Returns a list of a root element's descendants matching the given selector.
If the root element itself matches the selector, it is also included in the returned list.
Ignored elements
The following elements are ignored, even if they match the selector:
- Elements in a different layer than
root.
- Elements that are being destroyed with an animation.
- Elements that are being removed by a transition.
To include all elements matching the selector, use up.element.subtree().
