[API Review]: Node validation

[Richard Bair]

>> This might work for CSS, but won't for layout. The second example won't work because you'd just do layout of the node itself. It might get a different size from it's parent during the next layout pass (and the parent from it's parent, etc...). So the layout will look different after the next pulse. This is why we need more than layout() call and it's not just about adding the CSS.
> 
> If I understand properly this would be the correct behavior.  If I ask a subtree of nodes to layout after setting the size of the subtree root, then go farther up the tree to an ancestor, ensure the ancestor has a size and layout again, the original subtree might be layed out differently and I would expect that.  If I need to take a snapshot of a child and it has to be in context of the entire tree, I do CC in the root, force layout in the root and then take a snapshot of the child.

That was what I was thinking as well, I don't understand why we have to do more than provide a way to apply CSS in order to satisfy all the use cases? Note that the old implementation (with lists of dirty roots on the Scene, or is this still the way we do it?) might be problematic here, I don't know, but from an API point of view, it seems like this is exactly what you want.

Richard