>> We might keep the old public API for compatibility, but it should be
>> clearly marked as broken for non-BMP scalar values.

> That has always been the case. UCS2 doesn't support surrogates.

> However, we have been slowly moving into the direction of making
> the UCS2 storage appear like UTF-16 to the Python programmer.

UCS2 died long ago, is there any reason why we keep using an UCS2 that
"appears" like UTF-16 instead of real UTF-16?

> This process is not yet complete and will likely never complete
> since it must still be possible to create things line lone
> surrogates for processing purposes, so care has to be taken
> when using non-BMP code points on narrow builds.

I don't exactly know all the details of the current implementation, but
-- from what I understand reading this (correct me if I'm wrong) -- it
seems that the implementation is half-UCS2 to allow things like the
processing of lone surrogates and half-UTF16 (or UTF-16-compatible) to
work with surrogate pairs and hence with chars outside the BMP.

What are the use cases for processing the lone surrogates? Wouldn't be
better to use UTF-16 and disallow them (since they are illegal) and
possibly provide some other way to deal with them (if it's really needed)?