Operational Transform
- http://operational-transformation.github.io/
- https://jzhao.xyz/thoughts/Operational-Transform
- http://objcer.com/2018/03/05/SharePen-Operational-Transformation/
- https://fitzgeraldnick.com/2011/04/05/operational-transformation-operations.html
- https://github.com/ottypes/text
- https://digitalfreepen.com/2018/01/04/operational-transform-hard.html