e.g. to make a path longer in javascript?