@mikebabcock @krans What does that mean precisely though? (IOW what do you mean by "encoding system of UCS"?)
UTF-8 was originally conceived without a lot of rigor as an encoding of 31-bit numbers with non-unique encodings, but that was quickly realized to be a mistake and fixed. The other UTFs, and the unified definition of a UTF (which also includes GB18030!), were developed more rigorously, and involve the concept of USVs.