utf8::upgrade($_);
/.../i

##</code><code>##

use feature 'unicode_strings'; 
/.../i

##</code><code>##

use 5.012;
/.../i

##</code><code>##

/.../iu

##</code><code>##

use re '/u';
/.../i

##</code><code>##

use utf8;  # Source file is encoded using UTF-8
print "é" =~ /É/i ?1:0,"\n";  # 1
print "É" =~ /é/i ?1:0,"\n";  # 1
print "é" =~ /\w/ ?1:0,"\n";  # 1
print "É" =~ /\w/ ?1:0,"\n";  # 1

##</code><code>##

use utf8;                             # UTF-8 code
use open ':std', ':encoding(UTF-8)';  # UTF-8 terminal
use 5.012;
$_ = "LES MISÉRABLES";
s/([^\x00-\x7F])/lc($1)/eg;  # LES MISéRABLES
say;