Elements are assigned the .up-destroying class before they are destroyed
or while they are being removed by a transition.
If the removal is animated,
the class is assigned before the animation starts.
Destroying elements are ignored
Destroyed element remain attached to the DOM while they are playing out their exit animation.
To prevent accidental selection of destroying elements, they are ignored by
Unpoly features like [up-target] or up.fragment.get().
Only the low-level DOM helpers in up.element will not ignore elements that are being destroyed.
Accessibility
While an element's destruction is animating, the element is also assigned an
[inert] attribute.
This prevents interaction with the element and hides it from assistive technologies.
