However, the change is not written in changelog etc., and it is understood only from the description of UTF-16 deleted from each documentation comment. In fact, swift-corelibs-foundation did not recognize that change was necessary, which caused SR-9454.
I think that some countermeasures are necessary:
[MUST] Behavior changes should be documented (eg within changelog).
[MAY] Some code change
Mark init(encodedOffset:) and encodedOffset as deprecated
Introduce new property exposing encode information(UTF-8 or UTF-16) to String