For natural language processing (so that, for example, apostrophes are included in words), use instead \b{wb}</p>

"don't" =~ / .+? \b{wb} /x;  # matches the whole string
##</code><code>##

use warnings;
use strict;
use feature qw{ say };

if ("don't" =~ / (.+?) (\b{wb}) /x) {  # matches the whole string
    print "It matches\n";
    say $1;
    say $2;
}
else {
    print "It doesn't match\n";
}

if ("don't" =~ / (.+?) /x) {  # It no longer matches the whole string
    print "It matches\n";
    say $1;
}
else {
    print "It doesn't match\n";
}

Output:
It matches
don't

It matches
d