use v5.30.0;
use strict;
#use re 'debug';
#use Regexp::Debugger;

my $str = '\'foooooooooobar and fubar\'';
say $str;

#
# Since + is 1 to unlimited, the unlimited exceeds 255, so unless you limit the max
# to something less than 255, the look behind will not compile.
#
my $re = qr/(?<=fo{1,254}?) \K obar/x;
say $re;
say "After exiting the look behind, Perl forgets whatever matched before \\K";
$str =~ $re;
say $& if $&;

exit(0);
__END__