Regexp
I just had to troubleshoot an issue with regular expressions used in validators of the Zend Framework.
They worked locally but not on the servers in the hosting center.
I tracked it down to missing UTF-8 support in the PCRE library on those servers.
They were on Cent OS. Recompiling the package with that support switched on fixed it.
Further research turned up this thread that lists some platforms known to
have this problem: http://framework.zend.com/issues/browse/ZF-1641
