Add prop getPosition()
For calculating position, FlipMove uses getBoundingClientRect. This method provides the top/left/right/bottom positions of the element relative to the viewport, and it's how FlipMove figures out where stuff needs to be moved to.
Unfortunately, it fails in certain situations (eg. inside a scaled container).
This prop allows you to specify a custom function to be used instead of getBoundingClientRect. It accepts the DOM node as an argument and should return an object with top/left/right/bottom and width/height properties.
It is unlikely to be needed by most users, but a good escape hatch to have when those situations come up :)
Huge props to @Guuz for his work implementing this feature.