pcre is locale aware so there are some exceptions. What locale are you using?

Also we use PCRE which is not the Microsoft regexp syntax, I suggest you read the PHP manual instead.

What's locale?

[\W] is identical to [^A-Za-z0-9_] is not only Microsoft idea.

\W means matching any nonword character is the same of [^\w] which is the same of [^A-Za-z0-9_]
[http://en.wikipedia.org/wiki/Regular_expression#POSIX_character_classes]

Also many other website that talks about reg exp say the same thing of Microsoft and wikipedia, you can search in Google.

Sorry, but this is a bug!


BTW: php manual is completly useless regarding regular expression sintax, it does not help in any way, that's why I added the Microsoft documentation link.

http://uk.php.net/manual/en/regexp.reference.backslash.php clearly explains it:

\w
    any "word" character
\W
    any "non-word" character

Each pair of escape sequences partitions the complete set of characters into two disjoint sets. Any given character matches one, and only one, of each pair.

A "word" character is any letter or digit or the underscore character, that is, any character which can be part of a Perl "word". The definition of letters and digits is controlled by PCRE's character tables, and may vary if locale-specific matching is taking place. For example, in the "fr" (French) locale, some character codes greater than 128 are used for accented letters, and these are matched by \w. 

To me this only means that also the PHP documentation is wrong.

1st) there is a paradox:
if [\w] (I tested same issue of \W) does the matching depending on local setting then also [A-Za-z_] (which is the same of [\w] should behave in the same way and match also accented character like ????? depending on local setting, since it does not happen this last one would be the bug.

2nd) I wonder how to acknowledge all websites on the internet (including Wikipedia) that PHP reg expression sintax is different from the common sense standard of the rest of the world!



PS
I adore PHP, just trying to help. Bye!)

We have Perl Compatible Regular Expressions *NOT* POSIX regular expressions.

Ok, I read documentation at http://perldoc.perl.org/perlre.html#Regular-Expressions

But this anyway is an issue (almost a bug), on the web environment.
Because my regexp would change bahaviour depending upon the locale settings of the server.
How do I make sure all servers running my web apllication have the same locale settings.

Thanks anyway for the explanation.
I'm gonna t add a comment on preg_replace PHP documentation.
PHP forever!)