PHP PREG Regex: What does “\W” mean when using the UTF-8 modifier?

[mcmohanrtg]

I know that in normal php regex (ASCII mode) "\w" (word) means "letter, number, and _". But what does it mean when you are using multibyte regex with the "u" modifier?\[code\]preg_replace('/\W/u', '', $string);\[/code\]