I\'ve a PHP library that uses a number of regular expressions featuring the \\P expressions for multibyte strings, e.g.
((((?:\\P{M}\\p{M}*)+?)|
While comments suggest checking for PREG_BAD_UTF8_ERROR the PHP source http://lxr.php.net/xref/PHP_5_6/ext/pcre/php_pcre.c#141 suggests this constant is always available if PCRE is. Indeed it seems --enable-unicode-properties is a PCRE lib switch and is simply not exposed by PHP. The only thing I can imagine is running a simple regexp once with warning supressed...