The Focusable plugin finds all draggable containers and elements on initialization
and decorates them with tabindex attributes.
The plugin will not override existing tabindex attributes on elements. This will
make draggable elements and containers focusable.
new Focusable(draggable: Draggable): Focusable
To create an focusable plugin instance.
focusable.getElements(): HTMLElement[]
Returns container and draggable elements.
No options