[Paths] Catmull-Rom and other new path commands

I'm slightly concerned about adding new path commands, such as Catmull-Rom. I have nothing against the command itself, but I don't like that there is no nice fallback mechanism.

How am I supposed to author content that works in an engine that supports this feature, but also works in an engine that doesn't?

Maybe all new commands should be in a d2 attribute? Yuck. If you use the style approach, at least you could have multiple "d" properties.

Of course, as soon as you're providing fallback, it makes the argument for providing the new feature less compelling.

Dean

PS. And if we're going to break the syntax, why didn't we add an arc command that mortals can understand? :)