c:\@Work\Perl\monks>perl -wMstrict -le
"use YAPE::Regex::Explain;
 ;;
 my $rx = qr{www.([A-Z a-z 0-9]+.{3}).}x;
 ;;
 print YAPE::Regex::Explain->new($rx)->explain;
"
The regular expression:

(?x-ims:www.([A-Z a-z 0-9]+.{3}).)

matches as follows:

NODE                     EXPLANATION
----------------------------------------------------------------------
(?x-ims:                 group, but do not capture (disregarding
                         whitespace and comments) (case-sensitive)
                         (with ^ and $ matching normally) (with . not
                         matching \n):
----------------------------------------------------------------------
  www                      'www'
----------------------------------------------------------------------
  .                        any character except \n
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    [A-Z a-z 0-9]+           any character of: 'A' to 'Z', ' ', 'a'
                             to 'z', ' ', '0' to '9' (1 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
    .{3}                     any character except \n (3 times)
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  .                        any character except \n
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------