What does zend.multibyte directive exactly affect?

I am using UTF8 encoding without BOM for all my php scripts for years, and they work fine. Today i discovered that thereis core directive named zend.multibyte, and it is zero (disabled) by default.

So, if it does not affect scripts parsing.. what exactly does it affect?

Answer

Zend Multibyte is needed for ASCII-incompatible encodings, like some Asian encodings from pre-unicode/pre-utf-8 times and is mostly used in Japan. when enabled the parser will check mbstring.script_encoding and use that encoding while parsing. As internally some conversions happen this should be avoided, but for some users is the only way they can use PHP.