I don't really understand how it can use UCS-2. I don't think UCS-2 can represent emoji.
What's cool is that UCS-2 and UTF-16 behave the same way in this regard, so you can see how this works in JavaScript as well. There's a great HN post about the length of an emoji being 2 in JS [1] from 2017.
Practically speaking, I had fun learning this while writing an Angular app to read SMS backups [2]. It's frustrating and cool at the same time.
[1] https://news.ycombinator.com/item?id=13830177
[2] https://github.com/devadvance/sms-backup-reader-2/blob/maste...
>UCS-2 differs from UTF-16 by being a constant length encoding[4] and only capable of encoding characters of BMP.
https://en.wikipedia.org/wiki/UTF-16
There does seem to be some disagreement on this topic though. I wonder if it could be described as WTF-16.
UTF-16 can represent all Unicode code points, through surrogate pairs when needed.
Systems that originally were designed for UCS-2 have often been upgraded to UTF-16. E.g. Windows, JS. But it is then not UCS-2 anymore. In some case the documentation and/or function names, etc., might talk incorrectly about being UCS-2 (while they really are UTF-16 now) for historical reasons, adding to the confusion.