String::Multibyte::UHC is used for manipulation of strings
in UHC (Unified Hangul Code).
Byte range of single-byte characters:
Leading byte range of double-byte characters:
Trailing byte range of double-byte characters:
0x41..0x5A, 0x61..0x7A, and 0x81..0xFE.
Unassigned code points out of EUC-KR are disabled.
Character order (invalid code points are excluded):