PHP: what is --enable-zend-multibyte configure option for?

It is to be able to detect if PHP scripts are Unicode/Multibyte encoded or not (UTF-8 always works and does not need this setting).

I've found this information in this article http://devzone.zend.com/article/2693 (archived copy, the article itself is outdated).

It is a prerequisite for declare(encoding) handling.

Apart from that, I have filed a bug about the lack of documentation for this: http://bugs.php.net/bug.php?id=52348