under big endian.
2. ":set octal" with nonprintable character causes nbwcurses move error.
3. moving (big)words by wW/eE/bB can't handle non-ascii characters.
4. toggle uppercase/lowercase by ~ can't handle non-ascii characters.
5. don't feed CHAR_T(=wchar_t) to is* function directly.
is* funcs with over UCHAR_MAX value may cause undefined behavior.
some ctype implementation(such as FreeBSD) return unexpected
result(same result as isw* func).
6. using non-ascii digit character with count/line number of ex/vi
command may causes unexpeced result.
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