TransitionMotion has no easing into new location for adjacent elements in the set that are not mounting/unmounting

I am animating typing **numbers only** in an input field, and having commas animate in as well.

The TransitionMotion API has been mostly fantastic, but I noticed significant difficulty getting the **surrounding** elements of the nodes that were entering and leaving the DOM to animate smoothly into their new positions. An exploration of `react-flip-move` proved significantly easier.

I prefer `react-motion` to `react-flip-move` because it can handle rapid animations, perfect for typing. I think the jarring, instant movement to a new location of all non-animating nodes in the mapped set defeats the benefit of enter/leave animations for single nodes in a set.

Thanks 🙂

Start by reproducing the reported TransitionMotion behavior with a numeric-only input whose comma elements enter and leave. Compare the movement of adjacent, non-mounting elements with the smoother behavior observed in react-flip-move. Done means surrounding elements animate into their new positions instead of moving there instantly during enter/leave transitions.

Written by the indexing model from the issue text.