>perl -e 'use 5.018; my $x=qr/a[bc]d/; say("|$_| matches |$x|: ",$_=~/$x/ ? "yes" : "no") for ( "abd","acd","abcd","a[bc]d" )'
|abd| matches |(?^u:a[bc]d)|: yes
|acd| matches |(?^u:a[bc]d)|: yes
|abcd| matches |(?^u:a[bc]d)|: no
|a[bc]d| matches |(?^u:a[bc]d)|: no
>