[this restriction is needed because of BIG5, BIG5-HKSCS, GBK, GB18030,
Shift_JIS, JOHAB], and
3. does not consist entirely of decimal digits, or has at least length 4
- [this restricion is needed because of GB18030].
+ [this restriction is needed because of GB18030].
This function is also safe to be called, even in a multibyte locale, if
HAYSTACK and NEEDLE are known to both consist solely of printable ASCII
characters excluding '\\' and '~'. */