$ perl -CS -Mstrict -wE 'say "\x{ab}oo\x{bb}"'
«oo»
$ perl -CS -Mstrict -wE 'say utf8::is_utf8 "\x{ab}oo\x{bb}"'

$ # let's convince ourselves that lc() works properly:
$ perl -CS -Mstrict -wE 'say "\x{C6}"'
Æ
$ perl -CS -Mstrict -wE 'say lc "\x{C6}"'
æ
$ perl -CS -Mstrict -wE 'say utf8::is_utf8 "\x{C6}"'

$