#!/usr/bin/perl -w
use strict;

my $regexp = qr/^x/i;                             # a regexp

# stringify it
my $hash   = { $regexp => 1 };                    # keys are stringified
my $string = (keys %$hash)[0];                    # a string

print "$string (ref: ", ref $string,")\n";        # and I prove it!
                                                  # the string is: '(?i-xsm:^x)'

# regex-ify it
if( $string=~m{^\(\?([xism]*)-([xism]*):(.*)\)$}) # match the interesting bits    
  { my $nregexp= qr/(?$1:$3)/;                    # rebuild it
    print "$nregexp (ref: ", ref $nregexp,")\n";  # a regexp again! 
                                                  # it stringifies as '(?-xism:(?i:^x))'
  }