Scene graph nodes have three focus-related properties: 1. focused 2. focus-within 3. focus-visible
What might be a bit surprising is that multiple nodes can be focused at the same time, but only one of those focused nodes can be the scene's focus owner. The `Scene.focusOwner` property indicates which of the focused nodes is the current focus owner. Even more surprisingly, a node can be _unfocused_ and be the focus owner at the same time (this can happen when the window is deactivated). >From the perspective of `Node`, there's currently no API to easily determine whether it is the focus owner, and there's no CSS pseudo-class that matches a node that is the focus owner. We could add two more properties to the `Node` class to support this use case: 4. focus-owner 5. focus-owner-within Note that `focus-visible` only matches nodes that are also focus owners, so there's no need to have a `focus-owner-visible` property. The two additional properties would suffice to match any possible focus state, but it might also be not useful enough to warrant the additional API surface. What do you think?
