More about regular expressions
Regular expressions can be as simple or complex as your environment requires, but use them with care. Poorly constructed regular expressions can result in excessive filtering overhead.
As with keywords, if non-ASCII characters appear in a regular expression, the expression is matched against only the path and query (CGI) strings in the URL. No matching is done against the domain.
If only ASCII characters appear in the regular expression, the match is performed against the entire URL.
Most Perl regular expression syntax is supported.
For further help with regular expressions, see: