use YAPE::Regex::Explain; my $r=YAPE::Regex::Explain->new(qr/^[\w @.]/); print $r->explain(); #### The regular expression: (?-imsx:^[\w @.]) matches as follows: NODE EXPLANATION ---------------------------------------------------------------------- (?-imsx: group, but do not capture (case-sensitive) (with ^ and $ matching normally) (with . not matching \n) (matching whitespace and # normally): ---------------------------------------------------------------------- ^ the beginning of the string ---------------------------------------------------------------------- [\w @.] any character of: word characters (a-z, A- Z, 0-9, _), ' ', '@', '.' ---------------------------------------------------------------------- ) end of grouping ----------------------------------------------------------------------