perldoc -f open

##</code><code>##

The regular expression:
 
(?-imsx:\b[Ii]t\b(.*)[.,?]$)
 
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):
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
  [Ii]                     any character of: 'I', 'i'
----------------------------------------------------------------------
  t                        't'
----------------------------------------------------------------------
  \b                       the boundary between a word char (\w) and
                           something that is not a word char
----------------------------------------------------------------------
  (                        group and capture to \1:
----------------------------------------------------------------------
    .*                       any character except \n (0 or more times
                             (matching the most amount possible))
----------------------------------------------------------------------
  )                        end of \1
----------------------------------------------------------------------
  [.,?]                    any character of: '.', ',', '?'
----------------------------------------------------------------------
  $                        before an optional \n, and the end of the
                           string
----------------------------------------------------------------------
)                        end of grouping
----------------------------------------------------------------------

##</code><code>##

#!/usr/bin/env perl
use warnings;
use strict;
use YAPE::Regex::Explain;

my $re = '\b[Ii]t\b(.*)[.,?]$';
my $parser = YAPE::Regex::Explain->new($re);
print $parser->explain;