say $-[1], ': ', $1 while 'olololo' =~ /
    (?=
        (
            (.)(?-2)\g-1 | (.).\g-1 
        )
    )
/gx;

say '*';

say 'match' if 'olololo' =~ /
    ^
    ( 
        (
            (.)(?-3)\g-1 | (.).\g-1 
        )
        (?{ 
            say $-[2], ': ', $2
        })
    )
    (?#*F)
/x;

##</code><code>##

0: olololo
1: lolol
2: ololo
3: lol
4: olo
*
4: olo
3: lol
2: ololo
2: olo
1: lolol
0: olololo
match

##</code><code>##

4: olo
3: lol
2: ololo
2: olo
1: lolol
0: olololo
1: lol
0: ololo
0: olo